Stratification of injury severity using energy expenditure response in surgical infants

Injury severity stratification has important clinical outcome significance and can influence nutritional management. Although surgery alone has been shown not to increase measured energy expenditure (MEE) substantially, large increases in MEE can result from severe underlying acute illness, which frequently necessitates surgery (like sepsis or intense inflammation). The authors hypothesized that the magnitude and duration of the MEE response to surgery associated with a severe preoperative acute injury would exceed that of surgery in which no substantial preoperative stress was present, thus representing an index of overall injury severity in surgical infants.

MEE (kcal/kg/d) was determined on postoperative days (POD) 2, 5, and 8 in 12 infants (average age, 47 days) after two separate injury insults (at least 8 days apart). In each patient, one operation resulted in a peak serum C-reactive protein (CRP) concentration of less than 6.5 mg/dL (low stress), and the second operation, preoperatively associated with sepsis or a major inflammatory insult, resulted in a peak CRP of more than 6.5 mg/dL (high stress). Data were paired so that each child served as his or her own control. The initial basal protein-calorie delivery was similar in both groups.

The mean peak CRP values were 14.1 +/- 10.7 mg/dL (high stress) and 4.1 +/- 2.3 mg/dL (low stress) and returned to normal levels earlier (before POD 8) after injury insult in the low-stress group. Analysis of energy expenditure on POD 2 demonstrated significantly elevated mean MEE values in the high-stress group (58.0 +/- 12.2 kcal/kg/d v 39.4 +/- 9.5 kcal/kg/d in the low-stress group; P = .0001). In contrast, analysis of POD 8 energy expenditure showed significantly lower mean MEE values in the high-stress group (50.7 +/- 12.0 kcal/kg/d) v (66.4 +/- 15.1 kcal/kg/d in the low-stress group; P = .0118) group.

The early (POD 2) hypermetabolic response to injury as determined by MEE effectively differentiated the two stress groups. This finding suggests that acute underlying illness is an important determinant of postoperative MEE. Furthermore, in the low-stress group, serial CRP levels returned to normal earlier, associated with significantly greater late (POD 8) MEE values. Because MEE is directly proportional to growth rate in healthy infants, and growth is retarded during acute metabolic stress, these findings suggest that increased energy is utilized for growth recovery following the earlier resolution of the acute injury response in the low-stress group. These data indicate that serial postoperative MEE can be used to stratify injury severity and may be an effective parameter to monitor the return of normal growth metabolism in surgical infants.