A comparison between ventilation modes: how does activity level affect energy expenditure estimates?

BACKGROUND

An appropriate diet is essential to avoid complications of overfeeding or underfeeding in mechanically ventilated intensive care unit (ICU) patients. The paucity of consistent comparative data on energy expenditure for each ventilation mode complicates diet prescription. This study evaluates caloric requirements by comparing estimated and measured energy expenditure values for 2 ventilation modes.

METHODS

The energy expenditure of 100 ICU patients on assisted or controlled mechanical ventilation was measured by indirect calorimetry for 20 minutes. Values were calculated for a 24-hour period and compared with Harris-Benedict estimates multiplied by an injury factor and either multiplied or not by a 10% activity factor.

RESULTS

The mean Harris-Benedict estimate was 1858.87 +/- 488.67 kcal/24 h when multiplied by an injury factor and a 10% activity factor. The mean energy expenditure values measured by indirect calorimetry were 1712.76 +/- 491.95 kcal/24 h for controlled and 1867.33 +/- 542.67 kcal/24 h for assisted ventilation. The mean total energy expenditure for assisted ventilation was 10.71% greater than the mean for controlled ventilation (P < .001). For controlled ventilation, Harris-Benedict results overestimated indirect calorimetry values by 141.10 +/- 10 kcal/24 h (8.2%, P = .012) when multiplied by injury and activity factors, and underestimated values by 44.28 +/- 28 kcal/24 h (2.6%, P = .399) when the equation was calculated without the activity factor. For assisted ventilation, Harris-Benedict results underestimated indirect calorimetry values by 198.84 +/- 84 kcal/24 h (10.7%, P = .001) when not multiplied by the activity factor and by 13.46 kcal/24 h (0.75%) when the activity factor was used, but differences were not statistically significant (P = .829).

CONCLUSIONS

Results suggest that a 10% activity factor should be adopted only for assisted ventilation because multiplication by an activity factor may lead to overfeeding of patients on controlled ventilation.