The energy costs of surgery as measured by the doubly labeled water (2H218O) method

Energy expenditure before and after surgery was determined in seven patients by the doubly labeled water (2H218O) method (DLW). The values were compared with values obtained by respiratory gas exchange by means of a metabolic measuring cart (MMC). Patients were maintained on total parenteral nutrition before and after trauma. The principal finding was an increase in the rate of CO2 production of 11.9 +/- 5.0% after surgery. This corresponds to a 267 +/- increase in energy expenditure (p less than 0.05). No trauma-associated change in energy expenditure was found with the MMC. The correlation of preoperative values from MMC and DLW was not statistically significant (r = 0.25), nor was the correlation of MMC and the Harris-Benedict equation, but the correlation of DLW with Harris-Benedict equation was statistically significant (r = 0.73, p less than 0.05). We suggest that the discrepancy is because the DLW method measures the cumulative energy expenditure over a period, whereas the MMC gives a "spot" measurement.