High-frequency oscillatory ventilation in experimental lung injury: effects on gas exchange.

Objective: To compare ventilation-perfusion (V(A)/Q) distributions during improvement of oxygenation caused by high-frequency oscillatory ventilation (HFOV) and pressure-controlled mechanical ventilation with high PEEP levels (CMV) in experimental acute lung injury (ALI).
Design: Prospective, controlled animal study.
Setting: Animal research facility of a university hospital.
Interventions: Twelve pigs with oleic acid-induced ALI were randomised to HFOV ( n=6) or to CMV ( n=6) with a PEEP of 15 mbar for 1 h. The mean airway pressure was adjusted in both groups to achieve comparable improvements in arterial oxygen partial pressure (PaO(2)) and to avoid clinically relevant impairments of cardiac output, as assured by adequate mixed venous oxygen saturation and lactate levels. V(A)/Q distributions were determined by the multiple inert gas elimination technique (MIGET).
Measurements and Results: Arterial oxygen partial pressure improved during CMV with a mean airway pressure of 20 mbar ( p<0.05) whereas HFOV revealed comparable improvements with a mean airway pressure of 40 mbar ( p<0.05). Shunt decreased and blood flow to normal V(A)/Q areas increased due to CMV and HFOV ( p<0.05). The perfusion of low V(A)/Q areas remained unchanged. Statistical analysis did not reveal differences of PaO(2), shunt or blood flow to low V(A)/Q areas between the groups.
Conclusions: In this model of acute lung injury CMV and HFOV improved gas exchange due to similar changes in V(A)/Q distribution. However, mean airway pressure had to be adjusted twofold higher during HFOV then during CMV to achieve comparable improvements in gas exchange.