Increased intrapulmonary oxygen consumption in mechanically ventilated patients with pneumonia

Pulmonary oxygen consumption (V(O2)pulm) is believed to be increased in patients with lung infection. In the present study, VO2pulm was estimated from the difference between total oxygen consumption measured with indirect calorimetry (V(O2)cal) and oxygen consumption assessed with the reverse Fick method (V(O2)Fick). Seventy-five patients requiring mechanical ventilation were included, and were divided for analysis into two groups according to the existence (n = 41) or absence (n = 34) of pneumonia. V(O2)pulm was correlated with various parameters of impaired lung function. To assess the metabolic function of the lung, the differences in lactate and glucose concentrations at different arterial-mixed venous concentrations were determined and transpulmonary lactate flux as well as glucose flux was calculated. As compared with V(O2)pulm in patients without pneumonia (19.4 +/- 1.2 ml/ min/m2), V(O2)pulm was significantly increased in patients with pneumonia (50.7 +/- 1.7 ml/min/m2 (p < 0.001). For intrapatient measurements of V(O2)pulm, a sufficient reproducibility was achieved. V(O2)pulm increased with the lung injury score, number of afflicted lobes, venous admixture, the transpulmonary lactate flux, and the transpulmonary glucose flux, respectively. We speculate that the increased V(O2)pulm of infected lungs is due to different mechanisms, including increased oxidative metabolism by essentially extrapulmonary structures such as neutrophils and macrophages, as well as by changes in the metabolic function of lung tissue itself.