Nitrogen balance in extremely low birth weight infants with nonoliguric hyperkalemia.

We measured nitrogen balance and urinary 3-methylhistidine molar ratios in 33 extremely low birth weight infants (12 with hyperkalemia and 21 without) for the first 3 days of life. Although all infants were in negative nitrogen balance during the study, there was no difference in the degree of negative nitrogen balance between the two groups. There was also no difference in the 3-methylhistidine/creatinine molar ratios, indicating that muscle protein catabolism did not differ. We conclude that it is unlikely that catabolism contributes to the development of nonoliguric hyperkalemia in extremely low birth weight infants.