High peak inspiratory flow can aggravate ventilator-induced lung injury in rabbits

The study investigated the effect of peak inspiratory flow in a rabbit acute lung injury model.

Twenty-five male rabbits were anesthetized and mechanically ventilated with high tidal volume (V(T)) until PaO2 dropped below 300 mmHg. Then the animals were randomly assigned to two groups: group V (n=10) receiving volume-control ventilation and group P (n=10) receiving pressure-regulated volume-control ventilation. Each animal was ventilated for 8 h at the following settings: V(T) 20 ml/kg, positive end-expiratory pressure 5 cmH2O, and respiratory rate 20 breaths/min with inspiratory-to-expiratory ratio of 1:4. Whether eleven hours of pressure-regulated volume-control ventilation at a V(T) of 20 ml/kg was harmful in rabbits with healthy lungs (control group, n=5) was also investigated.

Group P's peak inspiratory flow was significantly (p<0.05) higher than group V's. From 4 h after the establishment of acute lung injury to the end of the experiment, group V's PaO2 values were significantly higher than group P's. Wet-to-dry ratio and upper lobe tissue injury scores were higher in group P than in group V. Control animals showed neither apparent lung injury after 11 h of mechanical ventilation nor deterioration in gas exchange during the protocol.

Compared with volume-control ventilation with V(T) (20 ml/kg), pressure-regulated volume-control ventilation with the same V(T) worsened oxygenation, histological injury score in tipper lobes, and wet-to-dry ratio in rabbits with injured lungs. The evidence suggests that greater deterioration in gas exchange and lung injury is associated with high inspiratory flow.