Indirect calorimetry in mechanically ventilated infants and children: accuracy of total daily energy expenditure with 2 hour measurements

Objective: To determine how accurately total daily energy expenditure can be estimated from measurement periods of less than 24 h in mechanically ventilated infants and children. Design: Prospective study to validate a method to determine energy expenditure. Setting: Pediatric intensive care unit of an university hospital. Patients: Nineteen ventilated patients (age 3 weeks - 13 years) with a FiO(2) of less than 60% and tube leakage < 10% (the difference between inspiratory and expiratory tidal volume measured by the ventilator). Separately, in five patients with varying tube leakage (2-59%) the influence of tube leakage on measured energy expenditure was determined, Measurements: Energy expenditure was measured by indirect calorimetry. Total daily energy expenditure measurements for 24 h were compared with 2 h energy expenditure measurements. The influence of body temperature on measured energy expenditure was determined. Results: The mean coefficient of variation among 2 hour periods of measured energy expenditure was 6% (range 2-11%) compared with total daily energy expenditure measurements. The influence of body temperature revealed an increase of 6% of energy expenditure/degrees C. An increased tube leakage influenced the energy expenditure measurements significantly (P < 0.001). Conclusion: In a clinical situation in patients with a tube leakage < 10% total daily energy expenditure can be estimated from a 2 h measurement period.