Perioperative changes in oxygen consumption: estimations from minimal-invasive cardiac output and a-cvO2 difference parallel to indirect calorimetry

Feasible estimations of perioperative changes in oxygen consumption could enable larger studies of its role in postoperative outcomes. Current methods, by pulmonary artery catheterisation or breathing gas analysis, are often regarded as either invasive or technically requiring. In this pilot study, we investigated the relationship between estimations of oxygen consumption, based on minimal-invasive cardiac output and arterial-central venous blood gas sampling, and indirect calorimetry in the perioperative period using the data collected during a clinical trial on perioperative oxygen transport. In 20 patients >65 years during epidural and general anaesthesia for open abdominal surgery, Fick-based estimations of oxygen consumption(EVO2), the product of cardiac output from LiDCOplus(LiDCO Ltd, Cambridge, UK) and arterial-central venous oxygen content difference, were compared with indirect calorimetry(GVO2) using QuarkRMR(COSMED, srl. Italy). Eighty-five simultaneous intra- and postoperative measurements at different time-points were analysed for prediction, parallelity and by traditional agreement assessment. There was an overall association between GVO2 and EVO2, 73(95% CI 62 to 83) + 0.45(95% CI 0.29 to 0.61) EVO2 ml min-1m-2, P<0.0001. GVO2 and EVO2 changed in parallel intra- and postoperatively when normalised to their respective overall means. Unadjusted mean difference between GVO2 and EVO2 indexed for body surface area was 26(95% CI 20 to 32) with limits of agreement (1.96SD) of -32 to 85 ml min-1m-2 and did not change over time. There was low correlation for absolute agreement, ICC(A,1) 0.37(95% CI 0.34 to 0.65) [F(84,10.2)=3.07, P=0.0266]. Despite lack of absolute agreement, the estimated oxygen consumption changed in parallel to the metabolic measurements in the perioperative period. Prediction or trending of oxygen consumption by this or similar methods could be further evaluated in larger samples.