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 rpoduction of 11.9 ± 5.0% after surgery. This corresponds to a 267 ± increase in energy expenditure (p < 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 < 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.