BAROTRAUMA AND MICROVASCULAR INJURY IN LUNGS OF NONADULT RABBITS - EFFECT OF VENTILATION PATTERN

To study the pulmonary microvascular injury produced by ventilation barotrauma, the isolated perfused lungs of 4 to 6-wk-old New Zealand white rabbits were ventilated by one of the following methods: peak inspiratory pressure (PIP) 23 cm H2O, gas flow rate 1.1 L/min (group 1); PIP 27 cm H2O, gas flow rate 6.9 L/min (group 2); PIP 50 cm H2O, gas flow rate 1.9 L/min (group 3); or PIP 53 cm H2O, gas flow rate 8.3 L/min (group 4). Microvascular permeability was assessed using the capillary filtration coefficient (K(fc)) before and 5, 30, and 60 min after a 15-min period of ventilation. Baseline K(fc) was not significantly different between groups. A significant increase over the baseline K(fc) was noted at 60 min in group 2 and in all postventilation K(fc) values in groups 3 and 4 (p < .05). Group 1 K(fc) values did not change significantly after ventilation. At all postventilation times, values for K(fc) were significantly greater in groups 3 and 4 than in group 1 (p < .05). Group 4 K(fc) values were significantly greater than those in group 2 at 5 and 30 min postventilation. These data indicate that high PIP, and to a lesser extent, high gas flow rates cause microvascular injury in the compliant nonadult lung and suggest that the combination of high PIP and high gas flow rates are the most threatening to microvascular integrity.