In this study, the rates of lipid mobilization and of lipolysis have been quantified in severely burned children. In all 12 patients studied, the basal rates were determined. In seven patients, the lipolytic responsiveness to an infusion of epinephrine (0.015 μg/kg/min) was tested, and in the other five patients, the response to beta-adrenergic blockade (propranolol, 1 mg/kg) was tested. The rate of appearance (Ra) of free fatty acids (FFA) was quantified by means of the infusion of 1-13C-palmitate to determine the rate of lipid mobilization, and Ra glycerol was determined using d5-glycerol to assess the rate of lipolysis more directly. In five patients, body composition was determined after recovery by means of H218O dilution. The basal rate of lipolysis was higher than normal in the burned children. In four of the seven patients infused with epinephrine, there was a pronounced increase in Ra glycerol. In all patients given beta-blockade, Ra glycerol decreased greatly. Changes in Ra FFA corresponded with the changes in Ra glycerol in each case. Total body fat was very low (approximately 2% body weight), reflecting the surgical removal of fat in the process of burn wound excision. From these data it is concluded that lipolytic responsiveness to catecholamines in severely burned children is variable, but not absent, despite chronically elevated levels of catecholamines. The total extent of lipolysis may be limited by the available fat mass in children treated with fascial excision. In such patients, the limitation in the ability to mobilize an adequate amount of FFA to fully meet energy requirements provides an important rationale for the clinical practice of providing nutritional support in hourly boluses, as opposed to infrequent meals, since any period of even a few hours in which nutrients are not being absorbed will result in an energy substrate deficiency and consequent increase in amino acid oxidation.
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