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

Objective: To evaluate the acute effects of an increased positive end-expiratory pressure (PEEP) on splanchnic tissue perfusion.¶Design: Clinical prospective study.¶Setting: Intensive care unit in a university clinic.¶Patients: 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.¶Interventions: 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.¶Measurements and main results: 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).¶Conclusion: 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.