Pulmonary lactate release in patients with sepsis and the adult respiratory distress syndrome

Purpose: Elevated arterial lactate concentrations in patients with sepsis have been interpreted as evidence of peripheral, nonpulmonary tissue hypoxia. These patients often develop pulmonary failure manifested by the acute respiratory distress syndrome (ARDS). As the result of tissue hypoxia or inflammation, the lungs of patients with sepsis and ARDS may become a source of lactate release into the circulation. Materials and methods: Pulmonary lactate release was measured in 19 patients with sepsis, arterial lactate greater than or equal to 2.2 mm, and gastric mucosal pH > 7.30. A normal gastric mucosal pH served as a marker of adequate splanchnic oxygenation. Pulmonary lactate release was computed as the product of the cardiac index and the difference in plasma L-lactate concentration in simultaneously obtained arterial and mixed venous blood samples. Lung injury was graded with the Lung Injury Score using radiographic and physiologic data. Results: The lungs of patients with minimal or no lung injury (lung injury score < 1) produced significantly less lactate than those with moderate or severe lung injury (lung injury score greater than or equal to 1) (P < .005). The Lung Injury Score correlated with pulmonary lactate release (r(2) = .73; P < .0001). This relationship resulted primarily from increases in mixed venous-arterial lactate differences (r(2) = .59). The Lung Injury Score correlated weakly with the cardiac index (r(2) = .32). Arterial lactate concentration did not correlate with pulmonary lactate release, systemic oxygen transport, or systemic oxygen consumption. Conclusions: The lungs of patients with sepsis and ARDS may produce lactate. Pulmonary lactate release correlates with the severity of lung injury. The contribution of pulmonary lactate release should be considered when interpreting arterial lactate concentration as an index of systemic hypoxia. (C) 1996 by W.B. Saunders Company