EFFECTS OF DIFFERENT PEEP LEVELS ON MESENTERIC LEUKOCYTE-ENDOTHELIAL INTERACTIONS IN RATS DURING MECHANICAL VENTILATION

INTRODUCTION: Mechanical ventilation with positive end expiratory pressure (PEEP) improves oxygenation and treats acute pulmonary failure. However, increased intrathoracic pressure may cause regional blood flow alterations that may contribute to mesenteric ischemia and gastrointestinal failure. We investigated the effects of different PEEP levels on mesenteric leukocyte-endothelial interactions. METHODS: Forty-four male Wistar rats were initially anesthetized (Pentobarbital I.P. 50mg/kg) and randomly assigned to one of the following groups: 1) NAIVE (only anesthesia; n=9), 2) PEEP 0 (PEEP of 0 cmH(2)O, n=13), 3) PEEP 5 (PEEP of 5 cmH(2)O, n=12), and 4) PEEP 10 (PEEP of 10 cmH(2)O, n=13). Positive end expiratory pressure groups were tracheostomized and mechanically ventilated with a tidal volume of 10 mL/kg, respiratory rate of 70 rpm, and inspired oxygen fraction of 1. Animals were maintained under isoflurane anesthesia. After two hours, laparotomy was performed, and leukocyte-endothelial interactions were evaluated by intravital microscopy. RESULTS: No significant changes were observed in mean arterial blood pressure among groups during the study. Tracheal peak pressure was smaller in PEEP 5 compared with PEEP 0 and PEEP 10 groups (11, 15, and 16 cmH(2)O, respectively; p<0.05). After two hours of MV, there were no differences among NAIVE, PEEP 0 and PEEP 5 groups in the number of rollers (118 +/- 9, 127 +/- 14 and 147 +/- 26 cells/10minutes, respectively), adherent leukocytes (3 +/- 1, 3 +/- 1 and 4 +/- 2 cells/100 mu m venule length, respectively), and migrated leukocytes (2 +/- 1, 2 +/- 1 and 2 +/- 1 cells/5,000 mu m(2), respectively) at the mesentery. However, the PEEP 10 group exhibited an increase in the number of rolling, adherent and migrated leukocytes (188 +/- 15 cells/10 min, 8 +/- 1 cells/100 mu m and 12 +/- 1 cells/5,000 mu m(2), respectively; p<0.05). CONCLUSIONS: High intrathoracic pressure was harmful to mesenteric microcirculation in the experimental model of rats with normal lungs and stable systemic blood pressure, a finding that may have relevance for complications related to mechanical ventilation.