Effects of Peak Inspiratory Flow on Development of Ventilator-induced Lung Injury in Rabbits


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Abstract

Background:A lung-protecting strategy is essential when ventilating acute lung injury/acute respiratory distress syndrome patients. Current emphasis is on limiting inspiratory pressure and volume. This study was designed to investigate the effect of peak inspiratory flow on lung injury.Methods:Twenty-four rabbits were anesthetized, tracheostomized, ventilated with a Siemens Servo 300, and randomly assigned to three groups as follows: 1) the pressure regulated volume control group received pressure-regulated volume control mode with inspiratory time set at 20% of total cycle time, 2) the volume control with 20% inspiratory time group received volume-control mode with inspiratory time of 20% of total cycle time, and 3) the volume control with 50% inspiratory time group received volume-control mode with inspiratory time of 50% of total cycle time. Tidal volume was 30 ml/kg, respiratory rate was 20 breaths/min, and positive end-expiratory pressure was 0 cm H2O. After 6 h mechanical ventilation, the lungs were removed for histologic examination.Results:When mechanical ventilation started, peak inspiratory flow was 28.8 ± 1.4 l/min in the pressure regulated volume control group, 7.5 ± 0.5 l/min in the volume control with 20% inspiratory time group, and 2.6 ± 0.3 l/min in the volume control with 50% inspiratory time group. Plateau pressure did not differ significantly among the groups. Gradually during 6 h, Pao2 in the pressure regulated volume control group decreased from 688 ± 39 to a significantly lower 304 ± 199 mm Hg (P < 0.05) (mean ± SD). The static compliance of the respiratory system for the pressure regulated volume control group also ended significantly lower after 6 h (P < 0.05). Wet to dry ratio for the pressure regulated volume control group was larger than for other groups (P < 0.05). Macroscopically and histologically, the lungs of the pressure regulated volume control group showed more injury than the other groups.Conclusion:When an injurious tidal volume is delivered, the deterioration in gas exchange and respiratory mechanics, and lung injury appear to be marked at a high peak inspiratory flow.

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