Relationship between nitrogen loss and blood urea nitrogen concentrations in patients requiring continuous renal replacement therapy

Aim It is well known that continuous renal replacement therapy (CRRT) produces some amount of nitrogen loss, but there are few tools that are easily applied to measure it. This study aimed to evaluate nitrogen loss using blood urea nitrogen (BUN) measurement in patients receiving CRRT. Methods The subjects were 28 patients who received CRRT (except for liver failure) between 2010 and 2012. Nutrition data and nitrogen excretion in dialysate and urine were measured. Results The median age of the patients was 61 years, with an Acute Physiology and Chronic Health Evaluation score of 27 points and a Sequential Organ Failure Assessment score of 12 points. All-cause hospital mortality was 50%. Median protein intake was 40 g/day. The daily urinary volume was 245 mL and volume of dialysate was 26,000 mL/day. The median amount of nitrogen loss was 10.58 g/day, with BUN showing a strong correlation (r = 0.804, P < 0.0001). There was a poor relation between protein intake (g/kg body weight) and nitrogen balance (r = 0.322, P = 0.002). Conclusions In patients receiving CRRT, the nitrogen loss showed a positive correlation with BUN but not with protein intake. According to the guidelines, recommended protein intake was 1.5-2.0 g/kg/day, but we should be careful to avoid elevating BUN at the same time. The results showed that BUN might be a useful marker to check nitrogen balance in the nutritional management of patients receiving CRRT.