Combination of venoarterial PCO2 difference with arteriovenous O2 content difference to detect anaerobic metabolism in patients.

Abstract

Under conditions of tissue hypoxia total CO2 production (VCO2) should be less reduced than O2 consumption (VO2) since an anaerobic CO2 production should occur. Thus the VCO(2)/VO(2) ratio, and hence the venoarterial CO2 tension difference/arteriovenous O2 content difference ratio (DeltaPCO2/C(a-v)O2), should increase. We tested the value of the DeltaPCO2/C(a-v)O2 ratio in detecting the presence of global anaerobic metabolism as defined by an increase in arterial lactate level above 2 mmol/l (Lac+). Retrospective study over a 17-month period in medical intensive care unit of a university hospital. We obtained 148 sets of measurements in 89 critically ill patients monitored by a pulmonary artery catheter. The DeltaPCO2/C(a-v)O2 ratio was higher in those with increased ( n=73) than in the normolactatemic group (2.0+/-0.9 vs. 1.1+/-0.6, p<0.0001). Among all the O2- and CO2-derived parameters the DeltaPCO2/C(a-v)O2 ratio had the highest correlation with the arterial lactate level ( r=0.57). Moreover, for a threshold value of 1.4 the DeltaPCO2/C(a-v)O2 ratio predicted significantly better than the other parameters (receiver operating characteristic curves) the presence of hyperlactatemia (positive and negative predictive values of 86% and 80%, respectively). The overall survival estimate at 1 month was greater when the DeltaPCO2/C(a-v)O2 ratio was less than 1.4 on the first set of measurements (38+/-10% vs. 20+/-8%, p<0.01). The DeltaPCO2/C(a-v)O2 ratio seems a reliable marker of global anaerobic metabolism. Its calculation would be helpful for a better interpretation of pulmonary artery catheter data.