Oxygen consumption, energy expenditure, and substrate utilization after cardiac surgery in children

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Abstract
To determine the oxygen consumption (VO2), resting energy expenditure, and substrate utilization after cardiac surgery in children. Prospective, observational, cross-sectional study with factorial design. Pediatric ICU at a university hospital. Twenty-six consecutive children during the first 3 days after open-heart surgery. Patients were mechanically ventilated and received routine therapeutic interventions. VO2, resting energy expenditure, and substrate utilization were determined by indirect calorimetry. Cardiac index was calculated using the Fick equation from the measured VO2 and the arterial-mixed venous oxygen content difference, and this cardiac index value was compared with a simultaneous cardiac index value that was measured by thermodilution whenever possible. There were excellent correlation and agreement between cardiac index measurements by Fick equation and thermodilution, indicating accurate VO2 measurements. VO2 was consistent with predicted values in healthy resting children. Resting energy expenditure was consistent with the predicted basal metabolic rate. The mean caloric intake was 19% of the mean energy expenditure. The respiratory quotient was 0.74 +/- 0.05. The substrate utilization showed a shift toward fat oxidation and either gluconeogenesis or impaired carbohydrate utilization. Cardiovascular surgery in children does not significantly alter resting energy expenditure but influences the substrate utilization. Perioperative hormonal stress responses and therapeutically administered catecholamines may explain the shift toward fat oxidation.

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