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Correction methods for acute respiratory failure in acute lung injury / acute respiratory distress syndrome with a proven effect on mortality and ventilator-induced lung damage
• ???? Ventilation with small respiratory volumes. The use of small respiratory volumes allows to reduce the manifestations of volutrauma and to avoid high transpulmonary pressures. According to the largest multicenter randomized controlled study conducted by ARDSnet in 41 centers and involving 861 patients, the use of small respiratory volumes (6 ml / kg body weight) leads to a decrease in mortality in ALI / ARDS by 8.8% (a decrease in relative mortality of 22%) . This is the only study among analogues in which statistically significant differences were noted in the values of tidal volumes and plateau pressures among groups using confidence intervals. In addition, the number of randomized patients in this study significantly exceeds the amount of patients in other similar studies. The use of respiratory volumes of 6 ml / kg of body weight in patients with ALI / ARDS was recommended.
• ???? Application of optimal peep. Optimal Peep is one of the most important factors in protecting the lungs from ventilator-induced lung damage (atelectatic injury) and ensuring oxygenation of arterial blood by keeping the alveoli “open”. It has been empirically proven that the use of PEEP in ALI / ARDS is less than 10 cm aq. Art. leads to increased mortality. The values of the optimal peep with APL / ARDS are mostly in the range of 10-15 cm aq. Art.
• ???? The use of alveoli recruitment maneuvers. Alveolar recruitment maneuver is a therapeutic device aimed at unraveling partially collaborative (potentially recruited, "unstable") alveoli. According to multicenter randomized controlled studies using computed tomography, the recruitment of alveoli can significantly increase the number of functioning alveoli, increase the respiratory index and reduce the shunt fraction (“open” the lungs). Recruitment maneuvers are used in the early stage of ARDS (before fibroproliferation develops), and patients with extrapulmonary ARDS respond better to the maneuver than patients with primary lung disease. Recruitment maneuver can be performed both in the supine position and in the prone position (more effectively). Before the beginning of the maneuver, the patient is injected with a sedative and a muscle relaxant and an analysis of the arterial blood gas composition is carried out. The maneuver is carried out by creating a constantly positive pressure (CPAP, Pinsp) in 40 cm aq. Art. for 30-40 sec with the subsequent return to the established parameters of respiratory support and selection of optimal PDKV to prevent re-collapse of the alveoli, which composes the maneuver is monitored blood pressure, heart rate, SpO2. After the maneuver, arterial blood gas analysis is repeated. If there is no effect, the maneuver can be repeated. Given the possibility of “de-twisting” the alveoli, it is often necessary to reapply the maneuver after a few hours.
• ???? Protective ventilation of the lungs. The combination of small respiratory volumes, recruitment maneuvers of the alveoli and optimal peep due to the sparing effect on the lung parenchyma was called protective ventilation of the lungs. This methodology leads to a decrease in ventilator-induced lung damage in ALI / ARDS (barotrauma, volumetric trauma, atelectatic trauma and biotrauma), a decrease in transpulmonary pressure and plateau pressure, no increase in plasma cytokines and a decrease in mortality in ALA / ARDS.
• ???? Ventilation in the prone position. Ventilation of the lungs in the prone position leads to the involvement of non-functioning alveoli in the gas exchange (recruitment), an increase in the functional residual capacity of the lungs, an improvement in ventilation-perfusion ratios, a decrease in ventilator-induced lung damage and an improvement in lung drainage function. According to randomized multicenter studies, a significant decrease in mortality was found when applying ventilation in the prone position with an extremely severe course of respiratory distress syndrome, which was 24% in the subgroup with an initial respiratory index of less than 88 mm Hg. Art. and 30% in the subgroup with a baseline SAPS II score of more than 49 points. The use of this maneuver is recommended for all patients who do not have contraindications to the prone position (skeletal traction, laparotomy). For extremely severe distress syndrome a, extrapulmonary distress syndrome, the use of ventilation in the prone position is the method of choice.
Correction methods for acute respiratory failure in acute lung injury / acute respiratory distress syndrome with unproven effects on mortality
• ???? High-frequency ventilation of the lungs. According to the methodology, high-frequency ventilation of the lungs is a type of protective ventilation of the lungs, since ultralow respiratory volumes are used, high auto-PDKV is created, and there is practically no increase in cytokines in the blood plasma. However, there are no evidence-based studies on the use of HF ALV in patients with ALI / ARDS, therefore, the assessment of the efficacy and safety of HF ALV in ALI / ARDS is evaluated by doctors in each particular case. There are no recommendations on the use of the technique in patients with ALI / ARDS.
• ???? Ventilation with inverse ratio of inhalation to exhalation and permissible hypercapnia. Ventilation of the lungs with an inverse ratio of inhalation to exhalation leads to a reduction in the shunt and to improve the oxygenation of arterial blood in patients with ALI / ARDS, mainly due to the creation of high auto PDKV. In the studies, no differences were obtained when applying the optimal adjusting PEEP and the non-inverted inspiratory to expiratory ratio as compared to auto-PDKV and the inverse inspiratory to expiratory ratio. But the inverse ratio of inhalation to exhalation is less comfortable for the patient, requires deep sedation and myoplegia with the risk of complications arising in this case, and auto-PDKV inhibits hemodynamics to a greater degree than external PDKV. The permissible hypercapnia resulting from such ventilation modes may lead to adverse neurological consequences.
The positive effects of tolerable hypercapnia in mechanical ventilation have not been studied enough, although some authors believe that hypercapnia itself is a protective factor in ALI / ARDS, leading to a decrease in lung cytokine production. Considering hemodynamic depression and deterioration of ventilation / perfusion distribution during deep sedation, ventilation with an inverse inspiratory to expiratory ratio cannot be recommended as the treatment of choice for ALI / ARDS in severe sepsis. The question of the use of permissible hypercapnia should be decided individually. Indications for use of this technique should be strictly limited, if possible, reduce the time of hypercapnia, it is necessary to carefully monitor the neurological status and conduct deep medical sedation. The absolute contraindications are the acute period of severe TBI, decompensated brain disease with the development of brain edema (cerebral infarction, brain hemorrhage, brain tumor, episyndrome).
• ???? Inhalation use of nitric oxide (II). Randomized multicenter controlled studies on the use of inhaled nitric oxide (II) in patients with ALI / ARDS showed an improvement in oxygenation in all groups of patients and an improvement in survival in some groups of patients (inspiratory fraction of NO 5 ppm). However, in these studies, the number of patients in whom sepsis was the cause of lung damage was small. Inhalation therapy with nitric oxide (II) may be recommended as a reserve therapy in patients with ARDS.
• ???? Extracorporeal membrane oxygenation. In a number of uncontrolled studies, data were obtained on improving oxygenation and survival among patients with extremely severe acute respiratory distress syndrome (average Murray score of more than 3 points and an average respiratory index less than 70 mmHg). Controlled studies on the application of this technique were not conducted. Extracorporeal membrane oxygenation can be recommended as a reserve therapy in patients with extremely severe ARDS.
• ???? Non-invasive ventilation. It is possible to use non-invasive ventilation of the lungs in patients with ARDS under the following conditions: patient's clear consciousness, patient's cooperation with staff, absence of trauma to the facial skeleton, clinic for severe sepsis or PON.
Damage factors in mechanical ventilation: the factors of lung damage that have been proven to date (“aggression factors in mechanical ventilation”) are:
• ???? respiratory volume more than 10 ml / kg;
• ???? inspiratory fraction of oxygen more than 0.6;
• ???? inverted inhalation to exhalation ratio;
• ???? inadequate peep.
Criteria of adequacy of mechanical ventilation:
Criteria for the onset of respiratory support for ARDS:
• ???? absolute:
- lack of spontaneous breathing and abnormal respiratory rhythms;
- Violation of the upper respiratory tract;
- shock of any genesis;
- hemodynamic disorders (life-threatening arrhythmias, persistent tachycardia more than 120 per minute, hypotension);
• ???? relative (a combination of 2 or more factors is an indication for the onset of respiratory support):
- decrease in respiratory index less than 300 mm Hg. Art. when combined with other criteria;
- development of encephalopathy and swelling of the brain with depression of consciousness and impaired respiratory function;
- hypercapnia or severe hypocapnia;
- tachypnea more than 40 per minute (or 24 for exacerbation of chronic obstructive pulmonary disease) and a progressive increase in the minute volume of ventilation;
- reduction of VC less than 10 ml / kg body weight;
- progressive reduction of compliance;
- an increase in airway resistance of more than 15 cm aq. Art./l / sec;
- patient fatigue, involvement of auxiliary respiratory muscles.
Criteria for the beginning of the cancellation of respiratory support:
• ???? clear consciousness, the absence of neurological signs of swelling of the brain (for example, patients can be weaned in a vegetative state) and abnormal rhythms of respiration;
• ???? positive dynamics of infiltrates on a chest radiograph;
• ???? hemodynamic stability and the absence of life-threatening rhythm disturbances with the dopamine (dobutamine) dosing rate of less than 5 µg / kg / min, mezaton in any dosage;
• ???? increasing over time statistical compliance;
• ???? airway resistance less than 10 cm aq. Art./l / sec;
• ???? no violations of the acid-base state;
• ???? Tobin index (f / Vt) less than 105;
• ???? fever <38 ° C;
• ???? lack of pronounced manifestations of DIC (clinically significant bleeding or hypercoagulation).
In this case, a decrease in respiratory support is performed in stages, at each stage should be:
• ???? reduction of the inspiratory fraction of oxygen (initial FiO2 <0.4);
• ???? gradual reduction of hardware breaths to zero (if they were specified) with the installation of a support pressure equal to the pressure plateau of the hardware breath;
• ???? a gradual decrease in the level of inspiratory pressure under the control of the Tobin index (f / Vt should be less than 105) to 4 cm aq. Art. (in the presence of an endotracheal tube) or to zero (with a tracheostomy tube);
• ???? gradual decrease in PEEP / CPAP by 1–2 cm aq. Art. to zero level.
Transfer of the patient to fully independent breathing is possible when the minimum level of respiratory support is reached (FiO2 less than 0.3, PDKV less than 5 cm aq. Art., Inspiratory pressure less than 4 cm aq. Art. From the level of Peep, Tobin index less than 105) and the criteria adequacy of pulmonary ventilation.
The main causes of failures at weaning from a respirator:
• ???? continuing respiratory distress syndrome (for example, severe fibroproliferative stage of ARDS);
• ???? neurological causes (abnormal respiratory rhythms, polyneuropathy);
• ???? violation of the patient's food (depletion of protein and energy reserves);
• ???? atrophy of the respiratory muscles.
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