Does positive end-expiratory pressure significantly reduce airway blood flow?

Nutritive (systemic arterial) airway blood flow (mL/min/100 grams tissue) was studied in various size airways at four randomized levels of positive end expiratory pressure (PEEP) in smoke injured and normal lungs. Seven sheep were studied 24 hours after an isolated injury to the left lung using cotton smoke. Radioactive 15-microns microspheres were utilized to measure this airway blood flow. These data demonstrated a marked increase in systemic arterial blood flow to the airways in the injured left lung. Increasing levels of PEEP significantly reduced this hyperemic response. PEEP did not significantly affect the uninjured right lung. Systemic airway blood flow was never reduced to below normal control levels (uninjured) in either lung despite PEEP of up to 20 cm H2O. Severe reduction in airway nutritive flow, and the possibility of airway necrosis, does not appear to occur at PEEP levels of up to 20 cm H2O.