Protein and energy tolerance by stressed geriatric patients.
Nutritional support of stressed geriatric patients remains empiric and has classically been limited by tolerance. Although the hypermetabolic response is known to increase protein and calorie demands, tolerance to increased loads of delivered nutrients in older patients has been questioned. We compared tolerance to nutrient delivery and nitrogen metabolism in 38 stressed surgical patients over age 65 to 38 Injury Severity Score or disease matched younger controls. Twenty-seven of the 31 geriatric patients (87%) who maintained normal renal function (serum creatinine less than 2.0 mg/dl) became azotemic (BUN greater than 30) while receiving 1.5 to 2.0 g of protein per kilogram of ideal body weight compared to only 21% of controls. This phenomenon led to inaccuracies in 17% of geriatric nitrogen balance studies because of unaccounted for serum accumulation of urea nitrogen (compared to only 6% in the control group). When calculated protein requirements were administered to the geriatric group, the mean nitrogen balance was -1.6. Resting energy expenditure as measured by indirect calorimetry demonstrated a strong correlation between actual calorie expenditures and calculated needs based on the Harris-Benedict basal energy expenditure (BEE) multiplied by an activity factor of 1.2 and a stress factor of 1.75 for trauma (r = 0.86, P less than 0.05) or 1.5 for general surgery patients (r = 0.72, P less than 0.05). In summary, energy requirements by stressed geriatric patients can be closely defined by calculation of the Harris-Benedict BEE in conjunction with appropriate activity and stress factors. However, attempts to deliver traditional levels of protein lead to azotemia and are frequently unsuccessful in achieving positive nitrogen balance.(ABSTRACT TRUNCATED AT 250 WORDS)