British Journal of Anaesthesia, 2003, Vol. 90, No. 3 281-290
© 2003 The Board of Management and Trustees of the British Journal of Anaesthesia
Laboratory Investigations |
Accuracy of feedback-controlled oxygen delivery into a closed anaesthesia circuit for measurement of oxygen consumption
1 Department of Anaesthesiology, University-Hospital Düsseldorf, Moorenstrasse 5, D-40225 Düsseldorf, Germany. 2 Department of Anaesthesiology, Merheim Hospital, D-51109 Cologne, Germany
Corresponding author. Email: achim.schindler@uni-duesseldorf.de 
Results were presented in part at the ‘47. Deutscher Anaesthesiekongress’, Munich 2000, and at the 8th Annual Congress of the European Society of Anaesthesiologists, Gothenburg, Sweden 2001.
Background. Oxygen consumption (V·>O2) is rarely measured during anaesthesia, probably because of technical difficulties. Theoretically, oxygen delivery into a closed anaesthesia circuit (V·>O2-PF; PhysioFlexTM Draeger Medical Company, Germany) should measure V·>O2. We aimed to measure V·>O2-PF in vitro and in vivo.
Methods. Three sets of experiments were performed. V·>O2-PF was assessed with five values of V·>O2 (0–300 ml min–1) simulated by a calibrated lung model (V·>O2-Model) at five values of FIO2 (0.25–0.85). The time taken for V·>O2-PF to respond to changes in V·>O2-Model gave a measure of dynamic performance. In six healthy anaesthetized dogs we compared V·>O2-PF with V·>O2 measured by the Fick method (V·>O2-Fick) during ventilation with nine values of FIO2 (0.21–1.00). V·>O2-PF and V·>O2-Fick were also compared in three dogs when V·>O2 was changed pharmacologically [102 (SD 14), 121 (17) and 200 (57) ml min–1]. In patients during surgery, we measured V·>O2-PF and V·>O2-Fick simultaneously after induction of anaesthesia (n=21) and during surgery (n=17) (FIO2 0.3–0.5).
Results. Compared with V·>O2-Model, V·>O2-PF values varied from time to time so that averaging over 10 min is recommended. Furthermore, at an FIO2 >0.8, V·>O2-PF always overestimated V·>O2. With FIO2 <0.8, averaged V·>O2-PF corresponded to V·>O2-Model and adapted rapidly to changes. Averaged V·>O2-PF also corresponded to V·>O2-Fick in dogs at FIO2 <0.8. V·>O2 measured by the two methods gave similar results when V·>O2 was changed pharmacologically. In contrast, V·>O2-PF systematically overestimated V·>O2-Fick in patients by 52 (SD 40) ml min–1 and this bias increased with smaller arteriovenous differences in oxygen content.
Conclusion. V·>O2-PF measures V·>O2 adequately within specific conditions.
Br J Anaesth 2003; 90: 281–90
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