THE METABOLIC RESPONSE TO OPERATIVE STRESS IN INFANTS

The aim of this study was to characterize energy metabolism and substrate utilization in infants following an operation. Nineteen infants (weight 3.2±0.2 kg) who had an operation were studied. Anesthesia was standardized and operative stress score (OSS) was recorded. Five infants had a minor operation (OSS<7), and 14 infants had a major operation (OSS≥7). Energy and nitrogen intake were constant during the 48-hour study period. Respiratory gas exchange was measured by indirect calorimetry preoperatively, and postoperatively for the first 12 hours continuously and at 24 hours, 48 hours, and 5 days. Urinary nitrogen excretion rate was measured for the first 48 hours following the operation. Physical activity was scored. Resting energy expenditure (REE) and nonprotein respiratory quotient (NPRQ) were calculated. REE increased postoperatively, peaking at 2 to 4 hours, and returned to baseline levels by 12 to 24 hours. Peak REE was significantly higher than baseline REE (P<.001). Substrate utilization was not altered by operation. The increase in REE was significantly greater in infants having a major operation than in infants having a minor operation (P<.05). Among infants having a major operation, the increase in REE was significantly greater in those infants more than 48 hours old, than in those infants less than 48 hours old (P<.05). From this study we conclude that in newborn infants there is a modest and short-lived postoperative increase in REE, that the size of the increase in REE is related to the severity of the operation, and that the increase in REE is reduced in infants less than 48 hours old. © 1993 W.B. Saunders Company. All rights reserved.