Effects of age and body composition on the metabolic responses to elective colon resection

Advancing age tends to be accompanied by predictable changes in organ-system function and body composition, as well as an increased prevalence of various diseases. Our knowledge of the metabolic responses to surgical stress is derived largely from studies of young and middle-aged individuals. Whether these responses are altered in the elderly is not well established; the characteristic changes in metabolic function and body composition that occur in the elderly may limit their ability to respond adequately and to survive severe or complicated surgical procedures. To evaluate the effects of age and differences in body composition on the metabolic responses to surgery, we studied 20 active and otherwise healthy men aged 43 to 77 years, before and after elective colon resection. Age was not related to weight or total body water (TBW) in the patients studied. Resting preoperative energy expenditure was strongly dependent on TBW (reflecting lean body mass) and age (r2 = 0.80, p less than 0.001), and to TBW and creatinine excretion (reflecting muscle mass) (r2 = 0.85, p less than 0.001). Energy expenditure increased 18 +/- 2% (range, 4% to 40%) after operation but this response was unrelated to age. Postoperative urine nitrogen was related to body weight or TBW, but not to age. Serum glucose, cortisol, white blood cell count count, and C-reactive protein responses were also independent of patient age. The metabolic responses of generally healthy men to a moderate surgical stress do not vary with age in the range studied. The metabolic responses to more severe or prolonged stress may be altered with advancing age and changes in body composition, and in patients with concomitant diseases.