The Protein Equivalent of Nitrogen Appearance in Critically Ill Acute Renal Failure Patients Undergoing Continuous Renal Replacement Therapy

Objective

To assess the nutritional status of critically ill patients with acute renal failure on continuous renal replacement therapy (CRRT) and their protein needs by estimating the protein equivalent of nitrogen appearance (PNA).

Design

Prospective, observational study.

Setting

A 74-bed intensive care unit in a single tertiary care hospital.

Patients

Twenty-five consecutive critically ill patients with acute renal failure on CRRT.

Methods

The patients were studied over a period of 24 hours, at initiation on CRRT. The nutritional status was assessed by anthropometry and bioimpedance analysis. The PNA was estimated using the Bergstrom equation and PNA was normalized to body weight.

Results

The mean age was 58.2 ± 17 years and 20 (80%) were male. The mean weight was 67 ± 12 kg, body mass index was 25 ± 3.5 kg/m², and triceps and subscapular skin fold thickness were 13 ± 4.6 mm and 15 ± 2.5 mm, respectively. Bioimpedance studies showed that the total body water was increased at 61.7 ± 5.5% and body fat was 31.8 ± 5.4%. The PNA was 103 ± 35 g/day and normalized PNA was 1.57 ± 0.4 g/kg/day. The mean protein intake was 0.56 ± 0.38 g/kg/day, resulting in mean net negative protein balance of 1.0 ± 0.6 g/kg/day.

Conclusions

Malnutrition was uncommon in patients with acute renal failure at the time of initiation on CRRT, but their total body water was increased. They exhibited hypercatabolism and the mean normalized PNA was 1.57 g/kg/day. A large negative nitrogen balance was observed in them, since their protein intake was suboptimal.