Clinical relevancy of nonurinary nitrogen excretion in newborns and infants after digestive tract surgery.

Abstract

Whether the contribution of nonurinary nitrogen excretion (N2nu) to total nitrogen excretion (N2tot) is clinically relevant has not been tested in children in an intensive care unit. Particularly after digestive tract surgery, fecal nitrogen losses, and losses via nasogastric tubes, enterostomies and wound drains may be large. We prospectively measured urinary nitrogen excretion (N2u) and N2nu 4 to 6 days after digestive tract surgery in 78 newborns and infants who were given total parenteral nutrition. Two hundred seven collections of excreta, each representing one 24-hour period, were obtained. Median N2nu was 15 mg/kg/24 hours (range, 0.4-153), median N2u 153 mg/kg/24 hours (range, 57-558), median N2tot 179 mg/kg/24 hours (range, 72-577), and the median ratio of N2nu and N2u 9.9% (range, 0.2-110). The observed variations could not be attributed to differences in the severity of the underlying disease or the surgical stress. The mean difference between N2tot and N2u was 21 mg/kg/24 hours (95% prediction interval -20 to +63). Use of a linear regression equation that predicts N2tot according to N2u and the weights of other excreta eliminated bias and improved precision (95% prediction interval -34 to +34 mg/kg/24 hours). For individual measurements, however, considerable imprecision remained. In newborns and infants, receiving parenteral nutrition 4 to 6 days after digestive tract surgery, N2nu is variable and not to be neglected. The only way to accurately assess N2tot in individual patients is by measuring the nitrogen content of all excreta.