Starting level peep. Ventilation with positive end expiratory pressure (PEEP)

Essentially, the differences between all these modes are explained only by different software, and the ideal program has not yet been created. It is likely that the progress of VTV will be associated with the improvement of programs and mathematical analysis of information, and not with fan designs, which are already quite perfect.

The dynamics of changes in pressure and gas flow in the patient's respiratory tract during the respiratory cycle during forced TCPL ventilation is illustrated in Fig. 4, which schematically shows parallel graphs of pressure and flow over time. Actual pressure and flow curves may differ from those shown. The reasons and nature of the configuration change are discussed below.

PARAMETERS TCPL VENTILATION.

The main parameters for TCPL ventilation are those that are set by the doctor on the device: flow, peak inspiratory pressure, inspiratory time, expiratory time (or inspiratory time and respiratory rate), positive

Abbreviation" href="/text/category/abbreviatura/" rel="bookmark">abbreviations and names (as they are indicated on the control panels of ventilators).

In addition to the main parameters, derivative parameters are of great importance, that is, those that arise from a combination of basic parameters and the state of the patient’s pulmonary mechanics. Derived parameters include: mean airway pressure (one of the main determinants of oxygenation) and tidal volume - one of the main parameters of ventilation.

Flow

This parameter refers to the constant inspiratory flow in the patient's breathing circuit (not to be confused with the flow of the inspiratory tract). The flow rate must be sufficient to achieve the set peak inspiratory pressure within the set inspiratory time when the APL valve is closed. The flow rate depends on the patient's body weight, the capacity of the breathing circuit used, and the magnitude of the peak pressure. A flow of 6 liters/min is sufficient to ventilate an average full-term newborn with physiological parameters using a standard neonatal breathing circuit. For premature babies, a flow of 3–5 liters/min may be sufficient. When using different models of “Stephan” devices that have a breathing circuit of smaller capacity than a standard disposable one, lower flow values ​​can be used. If it is necessary to use high peak pressures with a high frequency of respiratory cycles, it is necessary to increase the flow to 8 - 10 l/min, since the pressure must rise within a short time of inspiration. When ventilating children weighing 12 kg. (with larger breathing circuit capacity) flows of 25 L/min or higher may be required.

The shape of the pressure curve in the respiratory tract depends on the magnitude of the flow. An increase in flow causes a faster rise in pressure in the blast furnace. Too much flow instantly increases the pressure in the air chamber (aerodynamic shock) and can cause anxiety in the child and provoke a “struggle” with the fan. The dependence of the shape of the pressure curve on the flow rate is illustrated in Fig. 5. But the shape of the pressure curve depends not only on the flow rate, but also on compliance (WITH) the patient's respiratory system. At low WITH pressure equalization in the patient circuit and alveoli will occur faster, and the shape of the pressure curve will approach square.

The choice of flow rate also depends on the size of the endotracheal tube, in which turbulence may occur, reducing the effectiveness of spontaneous breaths and increasing the work of breathing. In IT Ø 2.5 mm, turbulence appears at a flow of 5 l/min, in IT Ø 3 mm at a flow of 10 l/min.

The shape of the flow curve in the AP depends on the flow rate in the patient circuit. At low flows, gas compression in the breathing circuit plays a role (primarily in the humidifier chamber), so the inspiratory flow first increases and then falls as the lungs fill. At high flow, gas compression occurs quickly, so the inspiratory flow immediately arrives at its maximum value. (Fig.6)

In conditions with high Raw and regional unevenness of ventilation, it is preferable to choose such flow values ​​and inhalation time as to ensure a pressure curve shape close to triangular. This will lead to an improvement in the distribution of tidal volume, that is, it will avoid the development of volume trauma in areas with normal values Raw.

If the patient's spontaneous breaths cause the circuit pressure to decrease > 1 cmH2O, the flow is insufficient and should be increased.

In single-flow devices (inspiratory and expiratory), high flow rates in a small internal diameter breathing circuit can create resistance to expiration, which increases the PEEP value (above the set value) and can increase the patient's work of breathing, causing active expiration.

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Fig 6. Dynamics of flow in the DP at different flow rates in the breathing circuit

A) The inspiratory flow increases, but does not have time to fill the lungs in time

C) Inspiratory flow fills the lungs, decreases and stops earlier

the time of exhalation has arrived.

Peak inspiratory pressure – PIP ( peak inspiratory pressure).

PIP is the main parameter that determines the tidal volume (Vt), although the latter also depends on the level of PEEP. That is, Vt depends on ΔP=PIP-PEEP (drive pressure), but the PEEP level fluctuates in a much smaller range. But Vt will also depend on pulmonary mechanics. When increasing Raw(SAM, BPD, bronchiolitis, endotracheal tube obstruction) and short inspiratory time, Vt will decrease. When decreasing WITH(RDS, pulmonary edema) Vt will also decrease. Increase WITH(surfactant administration, dehydration) will increase Vt. In patients with high compliance of the respiratory system (premature infants with healthy lungs who are undergoing mechanical ventilation for apnea or surgical treatment), the PIP value to ensure adequate ventilation can be 10 - 12 cm H2O. For full-term newborns with normal lungs, PIP = 13 - 15 cm H2O is usually sufficient. However, in patients with “hard” lungs, PIP > 25 cm H2O may be required to achieve the minimum Vt, i.e. 5 ml/kg body weight.

Most complications of mechanical ventilation are associated with incorrect selection of the PIP value. High PIP values ​​(25 – 30 cmH2O) are associated with baro/volume injury, decreased cardiac output, increased intracranial pressure, hyperventilation and its consequences. Insufficient PIP (individual for each patient) is associated with atelectrauma and hypoventilation.

The easiest way to select an adequate PIP value is to achieve “normal” chest excursions. However, such selection is subjective and should be supported by auscultatory data and (if possible) respiratory monitoring, that is, Vt measurement, determination of curve and loop shapes, as well as blood gas analysis data.

To maintain adequate ventilation and oxygenation, PIP values ​​should be kept as low as possible, as this reduces tissue stress and the risk of developing ventilator-induced lung injury (VILI).

Positive end expiratory pressure – PEEP

( positive end- expiratory pressure).

Each intubated patient should be provided with a PEEP level of at least 3 cm H2O, which simulates the effect of glottis closure during normal exhalation. This effect prevents the development of ECDP and maintains FRC. FRC = PEEP × C during mechanical ventilation. Ventilation with a zero level of PEEP - ZEEP (zero end-expiratory pressure) is a mode that damages the lungs.

PEER prevents the collapse of the alveoli and promotes the opening of non-functioning bronchioles and alveoli in premature infants. PEEP promotes the movement of alveolar fluid into the interstitial space (baby lung effect), thus maintaining the activity of surfactant (including exogenous). With reduced compliance of the lungs, an increase in the level of PEEP facilitates the opening of the alveoli (recruitment) and reduces the work of breathing during spontaneous inspiration, and the compliance of the lung tissue increases, but not always. An example of improving lung compliance with increasing PEEP to the level of CPP (collapse pressure point) is illustrated in Fig. 7.

Fig 7. Increased compliance of the respiratory system with increasing PEEP

to the level of SRR.

If a decrease in the compliance of the respiratory system is associated with thoracoabdominal factors (pneumothorax, high position of the diaphragm, etc.), then an increase in PEEP will only worsen hemodynamics, but will not improve gas exchange.

During spontaneous breathing, PEEP reduces the retraction of the compliant areas of the chest, especially in premature infants.

With TCPL ventilation, an increase in PEEP always reduces ΔP, which determines Vt. A decrease in tidal volume can lead to the development of hypercapnia, which will require an increase in PIP or respiratory rate.

PEEP is the ventilation parameter that most influences MAP (mean airway pressure) and, accordingly, oxygen diffusion and oxygenation.

Selecting an adequate PEEP value for each individual patient is not an easy task. The nature of lung damage (radiographic data, configuration of the P/V loop, the presence of extrapulmonary shunting), and changes in oxygenation in response to changes in PEEP should be taken into account. When ventilating patients with intact lungs, PEEP = 3 cm H2O should be used, which corresponds to the physiological norm. In the acute phase of pulmonary diseases, the PEEP level should not be< 5см Н2О, исключением является персистирующая легочная гипертензия, при которой рекомендуется ограничивать РЕЕР до 2см Н2О. Считается, что величины РЕЕР < 6см Н2О не оказывают отрицательного воздействия на легочную механику, гемодинамику и мозговой кровоток. Однако, Keszler M. 2009; считает, что при очень низкой растяжимости легких вполне уместны уровни РЕЕР в 8см Н2О и выше, которые способны восстановить V/Q и оксигенацию. При баротравме, особенно интерстициальной эмфиземе, возможно снижение уровня РЕЕР до нуля, если нет возможности перевести пациента с CMV на HFO. Но при любых обстоятельствах оптимальными значениями РЕЕР являются наименьшие, при которых достигается наилучший газообмен с применением относительно безопасных концентраций кислорода.

High PEEP values ​​have an adverse effect on hemodynamics and cerebral blood flow. Decreased venous return reduces cardiac output and increases hydrostatic pressure in the pulmonary capillaries (hemodynamic alteration), which may require the use of inotropic support. Lymphatic drainage worsens not only in the lungs, but also in the splanchnic zone. Pulmonary vascular resistance increases and redistribution of blood flow to poorly ventilated areas, that is, shunting, can occur. The work of breathing increases during spontaneous respiratory activity. There is fluid retention in the body. Opening all DPs and overstretching them increases dead space (Vd). But high levels of PEEP are especially harmful in non-homogeneous lung lesions. They lead to overextension of easily recruited healthy alveoli even before the end of inspiration and a high final inspiratory volume, that is, to volume trauma and/or barotrauma.

The PEEP level established by the doctor may actually be higher due to the occurrence of auto-PEEP. This phenomenon is associated with either high Raw or insufficient exhalation time, and more often with a combination of these factors. The harmful effects of auto-PEEP are the same as with high PEEP values, but an unintended decrease in ΔP can lead to severe hypoventilation. In the presence of auto-PEEP, the risk of developing barotrauma is higher, and the sensitivity threshold of flow and pressure sensors in trigger systems is higher. The presence of auto-PEEP can only be determined using a respiratory monitor, both in absolute terms and from a flow graph. A decrease in auto-PEEP can be achieved by: using bronchodilators, reducing Vt, increasing expiratory time. In neonates with normal Raw, auto-PEEP is unlikely to occur if expiratory time is > 0.5 sec. This phenomenon is more likely to develop when the respiratory rate is > 60 per minute. With HF ventilation it always occurs, except for HFO.

Respiration rate – R ( respiratory rate).

This designation is most often found on TCPL fans. In German-made equipment, the time of inhalation and exhalation is mainly set, and the breathing frequency is a derivative. In ventilators for adult patients and in anesthesia equipment, the frequency of respiratory cycles is often designated as f (frequency).

This parameter largely determines the minute volume of respiration and the minute volume of alveolar ventilation. MV = Vt × R. MValv = R(Vt – Vd).

We can conditionally distinguish three ranges of respiratory frequencies used in newborns: up to 40 per minute, 40 – 60 per minute, which corresponds to the physiological norm, and >60 per minute. Each range has its advantages and disadvantages, but there is no consensus on the optimal breathing rate. In many ways, the choice of frequency is determined by the clinician’s commitment to certain ranges. But, ultimately, any of the selected frequencies should provide the required level of minute alveolar ventilation. It is necessary to take into account the type of pulmonary mechanics disorders, the phase of the disease, the patient’s own respiratory rate, the presence of barotrauma and CBS data.

Frequencies< 40/мин могут использоваться при вентиляции пациентов с неповрежденными легкими (по хирургическим или неврологическим показаниям), при уходе от ИВЛ, что стимулирует дыхательную активность пациента. Низкие частоты более эффективны при высоком Raw, так как позволяют увеличивать время вдоха и выдоха. В острую фазу легочных заболеваний некоторые авторы используют низкую частоту дыхания с инвертированным соотношением I:Е (для повышения МАР и оксигенации), что часто требует парализации больного и увеличивает вероятность баротравмы и снижения сердечного выброса из-за повышенного МАР.

Frequencies/min are effective in the treatment of most pulmonary diseases, however, they cannot always provide adequate alveolar ventilation.

Frequencies > 60/min are necessary when using minimal tidal volumes (4 – 6 ml/kg body weight), since this increases the role of dead space (Vd), which in addition can increase due to the capacity of the flow sensor. This approach can be successfully used in “stiff” lungs because it reduces the work of breathing to overcome elastic resistance, reduces tissue stress, reduces pulmonary vascular resistance, and reduces the likelihood of lung baro/volume injury. However, with a shortened expiratory time, there is a high probability of auto PEEP with corresponding adverse effects. The doctor may not be aware of this unless he uses a breathing monitor. The use of low Vt along with auto PEEP can lead to the development of hypoventilation and hypercapnia.

The use of frequencies 100 – 150/min (HFPPV - high frequency positive pressure ventilation) is not considered in this material.

Inhalation time – Ti( time inspiratory), expiratory time – Te( time expiratory) and

ratio Ti/ Te( I: E ratio).

The general rule when determining the minimum values ​​of Ti and Te is that they are sufficient to provide the required tidal volume and effectively empty the lungs (without the appearance of auto PEEP). These parameters depend on elongation (C) and aerodynamic resistance (Raw), that is, on TC (C × Raw).

In newborns with intact lungs, values ​​of 0.35 - 0.45 seconds are usually used for inspiration. When the compliance of the lungs decreases (RDS, pulmonary edema, diffuse pneumonia - conditions with low TC values), it is permissible to use a short inhalation and exhalation time of 0.25-0.3 seconds. In conditions with high Raw (bronchial obstruction, BPD, SAM), Ti should be extended to 0.5, and in BPD to 0.6 sec. When elongating Ti over 0.6 sec. can provoke active exhalation against instrumental inhalation. At Ti > 0.8 sec. Many authors note a clear increase in the incidence of barotrauma.

In one-year-old children, the respiratory rate is lower, and Ti increases to 0.6 - 0.8 sec.

I:E ratio. Normally, inhalation during spontaneous breathing is always shorter than exhalation, due to resistance to the expiratory flow of the glottis and a decrease in the cross-section of the bronchi, which increases Raw during exhalation. During the behavior of mechanical ventilation, these patterns are preserved, therefore, in most cases Ti< Te.

Fixed I:E values ​​are used mainly in anesthesia equipment and in some older models of TCPL ventilators. This is an inconvenience, since at a low respiratory rate the inspiratory time can be significantly longer (for example, in IMV mode). In modern fans, I:E is calculated automatically and displayed on the control panel. The I:E ratio itself is not as important as the absolute values ​​of Ti and Te.

Ventilation with an inverted I:E ratio (Ti > Te) is usually used as a last resort when oxygenation cannot be improved otherwise. The main factor in increasing oxygenation in this case is an increase in MAP without an increase in PIP.

When leaving mechanical ventilation, the respiratory rate decreases due to an increase in Te, while I:E changes from 1:3 to 1:10. For meconium aspiration, some authors recommend ratios of 1:3 – 1:5 to prevent “air traps”.

A respiratory monitor provides invaluable assistance in selecting adequate Ti and Te values ​​(especially if it determines Tc). You can optimize the Ti and Te values ​​by analyzing the flow graph in the DP on the monitor display. (Fig. 8)

Oxygen concentration – FiO 2

The partial pressure of oxygen in the respiratory mixture, and therefore the gradient Palv O2 - Pv O2, which determines the diffusion of oxygen through the alveolar capillary membrane, depends on FiO2. Therefore, FiO2 is the main determinant of oxygenation. But high concentrations of oxygen are toxic to the body. Hyperoxia causes oxidative stress (free radical oxidation) that affects the entire body. Local exposure to oxygen damages the lungs (see section VILI). The long-term consequences of the toxic effects of oxygen on the body can be very sad (blindness, CLD, neurological deficit, etc.).

Long-standing recommendations to always start mechanical ventilation of newborns with FiO2 1.0 to quickly restore oxygenation are now considered outdated. Although Order No. 000 of the city “On improving primary resuscitation care for newborns in the maternity ward” is still in force, a new one is being prepared, taking into account the results of research carried out already in the 21st century. These studies found that ventilation with pure oxygen increases neonatal mortality, oxidative stress persists for up to 4 weeks, kidney and myocardial damage increases, and neurological recovery time after asphyxia increases. Many leading neonatal centers in developed countries have already adopted different neonatal resuscitation protocols. There is no evidence that increasing FiO2 will improve the situation if the newborn remains bradycardic despite adequate ventilation. If mechanical ventilation is necessary, it is started with room air. If bradycardia and/or SpO2 persists after 30 seconds of ventilation< 85%, то ступенчато увеличивают FiO2 с шагом 10% до достижения SpO2 < 90%. Имеются доказательства эффективности подобного подхода (доказательная медицина).

In the acute phase of pulmonary diseases, it is relatively safe to perform mechanical ventilation with FiO2 0.6 for no more than 2 days. For long-term mechanical ventilation, it is relatively safe to use FiO2< 0,4. Можно добиться увеличения оксигенации и иными мерами (работа с МАР, дегидратация, увеличение сердечного выброса, применение бронхолитиков и др.).

Short-term increases in FiO2 (for example, after aspiration of sputum) are relatively safe. Measures to prevent oxygen toxicity are outlined in section VILI.

IF - inspiratory flow EF - expiratory flow

Figure 8. Optimization of Ti and Te using BF flow curve analysis.

A) Ti is optimal (the flow has time to decrease to 0). There is room for increase

respiratory rate due to the expiratory pause.

C) Ti is not enough (the flow does not have time to decrease). Increase Ti and/or PIP.

Acceptable when using minimum Vt.

C) Ti is insufficient (flow is low and does not have time to fill the lungs). Increase

breathing circuit flow and/or Ti.

D) Te is insufficient (the expiratory flow does not have time to reach the isoline, then

there is stop) Auto – PEEP. Increase Te by decreasing frequency (R).

E) Ti and Te are insufficient, neither inhalation nor exhalation has time to complete. Likely

severe bronchial obstruction. Auto – PEEP. Increase Ti and especially Te and,

perhaps PIP.

F) It is possible to reduce Ti1 to Ti2 without reducing Vt, since between Ti1 and Ti2

there is no flow in the DP unless the goal is to increase the MAP due to the PIP plateau.

There is a reserve for increasing the respiratory rate due to the inspiratory pause.

Average airway pressure – MAP( mean airway pressure).

Gas exchange in the lungs occurs both during inhalation and exhalation, so it is the MAP that determines the difference between atmospheric and alveolar pressure (additional pressure that increases the diffusion of oxygen through the alveolar capillary membrane). This is true if MAP = Palv. However, MAP does not always reflect the average alveolar pressure, which determines the diffusion of oxygen and the hemodynamic effects of mechanical ventilation. At a high respiratory rate, not all alveoli have time to ventilate sufficiently with a short inhalation time (especially in areas with increased Raw), so Palv< MAP. При высоком Raw и коротком времени выдоха Palv >MAP due to auto-PEEP. At high minute volume of respiration Palv > MAP. But under normal conditions, MAP reflects the average alveolar pressure and is therefore the second important determinant of oxygenation.

MAP is a derived parameter of TCPL ventilation, as it depends on the values ​​of the main parameters: PIP, PEEP, Ti, Te, (I:E) and the flow in the breathing circuit.

MAP can be calculated using the formula: MAP = KΔP(Ti/Te + Te) +PEEP, where K is the rate of pressure increase in the blast furnace. Since K depends on the flow rate in the patient’s circuit and the mechanical properties of the lungs, and we cannot calculate the real value of this coefficient, it is easier to understand what MAP is using a graphical interpretation (in the form of the area of ​​​​the figure that the pressure curve in the DP forms during breathing cycle Fig.9 a, c. The influence of flow, PIP, PEEP, Ti and I:E is presented in Fig. 9c, d.

Figure 9. Graphic interpretation of MAP and the influence of ventilation parameters.

Modern fans detect MAP automatically, and this information is always present on the control panel. By manipulating different ventilation parameters, we can change MAP without changing ventilation or vice versa, etc.

The role of various ventilation parameters in changing the MAP value (and oxygenation) is different: PEEP > PIP > I:E > Flow. The presented hierarchy is valid for ventilation of damaged lungs. When ventilating healthy lungs, the effect of mechanical ventilation parameters on MAP levels and oxygenation may be different: PIP > Ti > PEEP. During barotrauma, increasing MAP levels will reduce oxygenation. An increase in the respiratory rate increases the MAP, since (with other ventilation parameters remaining unchanged) the expiratory time is shortened, and therefore I:E changes.

An increase in MAP > 14 cmH2O may reduce oxygenation due to decreased cardiac output and impaired oxygen delivery to tissues. The harmful effects of high MAP levels are described above in the PEEP section (since PEEP is the one that most affects MAP levels).

Tidal volume – Vt ( volume tidal).

Tidal volume is one of the main determinants of ventilation (MOV, MOAV). With TCPL ventilation, Vt is a derived parameter, since it depends not only on the settings on the ventilator, but also on the state of the patient’s pulmonary mechanics, that is, on C, Raw and Tc. Vt can only be measured using a respiratory monitor.

If we ignore the influence of Raw, then Vt is determined by the difference between PIP and Palv at end expiration and lung compliance: Vt = C(PIP – Palv). Since, in the absence of auto – PEEP at the end of expiration, Рalv = PEEP, then Vt = CΔP. Therefore, with the same settings on the ventilator, Vt may be different in the same patient. For example: In a premature infant with RDS, Cdyn = 0.5 ml/cm H2O, PIP – 25 cm H2O and PEEP – 5 cm H2O, Vt = 0.5(25 – 5) = 10 ml. After the introduction of surfactant, after 12 hours Cdyn = 1.1 ml/cm H2O, ventilation parameters are the same, Vt = 1.1 × 20 = 22 ml. However, these calculations are very approximate, since Vt is influenced by the shape of the pressure curve, the inhalation/exhalation time, and possible turbulence in the airway. Saving ΔР = const. at different levels, PEEP will most likely change Vt, but how and by how much is difficult to predict due to the nonlinear nature of the change in extensibility. Therefore, Vt should be measured after changing any of the ventilation parameters.

Currently, the general recommendation is to maintain Vt within the physiological range of 5 – 8 ml/kg body weight, both in newborns and adults (6 – 8 ml/kg calculated ideal body weight). When ventilating healthy lungs, acceptable values ​​are 10–12 ml/kg. “Protective ventilation” (lung protective ventilation) involves the use of minimum tidal volumes of 5–6 ml/kg. This reduces tissue stress in the affected low-comtensibility lungs.

However, low-volume ventilation reduces alveolar ventilation since a significant portion of Vt ventilates dead space. This circumstance forces an increase in alveolar ventilation by increasing the respiratory rate. But at frequencies > 70/min, the minute volume of ventilation begins to decrease due to the shortening of Ti, when Paw does not have time to reach the PIP level, which reduces ΔP and Vt. And the shortening of Te causes the appearance of auto – PEEP, which also reduces ΔР and Vt. Attempts to increase ΔР by reducing PEEP are not always effective, since low PEEP values ​​contribute to the collapse of part of the alveoli and bronchioles, which reduces the respiratory surface area.

At high Raw, you can increase Vt by increasing Ti if the inspiratory flow does not have time to decrease. However, after pressure equalization (PIP = Palv), an increase in Ti will not lead to an increase in Vt. This is well monitored when analyzing the flow curve in the DP.

In children with extremely low body weight, the flow sensor increases the dead space quite significantly. In this group of patients Vt should not be< 6 – 6,5мл/кг. При гиперкапнии можно увеличить альвеолярную вентиляцию уменьшением мертвого пространства, сняв переходники, датчик потока и укоротив интубационную трубку. При проведении протективной вентиляции гиперкапния в той или иной степени имеет место всегда, но ее необходимо поддерживать в допустимых пределах (permissive hypercapnia).

Only regular blood gas studies help to fully monitor the adequacy of alveolar ventilation to the patient’s metabolic level (carbon dioxide production). In the absence of laboratory monitoring, the adequacy of ventilation can be judged by good synchronization of the patient with the ventilator (unless pain management with narcotic analgesics or anticonvulsants such as barbiturates and benzodiazepines is used). Clinical manifestations of hypocapnia and hypercapnia in newborns are practically absent, unlike in adults.

Breath monitoring allows you to track the dynamics of volume changes during the respiratory cycle (time/volume graph). In particular, it is possible to determine the leakage of Vt between the IT and the larynx (Fig. 10.).

Figure 10. Time/volume charts. A) Normal. B) Volume leakage.

Digital information allows you to determine the volume of leakage. Leakage of about 10% of the volume is acceptable. If there is no leak, the exhaled volume may exceed the inhaled volume. This is due to gas compression at high PIP values ​​and gas expansion during warming if the breathing circuit temperature is low.

REGULATION OF BREATHING DURING VENTILATION AND INTERACTION

PATIENT WITH FAN.

Most newborns do not stop breathing on their own during mechanical ventilation, since the work of their respiratory centers (in the medulla oblongata - PaCO2, cerebellar olives - cerebrospinal fluid pH, in the carotid sinuses - PaO2) does not stop. However, the nature of the response to changes in blood gas composition and pH is highly dependent on gestational age and postnatal age. The sensitivity of the chemoreceptors of the respiratory centers is reduced in premature infants, and hypoxemia, acidosis, hypothermia, and especially hypoglycemia further reduce it. Therefore, during hypoxia of any origin, respiratory depression quickly develops in premature infants. This central hypoxic depression usually resolves by the third week of the postnatal period. Full-term newborns respond to hypoxia with shortness of breath, but later respiratory depression may occur due to fatigue of the respiratory muscles. A decrease in MVR in response to an increase in FiO2 in full-term infants develops on the second day of life, and in premature infants in the second week. Barbiturates, narcotic analgesics and benzodiazepines cause respiratory depression, the greater the lower the gestational age and postnatal age.

There is a feedback between the respiratory center and changes in lung volumes, which is provided by the Hering-Breuer reflexes, which regulate the ratio of the frequency and depth of breathing. The severity of these reflexes is maximum in full-term infants, but decreases with age.

1). Inspiratory inhibitory reflex:

Inflating the lungs during inhalation stops it prematurely.

2). Expiratory-facilitating reflex:

Inflating the lungs during exhalation delays the onset of the next inhalation.

3). Lung collapse reflex:

A decrease in lung volume stimulates inspiratory activity and

shortens exhalation.

In addition to the Hering-Breuer reflexes, there is the so-called Guesde paradoxical inhalation reflex, which consists of deepening one’s own inhalation under the influence of a mechanical one, but it is not observed in all children.

The interstitium of the alveolar walls contains so-called “J” receptors, which are stimulated by overdistension of the alveoli (for example, with Ti > 0.8 sec), causing active exhalation, which can cause barotrauma. “J” receptors can be stimulated by interstitial edema and pulmonary capillary congestion, leading to the development of tachypnea (particularly TTN).

Thus, it is possible to observe 5 types of interaction between the patient and the ventilator:

1). Apnea is most often associated with hypocapnia (hyperventilation), severe

CNS damage or drug-induced depression.

2).Inhibition of spontaneous breathing under the influence of Hering-Breuer reflexes.

3). Stimulation of spontaneous breathing.

4). The patient's exhalation versus mechanical inhalation is a “fight” with the ventilator.

5). Synchronization of spontaneous breathing with mechanical ventilation.

The presence of spontaneous breathing during mechanical ventilation is a useful factor, since:

1). Improves V/Q.

2). Trains the respiratory muscles.

3). Reduces the adverse effects of mechanical ventilation on hemodynamics, ICP and cerebral

blood flow

4). Corrects blood gas composition and pH.

Based on the above, the optimal ventilation modes are those that allow synchronizing the operation of the patient and the ventilator. In the initial phase of treating a patient, it is permissible to suppress his respiratory activity by hyperventilation, however, one should remember about its adverse effect on cerebral blood flow. CMV (control mandatory ventilation) - controlled forced ventilation should be used for apnea of ​​any origin and hypoventilation (hypoxemia + hypercapnia). Its use is also justified to reduce the patient's increased work of breathing (and systemic oxygen consumption) in severe DN. In this case, however, it is necessary to suppress respiratory activity by hyperventilation, sedation and/or myoplegia.

Although CMV can quickly and effectively restore gas exchange, it has significant disadvantages. The disadvantages of CMV include: the need for constant, strict control of oxygenation and ventilation, since the patient cannot control them, decreased cardiac output, fluid retention in the body, wasting of the respiratory muscles (with long-term use), hyperventilation can cause bronchospasm. The total duration of mechanical ventilation when using CMV increases. Therefore, CMV should be used as a forced and, preferably, short-term measure.

As the patient's condition improves, ventilatory support should be gradually reduced. This stimulates his respiratory activity, allows him to partially control gas exchange and train the respiratory muscles. Measures to reduce ventilation support can be carried out in different ways. The choice of method depends on the capabilities and quality of the breathing equipment used and the experience of the doctor.

The simplest solution is to use the IMV (intermittent mandatory ventilation) mode - intermittent forced ventilation. This mode does not require the use of complex breathing equipment (any type is suitable) and consists of a gradual reduction in the frequency of mechanical breaths. Between mechanical breaths, the patient breathes spontaneously using a continuous flow in the breathing circuit. MOD is only partially controlled by a doctor. This poses a certain danger due to irregular breathing activity and requires the attention of personnel. With good respiratory activity and a gradual decrease in the frequency of mechanical breaths, the MOD gradually comes under the complete control of the patient.

ST. PETERSBURG STATE
PEDIATRIC MEDICAL UNIVERSITY
RECRUITMENT MANEUVER IN
PEDIATRIC PRACTICE.
WHEN AND HOW?
Aleksandrovich Yu.S.
Head of the Department of Anesthesiology, Reanimatology and
emergency pediatrics AF and DPO

THE CONCEPT OF “OPEN LUNGS” (OL).
Consists of opening (PIP) collapsed affected areas
lungs (alveoli), and maintaining (PEEP) them open
state during all phases of breathing (inspiration and
exhalation).
It is important to prevent collapse
lungs (PEEP).
BENEFITS: improved arterial oxygenation
blood, which was caused by an increase in the fraction
intrapulmonary shunt and decreased pulmonary compliance
by shifting the slope of the P/V curve to a higher point
effectiveness and prevention of cyclic
opening/collapse of the alveoli with each respiratory cycle.
Lachmann B. Open up the lung and keep the lung open. Intensive Care Med 1992; 18:319– 3 2 1

OPEN LUNG STRATEGY CONCEPT

Recruitment maneuver is a method of respiratory therapy,
aimed at increasing the number of alveoli,
involved in ventilation (F.J.J. Halbertsma et al.,
2007)
Alveolar mobilization maneuver – respiratory strategy
support,
consisting
V
short-term
step-by-step increase in average pressure in the respiratory
ways
3

RECRUITMENT MANEUVER

This is a deliberate dynamic process
temporary increase in transpulmonary
pressure, the purpose of which is to open
unstable airless
(collapsed) alveoli.
(Ppl): Pl = Palv - Ppl.
Yu. V. Marchenkov, V. V. Moroz, V. V. Izmailov Pathophysiology of recruiting ventilation and its
influence on the biomechanics of breathing (literature review). Anesthesiology and Reanimatology No. 3, 2012
p.34-41.

The lower parts of the lungs are bad
ventilated at end expiration
due to compression
hydrostatic pressure. IN
at the end of inspiration, open alveoli
may overstretch (A),
excess voltage may
be generated at the border
between ventilated and
unventilated areas
lungs (B), and the lower alveoli
may reopen and
close, which leads to
tissue damage (C).

Three fan mechanisms
induced lung injury
(VILI):
a) excessive stretching of the tissue,
caused by excessive volume and
pressure,
b) alveolar collapse and
re-opening every time
inhalation, secondary to
deactivation of surfactants
substances that cause dynamic
tissue injury caused
deformation
c) Heterogeneous ventilation, with
which isolated
areas of alveolar collapse
(blue arrows), violates
alveolar stability
interdependence.

RECRUITABILITY

An ideal model reflecting the consequences of increased permeability in conditions
increase in pressure, with the coexistence of heterogeneous AREAS
HYPERINFLATION, NORMAL INFLATION, COLLAPSE AND AREAS
CONSOLIDATION. The arrows indicate the pressure required to open these zones.
∞ represents infinite pressure, i.e. this area can never be
open despite the increase in positive pressure in the AP.
Umbrello M, Formenti P, Bolgiaghi L, Chiumello D. Current Concepts of ARDS: A Narrative Review. Int J Mol Sci. 2016 Dec
29;18(1).

RECRUITABILITY

Example of a CT scan of the lungs in patients with high (top panel) or low (bottom panel)
recruitment potential. Arrows indicate changes in morphological
states at low pressure in the DP (5 cm H2O), and high pressure in the DP (45 cm H2O)
Umbrello M, Formenti P, Bolgiaghi L, Chiumello D. Current Concepts of ARDS: A Narrative Review. Int
J Mol Sci. 2016 Dec 29;18(1).

DEVELOPMENT OF ATELECTASIS IMMEDIATELY AFTER INDUCTION OF ANESTHESIA

CT scan of the chest showing the patient's lungs before (left) and after (right) induction
anesthesia. On the left, the pulmonary fields in the posterior section are clearly visible. On the right you can see the presence
atelectasis in the back of the lungs (surrounded by a red oval).
Hedenstierna G. Effects of anesthesia on respiratory function. Bailliere's
Clin Anaesthesiol. 1996;10(1):1-16.

NEGATIVE EFFECTS OF GENERAL ANESTHESIA ON RESPIRATORY FUNCTION

REASONS FOR THE DEVELOPMENT OF ATELECTASIS:
(1) muscle relaxation,
(2) increase (FiO2),
(3) suppression of sigh.

Laplace's Law (1806)

Laplace's law explains
increase in PaO2:
P = 2T/r
where P denotes pressure (in this case PaO2); T surface tension; r, radius.
When the alveolar radius decreases in atelectasis, the pressure
required to fill the alveoli increases. MRA
provide the high pressure necessary for repeated
mobilization of collapsed alveoli.

SIGH REFLEX

In 1964, Bendixen et al2 found that awake
men and women sigh on average about 9 and 10 times per hour.
The sigh reflex is a normal homeostatic reflex.
Reflex influences from irritant receptors (located
in the subepithelial space of the respiratory tract and
perform the function of both mechano- and chemoreceptors). IN
under normal conditions, irritant receptors are excited when
decreased pulmonary ventilation, and in this case lung volume
decreases. In this case, irritants are excited
receptors that cause forced inhalation ("sigh").
Sighing minimizes alveolar-arterial (A-a)
oxygen tension gradient.
Sigh releases new portions of surfactant
substance and distributes it evenly on the alveolar
surfaces in the distal airways.
Bendixen H.H., Smith G.M., Mead J.Pattern of ventilation in young adults. J Appl Physiol. 1964
Mar;19:195-8.

SIGH REFLEX

In 1964, Bendixen et al hypothesized that
constant ventilation with adequate but static
tidal volumes in anesthetized patients
leads to progressive atelectasis and increased
shunt when there are no sighs.
They showed that on average the oxygen pressure
arterial blood falls by 22%, and pulmonary compliance
by 15% in the absence of sighs.
After several minutes of slow, deep,
steady breathing, oxygen pressure in
arterial blood increased by an average of 150 mm Hg.
Art., reducing the shunt created by the static DO.

"RO-5" is a volumetric respirator,
intended for carrying out
long-term automatic artificial and
assisted ventilation during
anesthesia or resuscitation. Unlike RO-3,
the RO-5 device allows you to change
the ratio of inhalation and exhalation within
1:1,3; 1:2 and 1:3; adjust parameters
breathing within a wider range; more
convenient to set the tidal volume,
perform manual ventilation with
using open, semi-open and
semi-closed respiratory systems. In it
there is a gas jet suction,
DEVICES FOR
AUTOMATIC PERIODIC
DEVELOPMENT OF THE LUNGS, as well as for
providing auxiliary ventilation
lungs. RO-5 is equipped with an anesthetic
block type "Narkon-P".

To whom?

General anesthesia
Hypoxemic ARF (ARDS)
After the reorganization of the LDP

CLINICAL CONDITIONS ASSOCIATED WITH ARDS IN CHILDREN

Zimmerman JJ, Akhtar SR, Caldwell E, Rubenfeld GD. Incidence and outcomes of pediatric acute lung injury.
Pediatrics. 2009;124(1):87-95.
Dahlem P, van Aalderen WM, Hamaker ME, Dijkgraaf MG, Bos AP. Incidence and short-term outcome of acute
lung injury in mechanically ventilated children. Eur Respir J. 2003;22(6):980-5.

WHEN? ANALYSIS OF INDICATIONS FOR RECRUITMENT (F.J.J. Halbertsma et al., 2007)

Pathological
state
Pediatric
ICU
Neonatal
ICU
Inadequate
oxygenation
88%
85%
Atelectasis
50%
43%
High performance
FiO2
25%
43%
States,
leading to
decrease in PEEP
(depressurization
circuit, sanitation of LDP)
80%
46%
183.1 Traditional ventilation modes.
3.1.1 There is no data on the effect of mechanical ventilation on patient outcomes
patients with PARDS.
3.2.1 Tidal volume
For any controlled ventilation in children, use BEFORE
range of physiological values ​​for age/body weight
(i.e. 5-8 ml/kg body weight predicted) depending on
pathologies of the lungs and compliance of the respiratory system.
3.2.2 Use DO for each specific patient in
depending on the severity of the disease. UP TO 3-6 ml/kg
estimated body weight for patients with low compliance
respiratory system and closer to the physiological range (5-8 ml/kg ideal body weight) for patients with
more preserved compliance of the respiratory system.
3.2.3 Plateau pressure limitation
In the absence of measurement capability
transpulmonary pressure, plateau pressure limit at
inhalation 28 cmH2O and higher plateau pressures (29-32cm
H2O) in patients with increased chest stiffness
(i.e., decreased chest wall compliance).
The Pediatric Acute Lung Injury Consensus Conference Group, 20153.3 PEEP/Mobilization Maneuvers
alveoli
3.3.1 Moderate increase in PEEP (10-15
cm H2O). Titrate under oxygenation and hemodynamic control
reactions in patients with severe PARDS.
3.3.2 PEEP levels greater than 15 cmH2O may be necessary when
severe PARDS, but attention should be paid to
plateau pressure limitation!!!
3.3.3 Markers of oxygen delivery and respiratory compliance
systems, and hemodynamics should be carefully monitored during
increasing PEEP.
3.3.4 Clinical studies should be conducted to evaluate
the impact of elevated PEEP on outcome in the pediatric population.
3.3.5 Use caution when using maneuvers
mobilization of the alveoli in an attempt to improve
oxygenation slowly step by step
increasing and decreasing PEEP. Maneuvers
prolongation of inhalation cannot be recommended
due to lack of available data.
The Pediatric Acute Lung Injury Consensus Conference Group, 2015

RECRUITMENT METHODS

21

MAXIMUM AIRWAY PRESSURE VALUES GENERATED DURING A RECRUITMENT MANEUVER (F.J.J. Halbertsma et al., 2007)

Parameter
Pediatric
ICU
Neonatal
ICU
Positive
end pressure
exhalation, cm H2O
28.3±7.5
9.2 ±1.1
Positive
inspiratory pressure,
cmH2O
46.7±12.1
35.8±4.9
22

Pressure-volume curves for healthy lungs (left) and ARDS (right)

In ARDS, lung damage leads to a decrease in compliance, FRC is reduced, and the curve
"volume-pressure" is shifted to the right. The use of PEEP in ARDS, when reduced
lung compliance allows you to keep the pressure-volume curve in an advantageous position, i.e. like this
so that the tidal volume oscillates between the lower and upper inflection points.

PHYSIOLOGICAL BASES OF RECRUITMENT MANEUVER

24

CT CT OF THE LUNGS OBTAINED FROM CURVE TRACING UNDER STATIC CONDITIONS

Recruitment begins only above the lower inflection point (LIP) on the inspiratory curve and
continues to maximum pressure even above the upper inflection point (UIP).
Derecruitment begins when the pressure in the DP decreases to its maximum point
curvature (PMC) and continues throughout the rest of the expiratory curve.

Indicator
Characteristic
Age, g
4,8 (1-14)
Number of boys
11 (52%)
Primary RDS
15 (71%)2
Aspiration
pneumonia
2 (13%)
Infectious
pneumonia
11 (73%)
Drowning
2 (13%)
Secondary RDS
6 (29%)
Sepsis
4 (66%)
Application of AIC
2 (33%)
1 vertical bar = 1 stage of maneuver,
which lasted 1 minute

1. Sedation, analgesia and myoplegia
2. Positive inspiratory pressure (PIP) =
15 cm H2O from PEEP = constanta
3. Starting level PEEP = 8 cm H2O
4. Step by step increase in PEEP by 2 cm H2O
every minute until reaching
maximum pressure in the respiratory
paths (PIP + PEEP) = 45 cm H2O or
reducing compliance indicators
5. Gradual step-by-step reduction of 2 cm
H2O every minute until pressure is reached
critical point of alveolar closure
6. Selection of the optimal level PEEP =
critical closing point pressure
alveoli + 2 cm H2O
7. Repeating the maneuver
recruitment to achieve pressure
opening of the alveoli (within 2 minutes) with
subsequent correction of ventilation parameters

a – the differences are statistically significant (p<0,05) по сравнению с показателями до маневра б – различия статистически значимы (р<0,01) по сравнению с по

RESPIRATORY SUPPORT INDICATORS
TIME OF MANEUVER
Indicator
To
maneuver
After
maneuver
In 4 hours
after the maneuver
In 12 hours
after the maneuver
Average pressure in
respiratory tract, cm
H2 O
14
(11-17)
13
(10-19)
13
(11-17)
13
(11-15)
Maximum pressure in
respiratory tract, cm
H2O
31
(25-36)
29
(23-33)
26a
(21-30)
26a
(21-29)
Dynamic compliance
lungs, ml/cm H2O
8
(3-12)
9
(2-11)
5
(2-14)
5
(3-14)
Respiration rate
date/minute
24
(20-29)
21
(18-28)
29b
(27-35)
29b
(25-33)
Oxygen concentration
in the respiratory mixture, %
0,6
(0,45-0,65)
0.6a
(0,5-1,0)
0,5
(0,45-0,6)
0,5
(0,4-0,6)
A
b
<0,05) по сравнению с показателями до маневра
– the differences are statistically significant (p<0,01) по сравнению с показателями до маневра

IO = (MAP x FiO2 x 100%)/PaO2

Alveolar mobilization maneuver in children with SOPL/ARDS
helps improve oxygenation and has
positive effect on gas exchange rates in
within 12 hours after it is carried out

Alveolar recruitment maneuver in mechanical ventilation pediatric intensive care unit children Neves V.C., Koliski A., Giraldi D.J. Rev Bras Ter Intensiva. 2009; 21(4):453-460

1.
Sedation, analgesia and
myoplegia
2. Positive pressure on
inhalation (PIP) = 15 cm H2O from PEEP
= constanta
3. Starting level PEEP = 10
cm H2O
4. Step by step increase in PEEP
by 5 cm H2O every two minutes
until reaching the maximum
airway pressure
(PIP + PEEP) = 50 cm H2O
5. Gradual step by step
decrease by 5 cm H2O every
two minutes to reach
baseline = 10 cm H2O

MONITORING:HR,
invasive blood pressure, SaO2,
and breathing mechanics.
Continuous infusion
midazolam (1.5–5
mg/kg/min) and fentanyl
(1–3 mg/kg/h) to
achieve a score of 17-26
points on the scale
COMFORT.
20 minutes before PM
preoxygenation 100%
O2 for 5 minutes.
Vecuronium (0.1 mg/kg).

PEEP MR and titration protocol
Start with 10 cm H2O PEEP, maintaining constant inflation pressure - 15
cm H2O. MR is carried out sequentially with an increase in PEEP of 5 cm H2O
every 2 minutes until 25 cm H2O PEEP is reached. PEEP titration is based on
assessment of gasometry and lung mechanics.

Conclusions: RM is safe and good
tolerated hemodynamically
stable children with ARDS.
RM and step-by-step selection of PEEP parameters
may improve lung function in
patients with ARDS and severe hypoxemia.

Among 2,449 children,
taking part in
analysis, 353 patients (14%)
received HFOV, of which 210
(59%) - HFOV started in
within 24-48 hours after
intubation. Early
the use of HFOV was
associated with greater
duration of mechanical ventilation
(risk ratio 0.75; 95%
CI, 0.64–0.89; p = 0.001), but not
with mortality (ratio
odds, 1.28; 95% CI, 0.921.79; P = 0.15), compared to
CMV/late HFOV.

All before randomization
children were on mechanical ventilation with
FiO2 -1, PEEP 12 cm H2O,
received infusion
maintenance therapy
high central venous pressure (range from 8
up to 12 mm Hg Art.) and mostly
on inotropic and
vaspressor support in
RM time during mechanical ventilation or
HFOV. All the children were
sedated and
relaxed.

We used a SensorMedics oscillator (3100A/B) (VIASyS, USA).
The piston was stopped while the child breathed into the CPAP.
Started with MAP (average airway pressure) 30 cm
H2O (or 35 cmH2O for children with BW > 35 kg), continuous
tensile pressure was maintained for 20 s (or 30 s
for children with body weight > 35 kg).
Then, the piston was started and the MAP was gradually brought to
target level (+ 5-8 cmH2O above previous MAP at
convection ventilation). Other fan settings
adjusted based on clinical experience. Initial
parameters ΔP (amplitude of oscillatory oscillations) were
set at 3 × MAP with convection mechanical
ventilation, and the frequency was set according to age.
FiO2 was gradually reduced in stages to maintain SpO2
above 92%. RM was repeated if SpO2 was below 95% at 100% FiO2
From 1. Arterial blood gases were taken 1 hour after the maneuver.

Ventilators were used in 9 children in the CV group
Servo I or Bennett 840. RM protocol
combined with HFOV or CV in all
studied patients (used 15-20 cm
H2O PEEP, expansion pressure 20 cm H2O, with
decreasing PEEP after 2 min, titrating step by step
to achieve the best fit
parameters. Then set PEEP to + 2 cm
H2O above this level, and reduced PIP to
achieve a level of UP to 6-8 ml/kg).
Baseline clinical characteristics,
oxygenation, hemodynamic parameters and
clinical results were recorded during
procedures and 1, 4, 12, 24 and 48 hours after RM.

There was significant
increase in PaO2/FiO2 (119.2 ± 41.1,
49.6 ± 30.6, P = 0.01 *) after 1 hour
RM with HFOV versus CV.
The study showed
advantage of HFOV
compared to CV at RM
in children with severe
ARDS. Essential
influence on
hemodynamic
parameters are not
revealed. Serious
complications noted
there wasn't.

INCLUSION CRITERIA:
Performing radical surgery for congenital heart disease
No history of heart surgery
PA sBP ≥ 25 mmHg, established by ECHO-CG or angiocardiography and
confirmed intraoperatively invasive into the LA after opening the pericardium and before
performing other surgical procedures

STARTING PARAMETERS OF VENTILATION
Ventilation in pressure control mode (Nikkei vent.)
UP TO 7-10 ml/kg
PEEP 5 cm H2O
Inhalation to exhalation ratio 1:2
RR for monitoring PaCO2 in arterial blood with
target value 35-45 mmHg
Routine monitoring of exhaled CO2 was used
Catheters were inserted into the femoral artery and
internal jugular vein

One of the stages of the operation involves complete
disconnecting the patient from the ventilator and
depressurization of the circuit
After completing manipulations with the heart, the lungs
straightened out with three to five manual breaths with
peak pressure of 40 cm H2O
Mechanical ventilation continued for
starting parameters before applying skin
sutures, hemodynamics stabilized
the use of milrinone and norepinephrine,
included in the standard operation protocol, after
why the recruitment maneuver was used

MANEUVER METHOD
MR was performed in 3 stages, each
lasts 30 seconds:
At stage 1 PIP up to 30 H2O and PEEP up to
10 cm H2O
At stage 2 only PEEP up to 35 cm
H2O
At stage 3, PEEP was reduced to 15 cm
H2O
The intervals between stages lasted
1 minute each, for stabilization
ventilation parameters

Significant PA SBP was observed during
during stages 2 and 3 of MR, but after
completion of the maneuver was observed by him
reduction to initial values.
No violations were observed
breathing or hemodynamics, there was no
pressure crises in aircraft
Intact pleural
cavity was present in 5 patients (50%), according to
Rg data from the ICU, in all patients
the lungs were straightened and had
homogeneous structure, without data for
pneumothorax or atelectasis.
Ventilation lasted an average of 23 hours
(from 5 to 192 hours)

SI- extended inflation CPAP 40 cm H2O for 40 sec + selection of PEEP,
SRS – stepwise recruitment strategy - pressure 15 cmH2O above
PEEP. Attention should be paid to PaCO2.

51 newborns
1.
2.
3.
4.
1.
2.
3.
4.
gestation period 28-32 weeks
weight more than 1000 g
RDS
traditional mechanical ventilation from birth
Exclusion criteria:
the predicted duration of mechanical ventilation is less
24 hours;
ENMT;
duration of illness more than 72 hours;
VPR, SUV, PP CNS.
50

PATIENT CHARACTERISTICS

Group I
Relief of arterial
hypoxemia with the use
recruitment maneuver
alveoli
Group II
Relief of arterial
hypoxemia without use
recruitment maneuver
alveoli
n = 24
Boys 15
Girls 9
body weight 1343 g (1060-1540)
Apgar 1 = 4.8 (4.0-6.0)
Apgar 5 = 5.7(5.0-6.0)
n =27
Boys 16
Girls 11
body weight 1801 g (1500-2080)
Apgar 1 = 5.4 (5.0-7.0)
Apgar 5 = 5.9 (5.0-7.0)
91.6%(22) – endotracheal
surfactant administration
(“Curosurf”, 200 mg/kg).
81.5%(22) – endotracheal
surfactant administration
(“Curosurf”, 200 mg/kg).
66.7%(16) - antenatal
prevention (Dexon, 24 mg)
66.7%(18) - antenatal
prevention (Dexon, 24 mg)
51

RESPIRATORY SUPPORT

Parameter
Group I
Group II
Oxygen fraction in the breathing mixture, %
48,6 (45-50)
45 (40-55)
Positive inspiratory pressure, cm H2O
17,4 (16-18)
18 (17-18)
5,0 (4-5)
4,0 (3,0-4,0)
37 (34-40)
36 (30-40)
0,3 (0,28-0,31)
0,32 (0,3-0,34)
12 (11-12)
11 (9-13)
Positive end-expiratory pressure, cm
H2O
Respiration rate, number/minute
Inhalation time, s
Average pressure in the respiratory tract, cmH2O
"Babylog 8000+" (Draeger, Germany),
"Servo I" (Maquet, Sweden),
"Hamilton-G5" (Hamilton Medical, Switzerland)
52

METHODOLOGY

Setting PEEP at the lowest point
inflection of the pressure-volume curve
Volume
Stepwise increase in PIP until normalization
pressure-volume curve shapes
Increase PEEP to LIP+2 cmH2O
Step by step reduction of PIP
Achieving PIP starting indicators
Pressure
Step by step reduction of PEEP
53

INDICATORS OF RESPIRATORY SUPPORT AND BIOMECHANICS AT DIFFERENT STAGES OF MANEUVER

Indicator
And
FiO2
%
RaO2
mmHg
PIP, cm H2O
PEEP, cm H2O
Сdyn, ml/cm2
Delta P
(PIP-PEEP)
BEFORE exhaling
ml/kg
Stage I
Stage II
Stage III
Stage IV
Stage V
Stage VI
47,8
(40-50)
47,8
(40-50)
47,8
(40-50)
36,4
(30,5-41,7)
58,8
(42,7-74,3)
97,8
(55,7-138,5)
68,2
(50,9-85,5)
58,5
(39,2-77,8)
53,5
(44,1-62,9)
16,9
(16-18)
16,8
(16-18)
24,7*
(22,5-26,9)
16,9
(16-18)
16,9
(16-18)
16,9
(16-18)
4,7
(4-5)
6,7
(6,2-7,3)
6,7
(6,2-7,3)
8,7
(8,2-9,3)
6,7
(6,2-7,3)
6,7
(6,2-7,3)
0,48
(0,37-0,61)
0,48
(0,37-0,61)
0,89
(0,8-0,96)
1,45*
(1,08-1,8)
1,63
(1,36-2,5)
1,54*
(1,14-1,94)
12,2
(11-13)
12,2
(11-13)
18*
(17-19)
10,2
(9,0-12)
10,2
(9,0-12)
25,8*
(21-30)
5,1
(3,2-5,5)
6,5*
(4,6-7,6)
Inhalation time, s
0,3
0,3
0,3
0,3
0,3
0,3
f, number/minute
37
(35-40)
37
(35-40)
37
(35-40)
37
(35-40)
37
(35-40)
37
(35-40)
MAP, cm H2O
12,1
(11-13)
12,1
(11-13)
13,1
(12,7-13,6)
13,1
(12,7-13,6)
8,7
(8-9,5)
8,7*
(8-9,5)

COMPLICATIONS

HYPOTENSION (12%). Two mechanisms of instability
hemodynamics: firstly, an increase in pressure in
airways leads to a decrease
venous return and preload of the right
ventricle Second, an increase in alveolar
pressure, in turn causes an increase
pulmonary vascular resistance and
right ventricular afterload.
DESATURATION (9%)
BAROTRAUMA (1%).
Fan E, Wilcox ME, Brower RG, Stewart TE, Mehta S, Lapinsky SE, et al. Recruitment maneuvers for acute
lung injury: a systematic review. Am J Respir Crit Care Med. 2008;178(11):1156-63.

MAIN CONTRAINDICATIONS

hemodynamic instability (hypotension),
excitation,
chronic obstructive pulmonary disease,
unilateral lung diseases,
previous pneumonectomies,
bronchopleural fistulas,
Hemoptisis (blood in the sputum),
undrained pneumothorax,
intracranial hypertension
and long-term mechanical ventilation
Borges JB, Okamoto VN, Matos GF, Caramez MP, Arantes PR, Barros F, et al. Reversibility of lung
collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med.
2006;174(3):268-78.
Gaudencio AMAS, Barbas CSV, Troster EJ, Carvalho. Recrutamento pulmonar. In: Carvalho WB,
Hirschheimer MR, Proenza Filho JO, Freddi NA, Troster EJ, editores. Ventilazgo pulmonar mecвnica
em neonatologia e pediatria. 2a ed. Sgo Paulo: Atheneu; 2005. p. 33-40.

CONCLUSIONS

The maneuver is most effective when
early stages of ARDS.
Longer alveolar stabilization time
achieved if control is exercised
pressure and downward titration is applied
PEEP.
No evidence of effectiveness from use
RM to improve prognosis in ARDS and, in patients
with severe hypoxemia. Required
individual approach to each child.

(Continuous positive pressure ventilation - CPPV - Positive end-expiratory pressure - PEEP). In this mode, the pressure in the airways during the final phase of exhalation does not decrease to 0, but is maintained at a given level (Fig. 4.6). PEEP is achieved using a special unit built into modern respirators. A large amount of clinical material has been accumulated indicating the effectiveness of this method. PEEP is used in the treatment of ARF associated with severe pulmonary diseases (ARDS, common pneumonia, chronic obstructive pulmonary diseases in the acute stage) and pulmonary edema. However, it has been proven that PEEP does not reduce and may even increase the amount of extravascular water in the lungs. At the same time, the PEEP mode promotes a more physiological distribution of the gas mixture in the lungs, reducing venous shunt, improving the mechanical properties of the lungs and oxygen transport. There is evidence that PEEP restores surfactant activity and reduces its bronchoalveolar clearance.

Rice. 4.6. Ventilation mode with PEEP.
Airway pressure curve.

When choosing the PEEP mode, you should keep in mind that it can significantly reduce CO. The higher the final pressure, the more significant the effect of this regime on hemodynamics. A decrease in CO can occur at a PEEP of 7 cm water column. and more, which depends on the compensatory capabilities of the cardiovascular system. Increasing pressure to 12 cm water column. contributes to a significant increase in the load on the right ventricle and an increase in pulmonary hypertension. The negative effects of PEEP may largely depend on errors in its use. You should not immediately create a high level of PEEP. The recommended initial PEEP level is 2-6 cm of water column. Increasing end-expiratory pressure should be carried out gradually, “step by step” and in the absence of the desired effect from the set value. Increase PEEP by 2-3 cm of water column. no more than every 15-20 minutes. PEEP is especially carefully increased after 12 cm of water column. The safest level of the indicator is 6-8 cm of water column, but this does not mean that this mode is optimal in every situation. With a large venous shunt and severe arterial hypoxemia, a higher level of PEEP with a VFC of 0.5 or higher may be required. In each specific case, the PEEP value is selected individually! A prerequisite is a dynamic study of arterial blood gases, pH and central hemodynamic parameters: cardiac index, filling pressure of the right and left ventricles and total peripheral resistance. In this case, the compliance of the lungs should also be taken into account.
PEEP promotes the “opening” of non-functioning alveoli and atelectatic areas, resulting in improved ventilation of alveoli that were insufficiently ventilated or not ventilated at all and in which blood shunting occurred. The positive effect of PEEP is due to an increase in the functional residual capacity and compliance of the lungs, an improvement in ventilation-perfusion relationships in the lungs and a decrease in the alveolar-arterial oxygen difference.
The correctness of the PEEP level can be determined by the following main indicators:
no negative effect on blood circulation;
increased lung compliance;
reduction of pulmonary shunt.
The main indication for PEEP is arterial hypoxemia, which is not eliminated by other modes of mechanical ventilation.

Characteristics of ventilation modes with volume regulation:
the most important parameters of ventilation (DO and MOB), as well as the ratio of the duration of inhalation and exhalation, are established by the doctor;
precise control of the adequacy of ventilation with the selected FiO2 is carried out by analyzing the gas composition of arterial blood;
established ventilation volumes, regardless of the physical characteristics of the lungs, do not guarantee optimal distribution of the gas mixture and uniform ventilation of the lungs;
To improve ventilation-perfusion relationships, periodic inflation of the lungs or mechanical ventilation in the PEEP mode is recommended.

78 Part II. Basic modern

more than 2-3 cm water column. It is recommended to set the initial PEEP at a level of 5-6 cm of water column. The higher the PEEP, the smaller the amount it can be increased (with PEEP > 7 - 8 cm water column - no more than 1-2 cm water column). After changing PEEP for 25-30 minutes, the doctor should assess the patient's condition, after which, if necessary, it is permissible to increase or decrease PEEP again.

On the other hand, in no case should you sharply reduce PEEP - this can cause swelling of the mucous membrane of the bronchioles and increased bronchosecretion. In addition, abrupt withdrawal of PEEP can lead to the appearance of exudate in the pleural cavity. Reducing PEEP should be done gradually and never to zero. A typical mistake when weaning a patient from mechanical ventilation is to reduce PEEP to 2-3 cm H2O. At the same time, during spontaneous attempts to inhale, the pressure in the respiratory tract becomes negative (relative to atmospheric pressure), which contributes to the development of edema of the bronchial mucosa, increased coughing, increased airway resistance, patient discomfort and, in general, delays the process of “weaning” from Ventilation Practice has shown that until the very end of the MVL it is necessary to maintain PEEP at least 4-5 cm of water column. (“physiological” PEEP), using all its positive effects.

So, when selecting the “optimal” PEEP, it is necessary to focus on the following criteria (13, 15, 109, 151):

1. Patient oxygenation according to data Sa0 2, Pa0 2, Pv0 2, Sv0 2 and Fi0 2 . As a rule, against the background of nontoxic figures Fi0 2 as PEEP increases, they increase

Sa02 and Pa02. You need to strive to maintain Sa02 > 90-92% and Pa02

> 65-70 mm Hg. against the background of Fi02< 60 %; по возможности (если позво­

depends on hemodynamics) - Sa02 > 95%, Pa02 > 70 mm Hg. at Fi02 no more

50%. Simultaneously with the growth of Sa02 and PaO, PaCO2 may also increase, but from the point of view of the principle of “permissive hypercapnia” (see p. 108, as well as pp. 243-244) this is permissible. If the PEEP increases to 10 cm water column. does not lead to the desired result, it is necessary to change the ventilation mode and/or parameters (for example, switch to pressure-controlled ventilation, increase the inspiratory time, etc.). An increase in Pv02 and Sv02 (within normal limits) is also a sign of improved oxygenation with an increase in PEEP. A decrease in the dynamics of the level of Pv02 and Sv02 (especially below 30 mm Hg and 65%, respectively) against the background of an increase in PEEP indicates possible hemodynamic disturbances. It goes without saying that when assessing oxygenation parameters, other factors affecting gas exchange should be taken into account (for example, airway patency, timely sanitation of the tracheobronchial tree, the likelihood of leakage from the respiratory circuit, etc.).

2. Oxygenation coefficient Ra0 2 / Fi0 2 > 200-250.

3. Compliance of the lungs. PEEP can be increased as long as the compliance (static compliance) of the lungs increases. If, with the next increase in PEEP, compliance decreases, it is necessary to return to the previous value. It should be borne in mind that, as a rule, an increase in PEEP above 12-14 cm of water column. no longer contributes to a further increase in lung compliance.

4. Hemodynamics. The increase in PEEP is stopped when arterial hypotension and tachycardia (bradycardia) develop, and the patient’s volume status must be assessed. If hypovolemia is diagnosed, additional infusion therapy is indicated, after which

Chapter 4. Pr zero ventilation 79

an increase in PEEP is again possible. If there is a need for high PEEP, additional infusion therapy is carried out, as a rule, even in normovolemia. If there are contraindications to additional infusion (hypervolemia, acute renal failure, heart failure), titration of inotropic drugs (for example, dopamine at a rate of 4-8 mcg/kg/min) is established. After hemodynamic stabilization, PEEP is increased if necessary. If there is the possibility of invasive or non-invasive assessment of CHD, then after each increase in PEEP over time, the data of the IOC, SI, UI and LVDP should be assessed.

5. Degree of intrapulmonary blood shunting(Qs/Qt) less than 15%. Assessed if it is possible to invasively determine central hemodynamics and oxygen transport using a catheter Swan-Ganz in the pulmonary artery.

6. Difference PaS02 -ETS02 no more than 4-6 mm Hg.

7. Mixed venous gas composition

blood: Pv02 within 34-40 mm Hg, Sv02 - 70-77%. A decrease in these indicators indicates an increase in oxygen extraction by tissues, which indirectly indicates a deterioration in hemodynamics and organ perfusion. On the other hand, an increase in these indicators indicates shunting of arterial blood into tissues and tissue hypoxia.

8. Volume-pressure loop (see Chapter 8; p. 204). The "optimal" PEEP should approach the lung opening pressure point.

Indications

and contraindications to PEEP

Indications for use of PEEP:

1. Moderate PEEP(4-5 cm water column) is indicated for all patients who undergo mechanical ventilation, even with

in the absence of obvious lung pathology. This PEEP level is considered “physiological”, since during normal spontaneous breathing at the end of expiration, the closure of the glottis creates a PEEP of the order of 2-3 cm of water column. “Physiological” PEEP helps prevent atelectasis, better distribute the supplied gas across the lung fields and reduce airway resistance.

2. The main indication for higher PEEP numbers (> 7 cm water column, if necessary - up to 10-15 cm water column) is a restrictive pathology of the lungs, especially accompanied by atelectasis and collapse of the alveoli with intrapulmonary venous shunting blood - ARDS (ARDS), bilateral polysegmental pneumonia. Continued decrease in SaO and PaO against the background of high Fi02 (> 60%), as well as the Pa02 /Fi02 ratio< 250 являют­ ся абсолютным показанием к увели­ чению PEEP для предупреждения экспираторного коллабирования аль­ веол.

3 . Ventilation for pulmonary edema: PEEP promotes the retention of extravascular water in the interstitial space of the lungs. This requires particularly careful hemodynamic monitoring and titration of inotropic drugs is often indicated (for example, dopamine at a rate of 4-8 mcg/kg/min). Recommended PEEP for pulmonary edema - 6-8 cm water column

4 . Mechanical ventilation in patients with exacerbation of chronic obstructive pulmonary pathology. PEEP level 5-6 cm water column allows you to reduce resistance and reduce early expiratory closure of small airways, overcome the undesirable effects of autoPEEP, increase the effectiveness of bronchodilator therapy (in patients with bronchial asthma and COPD),

80 Part II. The main modern modes of international international flights

reduce the work of spontaneous breathing of the patient and improve synchronization with the ventilator^.

5. Assisted ventilation during the process of “weaning” from mechanical ventilation. PEEP at 4-5 cm water column. stored until extubation (or disconnection of the device from the tracheostomy tube). The use of PEEP allows for better synchronization of the patient with the ventilator, reduces the work of breathing to overcome the resistance of the endotracheal (tracheostomy) tube and prevents secondary atelectasis.

Relative contraindications

to PEEP (> 5 cm H 2 0):

unilateral or local severe lung damage;

high Pmean (> 18-19 cm water column);

recurrent pneumothorax;

severe hypovolemia and arterial hypotension (systolic blood pressure< 90 мм рт.ст.);

high ICP, cerebral edema;

PE (PEEP > 4-5 cm H2O may further increase resistance in the pulmonary artery basin).

PCV - ventilation

with controlled pressure (Pressure Control Ventilation)

Over the past 10-15 years, especially since the second half of the 90s, pressure-controlled ventilation has become one of the most widely used mechanical ventilation modes in patients with severe pulmonary pathology, as well as in pediatric practice (6, 13, 21 ). At present, it is impossible to imagine effective treatment of patients with severe restrictive lung pathology without PCV, especially patients with ALI and ARDS (ARDS). As a matter of fact, it was with the development

new mechanisms for the treatment of ARDS and the history of the creation of the PCV regimen began (34, 42). Traditional modes of ventilation with volume control could not provide satisfactory ventilation, because any restrictive lung pathology (especially ARDS) is characterized by a “mosaic pattern” of atelectasis associated with inhomogeneous damage and collapse of the alveoli.

As already described above (see volume-controlled ventilation), when a forced tidal volume is applied, it predominantly enters the more compliant areas of the lungs, these areas become overinflated, and the more affected areas remain collapsed. The developing high peak pressure in the airways causes severe barotrauma to relatively healthy areas of the lung tissue, and also contributes to the activation of inflammatory mediators released from the lung parenchyma, which support ARDS (74, 96, 48). High PEEP during volumetric ventilation does not solve the problem, since it further increases the peak pressure and negatively affects hemodynamics due to an increase in Pmean and intrathoracic pressure. As a result of an excessive increase in peak and average pressure in the respiratory tract, compression of the capillaries becomes possible, which aggravates ventilation-perfusion disorders.

That is why it was quite logical to propose regulating not the volume, but the pressure in ARDS. By the late 1980s, it became clear that pressure-controlled ventilation with controlled inspiratory timing could minimize the risk of barotrauma and significantly improve oxygenation in severe restrictive lung disease (166, 167). Since the beginning of the 90s, PCV mode has become an integral part of fans of all major world manufacturers.

Chapter 4. Forced ventilation 81

breathing equipment drivers (Siemens, Drager, Hamilton Medical, Mallinckrodt-NPB, Bird, Newport Medical, etc.).

The essence of the PCV mode is the controlled provision and maintenance of a given inspiratory (peak) pressure in the airways during the entire specified inhalation time (Fig. 4.19, a). In most modern 4th generation ventilators in PCV mode, the level of controlled pressure Pcontrol is set “above PEEP”, i.e. the total controlled inspiratory (peak) pressure Pinsp (Ppeak) is equal to the sum of Pcontrol and PEEP (Pinsp = Pcontrol + PEEP) . In previous generation respirators, Pinsp (aka Ppeak) was installed directly regardless of PEEP. This circumstance should be taken into account when setting PCV mode parameters on various devices. In practice, the actual level of controlled pressure is assessed using Ppeak monitoring data on the device. It is important to note that the pressure-controlled mode is time-cycled.

menu (Pressure Control Time-Cycled Ventilation): mechanical inspiration begins after a certain period of time (which depends on the set respiratory rate) and ends after the specified inhalation time. Direct adjustment of the inspiratory time Ti, during which controlled inspiratory pressure is maintained, is a characteristic feature of PCV.

Immediately after the start of inhalation, the device creates a sufficiently powerful flow to quickly achieve the set pressure level in the circuit. As soon as the pressure: ; flow in the circuit reaches the set level, the flow automatically decreases and the inhalation valve closes (point B1, Fig. 4.19, b). The powerful forced flow from the apparatus cannot instantly move from the circuit to the bronchioles and alveoli. Thus, at the very beginning of inspiration in PCV mode, a rather significant gradient is created between the pressure in the breathing circuit and large bronchi, on the one hand, and intrapulmonary (intra-alveolar) pressure, on the other. The result of such a gradient is

82 Part II. The main modern modes of international international flights

flow directed from the large bronchi into the small airways (bronchioles) and alveoli. The level of this flow is maximum at the beginning of inspiration, when there is still a significant pressure gradient between the trachea and bronchioles. Gradually, due to an increase in intrapulmonary pressure, the pressure gradient between the circuit and the lungs decreases, and therefore the respiratory flow

I of body gas also decreases (segment B1 -C, Fig. 4.19, b). The shape of the inspiratory flow curve turns out to be descending, which is one of the characteristic features of the PCV mode. As soon as the pressure in the large and small airways is equalized, the flow stops (point C, Fig. 4.19, b). If the time of forced inspiration has not yet ended, the zero flow phase begins (segment C1 - D1, Fig. 4.19, b), during this period the supplied air-oxygen mixture continues to participate in distribution over the distal pulmonary fields and gas exchange. In this case, the expiratory valve remains closed and the inspiratory pressure is maintained at the set level until the end of the inhalation time.

During the entire inhalation time, the device maintains and controls the set pressure level due to the coordinated closure of the inhalation and exhalation valves. Unlike volumetric ventilation, with PCV the pressure in the breathing apparatus is

in certain ways during inspiration does not increase, since upon reaching a given pressure the forced flow immediately stops and then has a spontaneous descending character. After the end of the forced inhalation time, the expiratory valve opens and passive exhalation begins (segments C-D and D"-E1, Fig. 4.19, a and b) to the level of the set external PEEP.

The physician can select any level of inspiratory pressure on the device, which the device will strictly control during the entire specified inspiratory time. Thus, tight control of inspiratory (peak) pressure during mandatory inspiration is the most characteristic feature of the PCV mode (42, 43).

The higher the peak inspiratory flow is set, the faster the working inspiratory pressure Pinsp will be achieved, i.e., according to modern terminology, the rate of increase in pressure Pramp will be greater (other names are Rise Time, Flow Acceleration). Pramp is the time during which 66% (in some respirator models - 95%) of Pcontrol is achieved. It is determined by the magnitude of the peak inspiratory flow (Fig. 4.20).

A number of modern fans allow you to directly adjust the Pramp value, while adjusting

Chapter 4. Forced ventilation 83

The flow changes automatically. The value of Pgatr is of greatest importance when performing controlled assisted or fully auxiliary ventilation (see description of the P-SIMV and PSV modes); it is used for adequate synchronization of the device with the patient.

As can be seen from Figure 4.20, in the PCV controlled ventilation mode, the Pgatr indicator affects the time at which the set pressure is maintained and, accordingly, the average pressure in the airways Pmean. At a low rate of pressure rise (Pgatr > 150 ms), Pteap may decrease to such a level that oxygenation will suffer. At a high rate of pressure rise (Pgatr 25 - 75 ms), Pteap will increase significantly; in some patients (especially with high PEEP) this may adversely affect hemodynamics. In general, when using PCV mode, it is recommended to maintain the rate of pressure rise as high as possible so that the pressure curve on the graph is closer to a rectangle (rectangular trapezoid) (b), and not to a flat trapezoidal shape (a). On the other hand, a rapid increase in pressure should be avoided in patients with unresolved hypovolemia and persistent arterial hypotension.

Modern fans allow for synchronized (assisted) ventilation with controlled

controlled pressure. If the patient still has spontaneous breathing attempts and the trigger is configured optimally, the set PCV parameters (Pcontrol, Pramp, Ti) will be synchronized with each inhalation attempt (Fig. 4.21, a), and the total respiratory rate may be higher than the set one . If such attempts are rare, very weak or stop, the number of PCV breaths will correspond to the set frequency of forced breaths (Fig. 4.21, b).

One of the clear advantages of the PCV mode is the ability to provide a lung protection strategy and improve ventilation in the most affected areas. Stable pressure is maintained at a given, predictable level, the likelihood of barotrauma is significantly reduced and it is possible to maintain Ppeak within safe limits. It is believed that the combination of a stable inspiratory pressure throughout the entire inspiratory time and a descending inspiratory flow provides the most optimal conditions for uniform ventilation of different zones of the lungs, affected to a greater and lesser extent (13, 43, 45, 116).

It has already been shown in a two-component lung model that volumetric ventilation preferentially ventilates and overinflates “healthy” areas of the lungs (74, 96, 123, 148). Peak pressure is unpredictable and is significantly higher in “healthy” areas (P) than in

84 Part II. The main modern modes of the Ministry of Internal Affairs

affected (P2) (Fig. 4.22, a). If these zones are adjacent to each other, then due to the pressure gradient, so-called “tearing” forces appear, causing barotrauma of the lung tissue. At high pressure, conditions are created for damage to the bronchiolar and alveolar epithelium, the release of inflammatory mediators is stimulated, the mechanisms of ALI (ARDS) are triggered and maintained, and the pathological process in the lungs is aggravated. Compression of the capillaries causes disruption of pulmonary blood flow in relatively “healthy” areas of the lungs. The pressure in the affected areas (P2) remains relatively low, insufficient to open the collapsed alveoli, and the pathological areas of the lungs remain collapsed. The result is atelectasis, impaired gas exchange and worsening shunting of unoxygenated blood from right to left, progression of hypoxemia and hypoxic hypoxia.

A significantly more favorable situation with the distribution of ventilation, according to modern concepts, occurs with mechanical ventilation in PCV mode (Fig. 4.22, b). As already noted, tightly controlled airway pressure

together with the descending inspiratory flow, they lead to an approximate equalization of pressures in different zones of the lungs - “healthy” (P,) and “sick” (P2), P, ~ P2. The affected areas of the alveoli experience powerful, controlled pressure throughout inhalation, which forces the collapsed alveoli to open and ventilate (at least some of them). If P, ~ P2, then the pressure gradient between the “sick” and “healthy” zones is relatively small, if “tearing” forces appear, they are small, and the pathological mechanisms of ALI and/or ARDS do not progress. The involvement of a larger number of alveoli in the ventilation process and the stability of alveolar opening in PCV mode certainly contribute to:

improving compliance (extensibility) of lung tissue (volume increases at the same pressure);

reducing the degree of shunting of unoxygenated blood;

improvement of oxygenation without the use of high oxygen concentrations (Fi0 2 < 60 %).

In addition, with PCV, due to controlled inspiratory pressure, the gradient between Pcontrol and PEEP can (and

necessary!) be maintained relatively small, which is important for reducing the risk of barotrauma. The small difference between inspiratory pressure and PEEP contributes to a decrease in transpulmonary pressure and amplitude of lung motion, which creates relative “rest of the affected organ - the lungs” (13, 151). Many authors note an improvement in oxygenation during mechanical ventilation in the PCV mode in patients with restrictive pathology (ARDS, the Pa02 / Fi02 ratio remains more than 200), a decrease in intrapulmonary shunting while maintaining a relatively low peak pressure and tidal volume (13, 20, 31, 34 , 39, 43, 82, 123). This indicates a significant improvement in gas distribution in the lungs with this mode of ventilation.

PCVM "open lung" concept

In addition to the strategy of protecting the lungs from barotrauma, the PCV mode allows the greatest support for the concept of “open lungs” (OL). The essence of the OL concept developed

IN. Lachman et al. (121, 122), consists

V that it is necessary to achieve the opening of the collapsed affected areas of the lungs (alveoli) and maintain them in an open state during all phases of breathing (inhalation and exhalation), preventing collapse. There is no need to explain that constantly maintaining the small airways and alveoli in an open state increases FRC volume, improves gas exchange and oxygenation without the use of high concentrations of oxygen. It is on the basis of the concept of OL that modern tactics of mechanical ventilation for ARDS (ARDS) are built. In this case, it is very important not only to open the bronchioles and alveoli, but also to maintain them in this state, preventing repeated collapse. Alternation of collapsing alveoli (on exhalation) with their forced

rapid opening during inspiration is unacceptable: this requires significantly greater inspiratory pressure (risk of barotrauma) and, in addition, the process of inactivation and removal of surfactant is intensified and the “tearing” forces between the alveoli are intensified.

The OL concept is based on a deep understanding of the physiology of the lungs and the influence of various modes of mechanical ventilation on lung tissue. As is known from physiology and biophysics, pulmonary surfactant, a phospholipid substance produced by type II pneumocytes, plays a huge role in maintaining the alveoli in an expanded state. Surfactant reduces the surface tension of the alveolar wall, preventing them from collapsing during exhalation. It also promotes uniform alignment of alveoli of different sizes during inhalation.

According to Laplace's law,

where P is the pressure in the alveoli, T is the surface tension of the alveoli, R is the radius of the alveoli.

According to the formula, the smaller the size of the alveoli, the greater the pressure required to expand them. However, this does not normally happen: the concentration of surfactant is higher in the alveoli of small radius, the surface tension in them decreases to a greater extent and they are more pliable than alveoli with a large radius. As a result, during inhalation at the same pressure, alveoli with different radii expand to the same extent.

In severe lung pathology (especially restrictive, inhomogeneous), the production and destruction of surfactant is disrupted, its concentration in the affected areas of the lungs decreases, the surface tension of the alveoli increases, and their radius decreases. During exhalation, a significant part of the alveoli collapses and the FRC volume of the lungs

86 Part II. Basic modern Ministry of Internal Affairs regimes

decreases significantly. As follows from Laplace's law, the expansion of collapsed alveoli (with a small radius) requires significantly greater inspiratory pressure than for open alveoli (with a large radius). Ventilation with volume control does not contribute to more or less adequate opening of the collapsed areas of the lungs, and the main part of the forced volume goes into the “healthy” part of the lungs, causing them to overstretch and the appearance of “bursting” forces between the collapsed and inflated acini, barotrauma, “washing out” surfactant, etc. Consequently, for the straightening of pathological zones of the lungs, ventilation with controlled pressure is physiologically justified, providing theoretically and practically more uniform gas distribution with maintaining and balancing pressure in different parts of the lungs.

As a rule (but not always justified!), ventilation in the PCV mode is resorted to after volumetric ventilation has been used for some time and the progression of pulmonary pathology and a drop in oxygenation have already taken place. Based on this kind of observations, the author recommends, if time and appropriate breathing equipment are available, to use the PCV regimen in patients at risk of severe

pulmonary pathology as early as possible, without waiting for severe disturbances in pulmonary mechanics and oxygenation.

Application of the open lung concept

With severe restrictive lung disease, the total surface area of ​​the lungs involved in gas exchange is significantly reduced. This is mainly due to the collapse of a significant part of the alveoli, which remain collapsed not only during exhalation, but also during inhalation. According to the “Open Lung” concept, in such cases the main goal of mechanical ventilation is to “open” the alveoli and maintain them and the small airways in an open state throughout the entire respiratory cycle. In reality, this can be achieved using the PCV mode and/or its analogues (PSIMV, BIPAP).

For the initial opening of collapsed areas of the lungs, it is necessary to achieve a certain level of “opening of the alveoli” pressure. This is the level of controlled inspiratory pressure at which the force of surface tension of the collapsed alveoli is overcome, they begin to ventilate and take part in gas exchange. Of course, we are talking about those alveoli that are potentially still

Chapter 4. Forced ventilation 87

capable of straightening out. An adequate level of PEEP is required to prevent subsequent alveolar collapse during expiration.

Figure 4.23 shows that the inspiratory volume begins to flow into the restrictive zones of the lungs only after achieving sufficient alveolar opening pressure Po. Once the alveoli are open, their subsequent ventilation requires a lower inspiratory pressure (Pv), which must be kept in mind when setting Pcontrol. Thus, Pv is the minimum inspiratory pressure that allows ventilating the collapsed parts of the lungs after they open (with the help of Po). The controlled pressure should not be below the Pv level, otherwise the affected (but potentially ventilated) alveoli will not inflate during inspiration. In this regard, it is necessary to change the controlled pressure quite often in order to ultimately achieve its optimal and least possible level for sufficient ventilation.

In practice, when transferring mechanical ventilation to PCV mode, the inhalation to exhalation ratio is set to 1: 1.5 - 1: 1 (Ti = 1.5-2.5 s) and then they begin to select the required inspiratory pressure and PEEP. The oxygen concentration Fi02 is set at the level

50-55% (if necessary, in order to correct existing severe hypoxia, initially its level may be higher - up to 60-70%).

If the patient has previously been ventilated with volume control, the initial level of Pcontrol in PCV mode is set equal to the previous inspiratory pause pressure (Pplat) (Fig. 4.24). If mechanical ventilation immediately begins with PCV, then the initial Pcontrol is set at 18-20 cm water column, the initial PEEP values ​​are 6-7 cm water column.

As already noted, PCV is indicated for patients with ARF of pulmonary parenchymal origin (bilateral polysegmental pneumonia, ARDS, atelectasis, etc.), when there is a significant decrease in the compliance of the lung tissue (Cst< 35 мл/см вод.ст.) и нарушение оксигенации.

After starting ventilation in PCV mode with the above set parameters Pcontrol, PEEP and I: E, the initial values ​​of Vle, pulse oximetry (Sa02), BP, heart rate and blood gases (primarily Pa02 and PaCO2) are noted. If the lung pathology has not yet led to a serious gas exchange disorder, these indicators may be within normal limits (Sa02 > 94%, Pa02 > 65 mm Hg). In such a situation, it would be a mistake to return to the regime with con-

End-expiratory pressure(PEEP) increases as the accumulated volume of gas in the alveoli increases. Since in this case there are no real conditions that prevent the movement of expiratory volume along the respiratory tract (open valveless system, extremely low volume of hardware dead space), it is logical to assume that the increase in end-expiratory pressure is carried out due to an increase in alveolar pressure, which is formed on exhalation before the beginning of the next inhalation.

His magnitude is associated only with the volume of gas remaining in the alveoli, which, in turn, depends on the distensibility of the lungs and the aerodynamic resistance of the airways, which is called the “lung time constant” (the product of distensibility and airway resistance) and affects the time of filling and emptying of the alveoli . Therefore, in contrast to PEEP (positive end expiratory pressure), positive alveolar pressure, being “internal” and relatively independent of external conditions, is called auto-PEEP in the literature

This thesis finds confirmation when analyzing the dynamics of these parameters at different VFS frequencies. The figure shows the results of recording PEEP and auto-PEEP at increasing ventilation frequencies under conditions of approximately the same tidal volume and ratio I: E = 1: 2.
As increasing ventilation frequency There is a steady increase in both parameters (diagram A). Moreover, the specific gravity of auto-PEEP in the final expiratory pressure is 60-65%.

By the amount of auto-PEEP, in addition to the frequency of ventilation, the duration of the phases of the respiratory cycle I:E also influences.
Auto-PEEP frequency level is directly dependent on the frequency of ventilation and the duration of the expiratory phase of the respiratory cycle.

The above data allows state that during high-frequency ventilation, end-expiratory pressure (PEEP) is closely related to auto-PEEP and, like auto-PEEP, depends on the duration of exhalation and the volume of the gas mixture remaining in the alveoli after its cessation. This circumstance allows us to conclude that during high-frequency ventilation the basis of the final expiratory pressure is alveolar pressure.
This conclusion confirmed the results of a correlation analysis of the mutual influence of PEEP and auto-PEEP with other parameters of respiratory mechanics.

Auto-PEEP correlation links with other parameters of breathing mechanics is closer than that of PEEP. This is especially clearly evident when comparing the correlation coefficients of tidal volume (VT), which is another confirmation of the previously established nature and pattern of occurrence of auto-PEEP.

The above facts allow approve that in the absence of severe airway obstruction, end-expiratory pressure, determined by modern jet respirators, is nothing more than alveolar pressure (auto-PEEP), but recorded not at the level of the alveoli, but in the proximal parts of the respiratory circuit. Therefore, the values ​​of these pressures differ significantly. According to our data, the auto-PEEP level can exceed the PEEP value by one and a half times or more.
Hence, according to PEEP level it is impossible to obtain correct information about the state of alveolar pressure and the degree of hyperinflation. To do this, you must have information about auto-PEEP.