Energy expenditure and fluid and electrolyte requirements in anesthetized infants and children.

In 31 infants and children (body weights ranging from 3.8 to 25 kg), indirect calorimetry was used for the calculation of energy needs (E, kcal/h), fluid volume (FV, ml/h) and electrolyte requirements (sodium, Na+, and potassium, K+, mmol/liter per hour) during halothane anesthesia. The children were spontaneously breathing and undergoing minor lower abdominal or orthopedic surgery. A nonrebreathing anesthesia circuit was used, and gas concentrations were measured by a mass spectrometer. For the evaluation of ventilation during periods of measurements, pneumotachography and in-line capnography were used. Energy expenditure was related to weight and followed the regression equation E = 1.5 X kg + 5.2; r = 0.96. The energy needs were converted to fluid volumes according to the water requirements for heat production, which resulted in the following relationship between FV and weight: FV = 2.4 X kg + 8.6; r = 0.96. The energy expenditure was up to 50% lower than in previous reports. Extrapolations of energy needs from awake values are inappropriate to use during halothane anesthesia. Because of the low energy expenditure during anesthesia, requirements of sodium and potassium were up to 50% lower than those based on previous standards.