Effects of sustained inflation and postinflation positive end-expiratory pressure in acute respiratory distress syndrome: Focusing on pulmonary and extrapulmonary forms

OBJECTIVETo investigate whether the response to sustained inflation and postinflation positive end-expiratory pressure varies between acute respiratory distress syndrome with pulmonary (ARDSp) and extrapulmonary origin (ARDSexp). DESIGNProspective clinical study. SETTINGMultidisciplinary intensive care unit in a university hospital. PATIENTSA total of 11 patients with ARDSp and 13 patients with ARDSexp. INTERVENTIONSA 7 ml/kg tidal volume, 12–15 breaths/min respiratory rate, and an inspiratory/expiratory ratio of 1:2 was used during baseline ventilation. Positive end-expiratory pressure levels were set according to the decision of the primary physician. Sustained inflation was performed by 45 cm H2O continuous positive airway pressure for 30 secs. Postinflation positive end-expiratory pressure was titrated decrementally, starting from a level of 20 cm H2O to keep the peripheral oxygen saturation between 92% and 95%. Fio2 was decreased, and baseline tidal volume, respiratory rate, inspiratory/expiratory ratio were maintained unchanged throughout the study period. MEASUREMENTS AND MAIN RESULTSBlood gas, airway pressure, and hemodynamic measurements were performed at the following time pointsat baseline and at 15 mins, 1 hr, 4 hrs, and 6 hrs after sustained inflation. After sustained inflation, the Pao2/Fio2 ratio improved in all of the patients both in ARDSp and ARDSexp. However, the Pao2/Fio2 ratio increased to >200 in four ARDSp patients (36%) and in seven ARDSexp patients (54%). In two of those ARDSp patients, the Pao2/Fio2 ratio was found to be