BJA Advance Access originally published online on November 22, 2006
British Journal of Anaesthesia 2007 98(1):45-52; doi:10.1093/bja/ael310
Non-invasive metabolic monitoring of patients under anaesthesia by continuous indirect calorimetry—an in vivo trial of a new method
1 Department of Electrical and Computer Systems Engineering, Faculty of Engineering, Monash University Victoria, Australia
2 Department of Anaesthesia, The Austin Hospital Heidelberg, Victoria 3084, Australia
3 Department of Anaesthesia and Perioperative Medicine The Alfred, Melbourne, Victoria 3004, Australia
*Corresponding author: Department of Electrical & Computer System Engineering, Clayton Campus, Building 72, Monash University, VIC 3800, Australia. E-mail: Christopher.Stuart-Andrews{at}eng.monash.edu.au
Background. Oxygen uptake is an important form of metabolic monitoring for patients under anaesthesia. In critically ill patients oxygen uptake has been shown to provide valuable clinical information in directed therapy and acts as a useful monitor of cardiovascular dysfunction. A new method of continuous real time monitoring of metabolic gas exchange was tested in patients during anaesthesia.
Methods. Using a standard anaesthetic machine with attached semi-closed circle absorber system, oxygen uptake was measured continuously throughout surgery in 30 patients undergoing cardiopulmonary bypass surgery and compared with paired measurements made with the reverse Fick method. The method is an indirect calorimetry technique which uses fresh gas rotameters for control, regulation and measurement of the gas flows into the system, with continuous sampling of mixed exhaust gas.
Results. When compared with the reverse Fick method the oxygen uptake showed a mean difference (and SD) of 20.7 ml min–1 or 12.1% (25.3 ml min–1) pre-bypass and 13.9 ml min–1 or 8.1% (27.0 ml min–1) post-bypass. This bias is consistent with previous studies comparing oxygen uptake measured at the mouth against oxygen uptake by reverse Fick, which have shown a difference of approximately 10–15% accounted for by the consumption of oxygen by lung tissue.
Conclusions. As the method allows continuous measurement of gas exchange and can be adapted to a modern anaesthetic workstation it is an attractive method for use in clinical setting.