Comparison of oxygen consumption measurements: indirect calorimetry versus the reversed Fick method.
OBJECTIVE
To compare measurement of oxygen consumption (VO2) by spirometry and the reversed Fick method.


METHODS
Within-patient comparison using simultaneous measurements by the two methods, one previously calibrated on a metabolic simulator.


METHODS
Twenty sets of observations on eight patients (57 to 83 yrs) requiring mechanical ventilation in a critical care unit.


METHODS
None during or immediately before the measurements.


RESULTS
Duplicate pairs of measurements of VO2 were made with a previously validated spirometric technique and the reversed Fick method (Qt[CaO2 - CVO2]), where Qt is cardiac output, CaO2 is arterial oxygen content, and CVO2 is mixed venous oxygen content. The coefficient of variation of the difference between duplicate measurements by the former technique was only 2.53% compared with 10.4% for the latter. The mean VO2 measurement by the spirometric method was 285.7 +/- 40.7 (SD) mL/min standard temperature and pressure, dry (STPD) and for the reversed Fick method, the mean VO2 measurement was 249.3 +/- 38.5 mL/min STPD. The mean difference was 36.4 +/- 28.5 mL/min STPD (p less than .001).


CONCLUSIONS
The repeatability of the spirometric method was four times better than the reversed Fick method. The latter gave a significantly lower value that probably, in part, reflects the VO2 of the lung, which is included in the spirometric method but not in the reversed Fick measurement.
Division of Anaesthesia, Clinical Research Centre, Harrow, Middlesex, UK.
M N
MN
Smithies
B
B
Royston
K
K
Makita
K
K
Konieczko
J F
JF
Nunn
D000368:Aged; D000369:Aged, 80 and over; D002153:Calorimetry, Indirect; D002302:Cardiac Output; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D015203:Reproducibility of Results; D013147:Spirometry
D010100:Oxygen