Effect of positive end-expiratory pressure on splanchnic perfusion in acute lung injury.

Abstract

To evaluate the acute effects of an increased positive end-expiratory pressure (PEEP) on splanchnic tissue perfusion. Clinical prospective study. Intensive care unit in a university clinic. Six patients with severe acute lung injury (ALI) requiring mechanical ventilation. All patients had bilateral infiltrates in chest X-ray, PaO2/FiO2 < 200 mmHg and stable hemodynamics without vasoactive drugs. PEEP was increased by 5 cmH2O from a clinically selected PEEP level (8/6-11 cmH2O) up to (13/10-14 cmH2O) followed by a return to baseline. Splanchnic blood flow was measured using primed continuous infusion of indocyanine green dye with hepatic venous sampling and systemic hemodynamics by routine monitoring. In addition, we estimated gastric mucosal-arterial PCO2 difference and splanchnic lactate/pyruvate exchange. After a baseline measurement, PEEP was increased. After 60 min all measurements were repeated. PEEP was returned to the baseline level and a third measurement followed. PEEP had no effect on cardiac index (baseline I: 3.2/6.1-2.5 l/min/m2; PEEP: 3.3/5.7-2.3 l/min/m2; baseline II: 3.4/6.0-2.5 l/min/m2); neither did PEEP have any effect on splanchnic blood flow (baseline I: 0.91/1.39-0.62 l/min/m2; PEEP: 1.04/1.75-0.54 l/min/m2; baseline II: 1.07/1.42-0.68 l/min/m2, respectively) or perfusion (gastric mucosal-arterial PCO2 difference baseline I: 2.1/12.8-0.6 kPa; PEEP: 1.7/14.5-0.7 kPa; baseline II: 1.7/8.8-0.1 kPa; lactate uptake baseline I: 0.5/1.1-0.3 mmol/min/m2; PEEP: 0.4/1.0-0.3 mmol/min/m2; baseline II: 0.5/0.9-0.3 mmol/min/m2; hepatic venous lactate/pyruvate baseline I: 9.7/10.6-5.7; PEEP: 9.7/14.2-6.4; baseline II: 8.4/12.4-7.3; respectively). PEEP by itself does not have a consistent effect on splanchnic blood flow and metabolism when cardiac index is stable and patients are ventilated within the linear part of the pv curve.