Bronchial blood flow reduction with positive end-expiratory pressure after acute lung injury in sheep

Smoke inhalation increases bronchial blood flow (Q̇br) and produces edema of the airway system. This study investigates whether the increased Q̇br seen 24 h after inhalation injury can be affected by mechanical ventilation with PEEP (5, 10, 15 cm H₂O). Sheep (n = 8) previously prepared with cardiopulmonary catheters and ultrasonic transit time flow probes mounted around their bronchial arteries were insufflated with four sets of 12 breaths each of cotton smoke. Different levels of PEEP were added to the mechanical ventilation 24 h after injury; each PEEP level was applied for 45 min. There were significant increases in Q̇br and lung lymph flow (Q̇L) associated with a marked decrease in bronchial vascular resistance (BVR) 24 h after injury. However, no change was observed in mean arterial pressure (MAP) or cardiac index (CI). There was a substantial reduction in PaO₂/FIO₂ (P/F), which indicated a deterioration in arterial oxygenation. The application of varying levels of PEEP decreased Q̇br (p < .05) while BVR increased (p < .05), but Q̇L and P/F did not. CI and MAP were recorded. After removal of PEEP, none of the cardiopulmonary variables were significantly different from their postsmoke control values. These findings suggest that mechanical ventilation with PEEP markedly decreases the smoke-induced hyperemia edema frequently seen after inhalation injury without any significant alterations in MAP or CI.