Objective To examine the role of targeted indirect calorimetry in detecting the adequacy of energy intake and the risk of cumulative energy imbalance in a subgroup of critically ill children suspected to have alterations in resting energy expenditure. We examined the accuracy of standard equations used for estimating resting energy expenditure in relation to measured resting energy expenditure in relation to measured resting energy expenditure and cumulative energy balance over 1 week in this cohort. Design A prospective cohort study. Setting Pediatric intensive care unit in a tertiary academic center. Interventions A subgroup of critically ill children in the pediatric intensive care unit was selected using a set of criteria for targeted indirect calorimetry. Measurements Measured resting energy expenditure from indirect calorimetry and estimated resting energy expenditure from standard equations were obtained. The metabolic state of each patient was assigned as hypermetabolic (measured resting energy expenditure/estimated resting energy expenditure >110%), hypometabolic (measured resting energy expenditure/estimated resting energy expenditure <90%), or normal (measured resting energy expenditure/estimated resting energy expenditure = 90– 110%). Clinical variables associated with metabolic state and factors influencing the adequacy of energy intake were examined. Main Results Children identified by criteria for targeted indirect calorimetry, had a median length of stay of 44 days, a high incidence (72%) of metabolic instability and alterations in resting energy expenditure with a predominance of hypometabolism in those admitted to the medical service. Physicians failed to accurately predict the true metabolic state in a majority (62%) of patients. Standard equations overestimated the energy expenditure and a high incidence of overfeeding (83%) with cumulative energy excess of up to 8000 kcal/week was observed, especially in children <1 yr of age. We did not find a correlation between energy balance and respiratory quotient (RQ) in our study. Conclusions We detected a high incidence of overfeeding in a subgroup of critically ill children using targeted indirect calorimetry The predominance of hypometabolism, failure of physicians to correctly predict metabolic state, use of stress factors, and inaccuracy of standard equations all contributed to overfeeding in this cohort. Critically ill children, especially those with a longer stay in the PICU, are at a risk of unintended overfeeding with cumulative energy excess.

Oxidation of L[1-13C]methionine ([13C]-Met) in liver mitochondria can be quantified by measuring exhaled 13CO2. We hypothesized that 13CO2 recovery after i.v. administered [13C]-Met would provide a noninvasive measure of liver function in pediatric intestinal failure-associated liver disease (IFALD). After Institutional Review Board (IRB) approval, 27 patients underwent L[1-13C]-Met breath tests ([13C]-MBTs), five of whom underwent repeat testing after clinical changes in liver function. Sterile, pyrogen-free [13C]-Met was given i.v. Six breath samples collected during 120 min were analyzed for 13CO2 enrichment using isotope ratio mass spectrometry. Pediatric end-stage liver disease (PELD) scores were recorded, and total carbon dioxide (CO2) production was measured by indirect calorimetry. Twenty-seven patients (median age = 5.3 mo) underwent a total of 34 [13C]-MBTs without adverse events. Fourteen patients had documented liver biopsies (five with cirrhosis and nine with cholestasis or fibrosis). The [13C]-MBT differentiated patients with and without cirrhosis (medians 210 and 350, respectively, p = 0.04). Serial [13C]-MBTs in five patients reflected changing PELD scores. i.v. administering the stable isotope [13C]-Met with serial breath sampling provides a useful, safe, and potentially clinically relevant evaluation of hepatic function in pediatric IFALD. The [13C]-MBT may also help quantify progression or improvement of IFALD.