A predictive equation for determination of resting energy expenditure in mechanically ventilated patients.

STUDY OBJECTIVE

To evaluate an equation that estimates resting energy expenditure from two easily obtained measurements--expired carbon dioxide and minute ventilation, and compare the results of this equation with standard methods of estimating and measuring caloric expenditure in mechanically ventilated patients.

DESIGN

Prospective evaluation in a consecutive, unselected cohort.

SETTING

Medical, surgical, and coronary intensive care units in a university hospital.

PATIENTS

Twenty-five patients (16 to 79 years of age) receiving mechanical ventilation.

INTERVENTION

Indirect calorimetry (IC), minute ventilation (VE), and partial pressure of expired carbon dioxide (PECO2) were obtained on all patients. Harris-Benedict equations were calculated and corrected for known stress factors (HBc). Calculated energy expenditure (CEE) was determined using the following equation: CEE = 9.27 x VE x PECO2 CEE was then compared with IC and HBc.

MEASUREMENTS AND RESULTS

The IC was interpretable in 22 of 25 patients, and CEE was significantly better at estimating caloric requirements than HBc. The mean absolute difference between CEE and IC was significantly less than between HBc and IC (118 +/- 96 vs 302 +/- 269, p < .003). CEE estimated caloric requirements to within 200 kcal of IC in 16 of 22 (72 percent); HBc estimated within 200 kcal of IC in 9 of 22 (41 percent).

CONCLUSIONS

Minute ventilation and expired carbon dioxide measurements are easily and inexpensively obtainable. Energy expenditures calculated from these measurements (CEE) compare favorably with values obtained from a metabolic cart and are significantly more accurate than HBc.