Abstract
Hemodialysis results in significant amino acid and protein losses and increases the patient's need for, and tolerance to, standard doses of protein. Since urea accumulation increases proportionately with increasing doses of protein in patients with normal renal function, urea accumulation may result when protein intake is increased to offset losses occurring in the dialysate. As a consequence, an increased requirement for dialysis may occur that might be poorly tolerated by the critically ill patient. This study was designed to determine the relationship between nitrogen intake and urea appearance in five patients requiring hemodialysis and total parenteral nutrition.
Daily caloric and nitrogen intakes were determined. Urea appearance was calculated from measures of urine urea nitrogen excretion and daily body urea accumulation. Results of 108 measurements in treatment courses ranging from 23–79 days found that the average caloric intake (1984 ± 55 calories/d) and nitrogen intake (11.0 ±0.4 g/d) resulted in a positive nitrogen balance (0.8±0.4 g/d) and a urea appearance rate of 9.4±0.8 g/d. Nitrogen intake correlated both with urea appearance (r = 0.59, p<0.001) and nitrogen balance (r = 0.49, p<0.001). Positive nitrogen balance was associated with improvements in measures of total iron binding capacity (p<0.05).
Nitrogen intake directly relates to urea appearance, and positive nitrogen balance can be achieved without increasing dialysis requirements. In this group of patients, 28.3 calories per kg ideal body weight and 0.8 g of protein per kg ideal body weight were required to achieve nitrogen equilibrium.
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