Calculated and measured oxygen consumption in mechanically ventilated surgical patients in the early post-operative period

Oxygen consumption ((V) over dot o(2)) measured by indirect calorimetry (Nellcor-Puritan-Bennett 7250; Carlsbad, CA, USA) has been compared with (V) over dot o(2) calculated by the Fick method in 22 volume-controlled ventilated general surgical patients in the early post-operative period. For 198 pairs of measurements, (V) over dot o(2) Fick and (V) over dot o(2) indirect calorimetry correlated significantly (y=1.00x-35.8, P=0.0001, r=0.77). (V) over dot o(2) indirect calorimetry was 212 +/- 32 mL min(-1) and (V) over dot o(2) Fick was 177 +/- 41 mL min(-1) (P=0.0001). The bias was 35 +/- 26 mL min(-1). This difference represents 16 +/- 13% of the total body (V) over dot o(2). (V) over dot o(2) calculated by the Fick method did not accurately predict (V) over dot o(2) measured by indirect calorimetry, and the two methods were not interchangeable. (V) over dot o(2) calculated by the Fick method underestimated (V) over dot o(2) as measured by indirect calorimetry by a systematic quantity that could be attributed, in part, to (V) over dot o(2) of the lung. Indirect calorimetry should be the preferred method for measuring total body (V) over dot o(2) in mechanically ventilated surgical patients.