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 ARDSpand 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%. Fio2was 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 points: at baseline and at 15 mins, 1 hr, 4 hrs, and 6 hrs after sustained inflation. After sustained inflation, the Pao2/Fio2ratio improved in all of the patients both in ARDSpand ARDSexp. However, the Pao2/Fio2ratio increased to >200 in four ARDSppatients (36%) and in seven ARDSexppatients (54%). In two of those ARDSppatients, the Pao2/Fio2ratio was found to be <200, whereas none of the ARDSexppatients revealed Pao2/Fio2ratios of <200 at the 6-hr measurement. Postinflation positive end-expiratory pressure levels were set at 16.7 ± 2.3 cm H2O in ARDSexpand 15.6 ± 2.5 cm H2O in ARDSp. The change in Pao2/Fio2ratios was found statistically significant in patients with ARDSexp(p= .0001) and with ARDSp(p= .008). Respiratory system compliance increased in ARDSexppatients (p= .02), whereas the change in ARDSpwas not statistically significant.ConclusionsSustained inflation followed by high levels of postinflation positive end-expiratory pressure provided an increase in respiratory system compliance in ARDSexp; however, arterial oxygenation improved in both ARDS forms.