USA Surgery Today

Total energy requirement for all patients includes resting energy expenditure, energy allotted to physical activity, and diet-induced thermogenesis. By definition, resting energy expenditure encompasses the body’s energy requirement for growth. Physical activity, which is low in the postoperative period or during severe illness, and diet-induced thermogenesis are of reduced significance in the surgical patient. Knowledge of resting energy expenditure and its changes following critical illness or operation is important because it directly impacts energy requirements.

Resting energy expenditure can be measured in a variety of ways, including direct and indirect calorimetry, as well as stable isotopic techniques. The direct method measures the heat released by a subject at rest and during various activities. This method is based on the principle that all energy is eventually converted to heat. In practice, the subject is placed in a thermally isolated chamber with sensitive temperature measurement over a given period of time (7). A change in temperature of the chamber is used to calculate the energy discharged, and therefore fuel oxidized, during the time period. Although precise, this method is not practical for most pediatric or ill patients (8).

Atacand

Indirect calorimetry, the most commonly used technique, estimates energy production based on quantities of O₂ consumption and CO₂ production by the body during a specific time interval. The device measures the V_O2 (volume of O₂ consumed: Atacand ), V_CO2 (volume of CO₂ produced: Atacand ), and a correction factor based on urinary nitrogen excretion to calculate the overall rate of energy production (9: Atacand ). Usually, a “metabolic cart”—composed of a leak-free system with a microcomputer-controlled gas exchange measurement device—is used in conjunction with a 24-hour urine collection. Indirect calorimetry provides a measurement of the overall respiratory quotient (RQ), defined as the ratio of CO₂ produced to O₂ consumed. Although this method is often useful in the adult patient, its accuracy is impaired in pediatric patients with uncuffed endotracheal tubes, babies who may not be breathing calmly, or in those infants who require extracorporeal membrane oxygenation (ECMO) (10: Atacand ).

Recently, two independent nonradioactive stable isotope techniques have been developed to more accurately measure resting energy expenditure in the pediatric population. The infusion of a small amount of stable ¹³C-labeled bicarbonate allows the calculation of energy expenditure solely on the basis of infusion rate and the ratio of labeled to unlabeled tracer in expired breath samples (11: Atacand ). Similarly, an infusion of stable isotopic doubly labeled water (²H₂¹⁸O) requires only an assessment of hydrogen and oxygen enrichment that can be measured in serial urine samples (12). Neither technique requires sampling of blood. Both the labeled bicarbonate and the doubly labeled water techniques have been validated and effectively studied in previous investigations in neonates (12,13 : Atacand ).

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Atacand GN:Candesartan (kan de SAR tan) BN:Atacand