Increasing inspiratory time exacerbates ventilator-induced lung injury during high-pressure/high-volume mechanical ventilation

Introduction: Ventilator-induced lung injury may be caused by overdistension of alveoli during high-pressure ventilation. In this study, we examined the effects of increasing inspiratory time on ventilator-induced lung injury. Methods: Sprague-Dawley rats were divided into four different groups with ten animals per group. Each group was then ventilated for 30 mins with one of four ventilator strategies. All groups were ventilated with an FIO2 of 1.0 and a positive end-expiratory pressure of 0 cm H2O. Group LoP was the negative control group and was ventilated with low pressures (peak inspiratory pressure = 12 cm H2O, rate = 30, and inspiratory time = 0.5 secs). Groups iT = 0.5, iT = 1.0, and iT = 1.5 were the experimental groups and were ventilated with high pressures (peak inspiratory pressure = 45 cm H2O, rate = 10, and inspiratory times = 0.5 secs, iT = 1.0 sec, and iT = 1.5 secs, respectively). Outcome measures included lung compliance, PaO2/FIO2 ratio, wet/dry lung weight, and dry lung/body weight. Results: Final static lung compliance (p = .0002) and PaO2/FIO2 (p = .001) decreased as inspiratory time increased. Wet/dry lung weights (p < .0001) and dry lung/body weights (p < .0001) increased as inspiratory time increased. Light microscopy revealed evidence of intra-alveolar edema and hemorrhage in the iT 1.0 and iT = 1.5 animals but not the LoP and iT = 0.5 animals. Conclusion: Increasing inspiratory time during high-pressure/high-volume mechanical ventilation is associated with an increase in variables of lung injury.