This review has compared the use of the reverse Fick method and indirect calorimetry for measuring O2 consumption and energy expenditure. Although both are comparable, measurement of V̇O2 by indirect calorimetry tends to provide somewhat higher values than those derived by the Fick equation. This may be due, in part, to the fact that lung parenchymal O2 use is ignored by the Fick method while included in indirect calorimetry. In situations where there is lung injury, the difference may be substantial. Open- and closed- circuit methods of indirect calorimetry each have their advantages which should be considered vis-a-vis the intended application. Estimates of O2 requirements and energy expenditure based on body size, type of injury, or physiologic stress have been shown to be uniformly unsatisfactory in critically ill patients. Thus, for accurate knowledge of V̇O2 in a particular patient, direct measurement is mandated. Indirect calorimetry- determined V̇O2 is more valid than that determined by the Fick equation when examining the relationship between ḊO2 and V̇O2 because indirect calorimetry obviates the problem of 'mathematical coupling.' At the whole- body level, much work remains to be done to elucidate the relationship between ḊO2 and V̇O2, particularly in the setting of critical illness. One area that needs to be addressed is the area of true cellular O2 delivery. Another is the need to identify and measure the tissues most susceptible to ischemia or an imbalance between O2 supply and demand, which requires that whole-body methods be supplemented by measures of regional O2 metabolism.
|Original language||English (US)|
|Number of pages||11|
|Journal||Seminars in Anesthesia|
|State||Published - Jan 1 1994|
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine