Predicted versus measured energy expenditure by continuous, online indirect calorimetry in ventilated, critically ill children during the early postinjury period

Abstract

Objective: Compare the energy expenditure, predicted by anthropometric equations, with that measured by continuous on-line indirect calorimetry in ventilated, critically ill children during the early postinjury period.

Design: Prospective, clinical study.

Setting: Pediatric intensive care unit of a pediatric university hospital.

Patients: A total of 43 ventilated, critically ill children during the first 6 hrs after injury.

Interventions: An indirect calorimeter was used to continuously measure the energy expenditure for 24 hrs.

Measurements and main results: Clinical data collected were age, gender, actual and ideal weight, height, and body surface. Nutritional status was assessed by Waterlow and Shukla Index. Severity of illness was determined by Pediatric Risk of Mortality, Physiologic Stability Index, and Therapeutic Intervention Scoring System. Energy expenditure was measured (MEE) by continuous on-line indirect calorimetry for 24 hrs. Predicted Energy Expenditure (PEE) was calculated using the Harris-Benedict, Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Maffeis, Fleisch, Kleiber, Dreyer, and Hunter equations, using the actual and ideal weight. MEE and PEE were compared using paired Student's t-test, linear correlation (r), intraclass correlation coefficient (pI), and the Bland-Altman method. Mean MEE resulted in 674 +/- 384 kcal/day. Most of the predictive equations overestimated MEE in ventilated, critically ill children during the early postinjury period. MEE and PEE differed significantly (p<.05) except when the Caldwell-Kennedy and the Fleisch equations were used. r2 ranged from 0.78 to 0.81 (p<.05), and pI was excellent (>.75) for the Caldwell-Kennedy, Schofield, Food and Agriculture/World Health Organization/United Nation Union, Fleisch, and Kleiber equations. The Bland-Altman method showed poor accuracy; the Caldwell-Kennedy equation was the best predictor of energy expenditure (bias, 38 kcal/day; precision, +/- 179 kcal/day). The accuracy in the medical group was higher (pI range,.71-.94) than in surgical patients (pI range,.18-.75).

Conclusions: Predictive equations do not accurately predict energy expenditure in ventilated, critically ill children during the early postinjury period; if available, indirect calorimetry must be performed.