Ventilation with positive end-expiratory airway pressure causes leukocyte retention in human lung

We examined the effect of assisted ventilation with different positive end-expiratory airway pressures (PEEP) on pulmonary leukocyte retention in humans after cardiopulmonary bypass. Eight patients who underwent heart surgery were ventilated in the postoperative phase briefly with 10 (39.6 +/- 0.9 s) and 20 cmH2O (40.3 +/- 1.0 s) PEEP. Before, during, and after this ventilatory maneuver, blood was withdrawn simultaneously from catheters placed in the pulmonary and radial arteries for blood cell differentials. At the same time points, pulmonary and systemic hemodynamics were recorded. During PEEP ventilation, there was a four- (10 cmH2O PEEP) and an eightfold (20 cmH2O PEEP) increase in mixed venous-arterial leukocyte cell difference compared with baseline. This phenomenon was based mainly on a transpulmonary cell difference of polymorphonuclear cells. Likewise, the lymphocytes were entrapped in the pulmonary vasculature during PEEP ventilation. During the ventilatory maneuver, the pulmonary blood flow was significantly reduced; it was indexed by a declined cardiac output. We conclude that PEEP ventilation in the post-operative phase after cardiopulmonary bypass causes pulmonary polymorphonuclear cell entrapment. The most likely mechanism for this phenomenon is the compression of alveolar capillaries and reduced pulmonary blood flow in response to the raised alveolar pressure.