Oxygen consumption and lactate release by the lung after cardiopulmonary bypass and during septic shock

We sought to determine whether a correlation exists between lung lactate release and lung oxygen consumption by studying adult intensive care patients, either after cardiopulmonary bypass (CPB) or with septic shock.

A prospective observational study of six post cardiopulmonary bypass patients and seven patients with septic shock was performed in an intensive care unit of a major teaching hospital. Pulmonary oxygen consumption was estimated by subtracting oxygen consumption calculated using the reverse Fick equation (V O2Fick) from that measured by indirect calorimetry (V O2meas). Pulmonary lactate release was derived from the difference between arterial and mixed-venous lactate, multiplied by cardiac output.

Pulmonary oxygen consumption comprised a substantial component of total oxygen consumption (CPB-median: 20.6%; interquartile range (IQR): 15.4 - 27.3%; septic shock-median: 32.3%; IQR: -4.0 - 35.4%). Lung lactate release occurred both after CPB (median: 27.5 mmol/hr; IQR: 24.8-64.1 mmol/hr) and with septic shock (median: 55.4 mmol/hr; IQR: 24.3 - 217.6 mmol/hr). Although no correlation was found between lung lactate release and pulmonary oxygen consumption, lactate release correlated with V O2meas and V O2Fick in septic patients (p < 0.005).

We conclude that lung oxygen consumption and lactate release are substantial in conditions associated with lung inflammation. Lactate release and lung oxygen consumption may not share a common pathogenesis, however there is an association between lung lactate release and systemic oxygen consumption in sepsis.