Objective: To compare the inspiratory volume pressure (VP) curves of the respiratory system (rs) produced by static occlusion (OCC) and dynamic low constant flow inflation (LCFI) methods using a new device in acute respiratory distress syndrome (ARDS) patients.
Setting: A multidisciplinary 24-bed ICU in a tertiary university hospital.
Patients: Eleven intubated and mechanically ventilated patients with ARDS.
Measurements and results: OCC and LCFI methods were performed using the same ventilator, which had been specifically implemented for this purpose. LCFI of 5, 10, and 15 l/min and OCC were applied in a random order at zero end-expiratory positive pressure. Airway pressure was measured both proximal (P(ao)) and distal (P(tr)) to the endotracheal tube. Lower inflection point (LIP) and maximal slope (C(max,rs)) were estimated using unbiased iterative linear regressions. LIP(rs) was obtained in all patients under LCFI and in nine patients under OCC. With LCFI of 5, 10, 15 l/min and OCC the average LIP(rs) values were 12.2 +/- 3.9, 12.9 +/- 4, 14.3 +/- 3.4, and 11.9 cm H(2)O for P(ao) and 11.9 +/- 3.9, 11.5 +/- 3.3, 12.5 +/- 3.4 and 11.8 +/- 4.4 for P(tr), respectively. Only the mean values of LIP(rs) for P(ao) with LCFI at 15 l/min were significantly different from those obtained for OCC. The C(max,rs) values found with the two methods were similar.
Conclusions: An LCFI less than or equal to 10 l/min seems to be a quick, safe, and reliable method to determine LIP(rs) and C(max,rs) at the bedside.