Experimental and clinical tests of the oxyconsumeter: a new oxygen uptake monitor

The prototype of a microprocessor controlled oxygen uptake monitor oxyconsumeter developed by Draegerwerk AG, Luebeck, FRG, has been tested. The measuring accuracy of this device was assessed with laboratory bench experiments utilizing both the nitrogen dilution technique and the hydrogen combustion technique to simulate oxygen uptake (VO2). The correlation coefficient between the simulated and the measured VO2 values was 0.9989 (p less than 0.05, n = 115). The average relative error of the VO2 values was -3.32% +/- 3.88% when breathing 21 vol% oxygen and -5.58% +/- 4.53% for 70 vol% oxygen (percent of reading). This was within the range given by the manufacturer (+/- 5% for 21 vol% to less than 40 vol%, +/- 10% for 40 vol% to less than 70 vol%) with few exceptions. Furthermore the oxyconsumeter was used in clinical experiments to determine oxygen uptake during general anaesthesia. Oxygen uptake was monitored using a non-rebreathing system with an externally triggered expiratory valve. The difference between preanaesthetic reference values and values determined during anaesthesia averaged -24.8 +/- 20.1 ml/min/m2 oxygen. This average relative change of -16.0 +/- 11.5% was statistically significant in 11 of 15 cases (p less than 0.05).