Mean Airway Pressure

Background: Hypoxemia in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) patients represents a common finding in the intensive care unit (ICU) and frequently does not respond to standard ventilatory techniques. Objective: To study whether the early short-term application of high-frequency percussive ventilation (HFPV) can improve gas exchange in hypoxemic patients with ALI/ARDS or many other conditions in comparison to conventional ventilation (CV) using the same mean airway pressure (Paw), representing the main determinant of oxygenation and hemodynamics, irrespective of the mode of ventilation. Methods: Thirty-five patients not responding to CV were studied. During the first 12 h after admission to the ICU the patients underwent CV. Thereafter HFPV was applied for 12 h with Paw kept constant. They were then returned to CV. Gas exchange was measured at: 12 h after admission, every 4 h during the HFPV trial, 1 h after the end of HFPV, and 12 h after HFPV. Thirty-five matched patients ventilated with CV served as the control group (CTRL). Results: PaO2/FiO2 and the arterial alveolar ratio (a/A PO2) increased during HFPV treatment and a PaO2/FiO2 steady state was reached during the last 12 h of CV, whereas both did not change in CTRL. PaCO2 decreased during the first 4 h of HFPV, but thereafter it remained unaltered; PaCO2 did not vary in CTRL. Respiratory system compliance increased after HFPV. Conclusions: HFPV improved gas exchange in patients who did not respond to conventional treatment. This improvement remained unaltered until 12 h after the end of HFPV.