Effects of recruiting maneuvers in patients with acute respiratory distress syndrome ventilated with protective ventilatory strategy

Abstract

Background: A lung-protective ventilatory strategy with low tidal volume (V T) has been proposed for use in acute respiratory distress syndrome (ARDS). Alveolar derecruitment may occur during the use of a lung-protective ventilatory strategy and may be prevented by recruiting maneuvers. This study examined the hypothesis that the effectiveness of a recruiting maneuver to improve oxygenation in patients with ARDS would be influenced by the elastic properties of the lung and chest wall. Methods: Twenty-two patients with ARDS were studied during use of the ARDSNet lung-protective ventilatory strategy: V T was set at 6 ml/kg predicted body weight and positive end-expiratory pressure (PEEP) and inspiratory oxygen fraction (FIO 2 were set to obtain an arterial oxygen saturation of 90-95% and/or an arterial oxygen partial pressure (Pao 2) of 60-80 mmHg (baseline). Measurements of Pao 2/FIO 2, static volume-pressure curve, recruited volume (vertical shift of the volume-pressure curve), and chest wall and lung elastance (Est w and Est L: esophageal pressure) were obtained on zero end-expiratory pressure, at baseline, and at 2 and 20 min after application of a recruiting maneuver (40 cm H 2O of continuous positive airway pressure for 40 s). Cardiac output (transesophageal Doppler) and mean arterial pressure were measured immediately before, during, and immediately after the recruiting maneuver. Patients were classified a priori as responders and nonresponders on the basis of the occurrence or nonoccurrence of a 50% increase in Pao 2/FIO 2 after the recruiting maneuver. Results: Recruiting maneuvers increased Pao 2/FIO 2 by 20 ± 3% in nonresponders (n = 11) and by 175 ± 23% (n = 11; mean ± standard deviation) in responders. On zero end-expiratory pressure, Est L (28.4 ± 2.2 vs. 24.2 ± 2.9 cm H 2O/I) and Est w (10.4 ± 1.8 vs. 5.6 ± 0.8 cm H 2O/I) were higher in nonresponders than in responders (P < 0.01). Nonresponders had been ventilated for a longer period of time than responders (7 ± 1 vs. 1 ± 0.3 days; P < 0.001). Cardiac output and mean arterial pressure decreased by 31 ± 2 and 19 ± 3% in nonresponders and by 2 ± 1 and 2 ± 1% in responders (P < 0.01). Conclusions: Application of recruiting maneuvers improves oxygenation only in patients with early ARDS who do not have impairment of chest wall mechanics and with a large potential for recruitment, as indicated by low values of Est L.