High frequency oscillatory ventilation and prone positioning in a porcine model of lavage-induced acute lung injury.

Background: This animal study was conducted to assess the combined effects of high frequency oscillatory ventilation (HFOV) and prone positioning on pulmonary gas exchange and hemodynamics.

Methods: Saline lung lavage was performed in 14 healthy pigs (54 +/- 3.1 kg, mean +/- SD) until the arterial oxygen partial pressure (PaO2) decreased to 55 +/- 7 mmHg. The animals were ventilated in the pressure controlled mode (PCV) with a positive endexpiratory pressure (PEEP) of 5 cmH2O and a tidal volume (VT) of 6 ml/kg body weight. After a stabilisation period of 60 minutes, the animals were randomly assigned to 2 groups. Group 1: HFOV in supine position; group 2: HFOV in prone position. After evaluation of prone positioning in group 2, the mean airway pressure (Pmean) was increased by 3 cmH2O from 16 to 34 cmH2O every 20 minutes in both groups accompanied by measurements of respiratory and hemodynamic variables. Finally all animals were ventilated supine with PCV, PEEP = 5 cm H2O, VT = 6 ml/kg.

Results: Combination of HFOV with prone positioning improves oxygenation and results in normalisation of cardiac output and considerable reduction of pulmonary shunt fraction at a significant (p < 0.05) lower Pmean than HFOV and supine positioning.

Conclusions: If ventilator induced lung injury is ameliorated by a lower Pmean, a combined treatment approach using HFOV and prone positioning might result in further lung protection.