Protein catabolic rate in patients with acute renal failure on continuous arteriovenous hemofiltration and total parenteral nutrition

Abstract

Continuous arteriovenous hemofiltration (CAVH) has been used to provide nutrition support to critically ill patients in acute renal failure (ARF). Limited information exists regarding protein needs of these patients. Nineteen postoperative patients in ARF and on CAVH and total parenteral nutrition (TPN) were studied (10 men; 9 women; mean age, 65 yr) to determine protein needs (protein catabolic rate; PCR), urea nitrogen appearance (UNA), and total nitrogen appearance (TNA). TPN was adjusted to meet the needs estimated by the Harris-Benedict and Long equations. A total of 38 24-h studies were conducted on the 19 subjects. TNA, UNA, and PCR were determined by direct measurement of body losses and calculation of body pool nitrogen changes. Patients received an average of 93.9 ± 30.5 g of protein (1.4 g/kg) and 2,600 ± 534 kcal/day in TPN. Mean PCR was 117.5 ± 42.8 g/day; UNA was 18.3 ± 6.9 g/day. TNA and UNA were strongly correlated (r= 0.99; P< 0.001). PCR was less strongly correlated with estimated protein needs (r= 0.35; P = 0.03). A regression equation was developed describing the relationship between TNA and UNA as follows: TNA = 1.895 + 0.9444 (UNA) or UNA = 0.1602 (PCR) - 0.916. On the basis of this study, CAVH permits the provision of adequate nutrition support to critically ill, unstable patients. It appears that the protein needs of patients in ARF on CAVH can be accurately estimated by determining UNA through the measurement of urea losses and urea body pool changes and by regression equations to calculate PCR. Because of the complexity of the collection process, it may still be advantageous to estimate needs by standard nutritional assessment equations.