Am. J. Respir. Crit. Care Med., Vol 149, No. 5, 05 1994, 1118-1122.
O2 consumption by the fick method. Methodologic factors
R Chiolero, P Mavrocordatos, D Bracco, Y Schutz, C Cayeux and JP Revelly
Department of Anesthesiology, University Hospital, Lausanne, Switzerland.
This study aimed to compare O2 consumption (VO2) determination by the
gas-exchange (VO2GE) and Fick (VO2F) methods in cardiac surgical patients.
A total of 10 mechanically ventilated postoperative patients were studied
prospectively. Thermodilution was performed using three randomly applied
techniques: room temperature saline injected at end expiration, room
temperature saline randomly injected in the respiratory cycle, and iced
saline injected at end expiration. The influence of the number of
thermodilution determinations was assessed by comparing results from 2 and
10 injections. The variability of VO2F was greater than that of VO2GE.
There was no bias between VO2GE and VO2F values using injectate at room
temperature. Accuracy and precision were not improved by increasing the
number of cardiac output determinations from 2 to 10. A significant bias
was observed using ice- cold injectate, VO2F being 18.0 +/- 15.4 ml/min/m2
lower than VO2GE (p = 0.001). Published results when comparing VO2F and
VO2GE are discrepant. However, a significant bias was found in all studies
using cold injectate, with lower VO2F values. We conclude that iced
injectate should not be used to assess VO2 in critically ill patients.
