Leukocyte – endothelial interactions in mesenteric microcirculation of rats under different positive end expiratory pressure levels

Introduction

Mechanical ventilation (MV) with positive end expiratory pressure (PEEP) is widely used to improve oxygenation and to treat acute respiratory failure. PEEP can affect nearly every organ system of the body due to homeostatic interactions between the lungs and other body systems. Although essential in the management of critically ill patients, many deleterious side effects of positive pressure ventilation in the lungs and hemodynamics have been reported.

Methods

This study investigated the effects of different PEEP levels on leukocyte – endothelial interactions in postcapillaric venules (13–23 μm diameter) at the mesentery by intravital microscopy and lung histomorphometry. Nineteen male Wistar rats were submitted to inhaled isofluorane anesthesia and MV with a tidal volume of 10 ml/kg, a respiratory rate of 70 breaths/min and FiO₂ = 100%. Animals were randomly assigned to three groups: (1) PEEP0 (n = 6), no PEEP; (2) PEEP5, 5 cmH₂O (n = 6); and (3) PEEP10, 10 cmH₂O (n = 7).

Results

After 2 hours of MV, there were no differences between PEEP0 and PEEP5 in the number of rolling leukocytes/10 minutes (127 ± 16 and 147 ± 26, respectively), adherent leukocytes/100 μm (3 ± 1 and 4 ± 2, respectively), migrated leukocytes into the perivascular tissue/5,000 μm² (2 ± 1 and 2 ± 1, respectively) and total white blood cells/mm³ (11,730 ± 2,856 and 10,200 ± 2,222, respectively). However, the PEEP10 group presented an increased number of rolling leukocytes (188 ± 15 cells/10 min, P < 0.05), adherent leukocytes (8 ± 1 cells/100 μm, P < 0.05), migrated leukocytes (12 ± 1 cells/5,000 μm², P < 0.05) at the mesentery, and an increased number of total white blood cells (18,786 ± 4,207 cells/mm³, P < 0.05), basically neutrophils. Lung morphometric analysis showed some edema at the perivascular tissue with no neutrophil infiltration in the parenchyma of the PEEP10 group compared with the other groups (P < 0.05). There were no changes in mean arterial blood pressure in all groups along the study period.

Conclusion

After 2 hours of MV, PEEP = 10 cmH₂O induced an inflammatory response in rat mesenteric microcirculation.