Acute respiratory distress syndrome (ARDS) is characterized by the acute onset of pulmonary edema of non-cardiogenic origin, along with bilateral pulmonary infiltrates and reduction in respiratory system compliance. The hallmark of the syndrome is refractory hypoxemia. Despite its first description dates back in the late 1970s, a new definition has recently been proposed. However, the definition remains based on clinical characteristic. In the present review, the diagnostic workup and the pathophysiology of the syndrome will be presented. Therapeutic approaches to ARDS, including lung protective ventilation, prone positioning, neuromuscular blockade, inhaled vasodilators, corticosteroids and recruitment manoeuvres will be reviewed. We will underline how a holistic framework of respiratory and hemodynamic support should be provided to patients with ARDS, aiming to ensure adequate gas exchange by promoting lung recruitment while minimizing the risk of ventilator-induced lung injury. To do so, lung recruitability should be considered, as well as the avoidance of lung overstress by monitoring transpulmonary pressure or airway driving pressure. In the most severe cases, neuromuscular blockade, prone positioning, and extra-corporeal life support (alone or in combination) should be taken into account.
What is the power delivered by the ventilator and how do the mechanical properties of the lung and chest wall change during the different phases of thoracic surgery? • Findings: The mechanical power delivered by the ventilator increased during lateral position and with one-lung ventilation despite the reduction in tidal ventilation. Lung elastance was higher than expected. • Meaning: The power delivered by the ventilator is higher in lateral position than in the supine position irrespective of the reduction in the tidal volume and the mechanical characteristics of the dependent lung deteriorate during anesthesia.BACKGROUND: During thoracic surgery, patients are usually positioned in lateral decubitus and only the dependent lung ventilated. The ventilated lung is thus exposed to the weight of the contralateral hemithorax and restriction of the dependent chest wall. We hypothesized that mechanical power would increase during one-lung ventilation in the lateral position. METHODS: We performed a prospective, observational, single-center study from December 2016 to May 2017. Thirty consecutive patients undergoing general anesthesia with mechanical ventilation (mean age, 68 ± 11 years; body mass index, 25 ± 5 kg•m −2 ) for thoracic surgery were enrolled. Total and partitioned mechanical power, lung and chest wall elastance, and esophageal pressure were compared in supine and lateral position with double-and one-lung ventilation and with closed and open chest both before and after surgery. Mixed factorial ANOVA for repeated measurements was performed, with both step and the period before or after surgery as 2 within-subject factors, and left or right body position during surgery as a fixed, betweensubject factor. Appropriate interaction terms were included. RESULTS: The mechanical power was higher in lateral one-lung ventilation compared to both supine and lateral position double-lung ventilation (11.1 ± 3.0 vs 8.2 ± 2.7 vs 8.7 ± 2.6; mean difference, 2.9 J•minute −1 [95% CI, 1.4-4.4 J•minute −1 ] and 2.4 J•minute −1 [95% CI, 0.9-3.9 J•minute −1 ]; P < .001 and P = .002, respectively). Lung elastance was higher during lateral position one-lung ventilation compared to both lateral and supine double-lung ventilation (24.3 ± 8.7 vs 9.5 ± 3.8 vs 10.0 ± 3.8; mean difference, 14.7 cm H 2 O•L −1 [95% CI, 11.2-18.2 cm H 2 O•L −1 ] and 14.2 cm H 2 O•L −1 [95% CI, 10.8-17.7 cm H 2 O•L −1 ], respectively) and was higher compared to predicted values (20.1 ± 7.5 cm H 2 O•L −1 ). Chest wall elastance increased in lateral position double-lung ventilation compared to supine (11.1 ± 3.8 vs 6.6 ± 3.4; mean difference, 4.5 cm H 2 O•L −1 [95% CI, 2.6-6.3 cm H 2 O•L −1 ]) and was lower in lateral position one-lung ventilation with open chest than with a closed chest (3.5 ± 1.9 vs 7.1 ± 2.8; mean difference, 3.6 cm H 2 O•L −1 [95% CI, 2.4-4.8 cm H 2 O•L −1 ]). The end-expiratory esophageal pressure decreased moving from supine position to lateral position one-lung ventilation while increased with the opening of the chest wall. CONCLUSIONS: M...
Objectives: Hysteresis of the respiratory system pressure-volume curve is related to alveolar surface forces, lung stress relaxation, and tidal reexpansion/collapse. Hysteresis has been suggested as a means of assessing lung recruitment. The objective of this study was to determine the relationship between hysteresis, mechanical characteristics of the respiratory system, and lung recruitment assessed by a CT scan in mechanically ventilated acute respiratory distress syndrome patients. Design: Prospective observational study. Setting: General ICU of a university hospital. Patients: Twenty-five consecutive sedated and paralyzed patients with acute respiratory distress syndrome (age 64 ± 15 yr, body mass index 26 ± 6 kg/m2, Pao 2/Fio 2 147 ± 42, and positive end-expiratory pressure 9.3 ± 1.4 cm H2O) were enrolled. Interventions: A low-flow inflation and deflation pressure-volume curve (5–45 cm H2O) and a sustained inflation recruitment maneuver (45 cm H2O for 30 s) were performed. A lung CT scan was performed during breath-holding pressure at 5 cm H2O and during the recruitment maneuver at 45 cm H2O. Measurements and Main Results: Lung recruitment was computed as the difference in noninflated tissue and in gas volume measured at 5 and at 45 cm H2O. Hysteresis was calculated as the ratio of the area enclosed by the pressure-volume curve and expressed as the hysteresis ratio. Hysteresis was correlated with respiratory system compliance computed at 5 cm H2O and the lung gas volume entering the lung during inflation of the pressure-volume curve (R 2 = 0.749, p < 0.001 and R 2 = 0.851, p < 0.001). The hysteresis ratio was related to both lung tissue and gas recruitment (R 2 = 0.266, p = 0.008, R 2 = 0.357, p = 0.002, respectively). Receiver operating characteristic analysis showed that the optimal cutoff value to predict lung tissue recruitment for the hysteresis ratio was 28% (area under the receiver operating characteristic curve, 0.80; 95% CI, 0.62–0.98), with sensitivity and specificity of 0.75 and 0.77, respectively. Conclusions: Hysteresis of the respiratory system computed by low-flow pressure-volume curve is related to the anatomical lung characteristics and has an acceptable accuracy to predict lung recruitment.
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