Abstract

Background: The study investigated the effect of peak inspiratory flow in a rabbit acute lung injury model.
Material and methods: 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 cm H₂O, 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.
Results: Group P’s peak inspiratory flow was significantly (<i>p</i><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.
Conclusions: 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 upper 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.

Keywords: Lung - physiopathology, Analysis of Variance, Lung Injury, Positive-Pressure Respiration - adverse effects, Pressure, Rabbits, Respiratory Mechanics - physiology, Tidal Volume