Peri-operative oxygen consumption revisited

BACKGROUND Monitoring oxygen consumption (VO 2 ) is neither recommended nor included in peri-operative haemodynamic algorithms aiming at optimising oxygen delivery (DO 2 ) in major abdominal surgery. Estimates of peri-operative VO 2 changes are uncertain in earlier publications and have limited generalisability in the current high-risk surgical population. In a prospective non-interventional observational study in elderly patients undergoing major abdominal procedures, we investigated the change of VO 2 after induction of anaesthesia and secondarily, the further changes during and after surgery in relation to DO 2 and estimated oxygen extraction ratio (O 2 ER) by routine monitoring. METHODS VO 2 was determined by indirect calorimetry (QuarkRMR) in 20 patients more than 65 years (ASA II to IV), scheduled for elective open upper abdominal surgery with combined epidural and general anaesthesia. Data were collected during 20-minute periods pre-operatively and after anaesthesia induction, with subsequent measurements during surgery and postoperatively. Simultaneously, DO 2 was monitored using LiDCOplus. The O 2 ER was estimated from arterial–central venous oxygen content calculation. Mixed models were used to analyse the peri-operative changes. RESULTS VO 2 decreased after induction of anaesthesia by a mean of 34% (95% CI, 28 to 39). After 2 h of surgery, VO 2 was reduced by 24% (95% CI, 20 to 27) compared with the awake baseline measurements. Pre-operative mean DO 2 was 440 (95% CI, 396 to 483) ml min −1 m −2 and decreased by a mean of 37% (95% CI, 30 to 43) during anaesthesia. The estimated O 2 ER did not change intra-operatively 0.24 (95% CI, 0.21 to 0.26) but increased postoperatively to 0.31 (95% CI, 0.27 to 0.36). The changes of VO 2 were parallel with changes of DO 2 and O 2 ER in the intra-operative period. CONCLUSION General anaesthesia reduced VO 2 by approximately a third in elderly patients undergoing major abdominal surgery. Parallel changes of intra-operative VO 2 and delivery were demonstrated while oxygen extraction was low. The relevance of these changes needs further assessment in relation to outcomes and haemodynamic interventions. TRIAL REGISTRATION Clinicaltrials.gov NCT 03355118.