[Postoperative nitrogen loss].

Total nitrogen excretion was studied prospectively in 54 surgical patients during the first and second postoperative day by the Chemiluminescence method. The results were compared to three different methods for approximation of the total nitrogen excretion. Daily total nitrogen excretion was 13.13 +/- 5.7 g after peripheral vascular procedures, 15.97 +/- 8.1 g after major surgical procedures and 20.42 +/- 5.2 g in septic patients. The assessment of total nitrogen excretion by the three other methods underestimated real nitrogen losses by 20-52%. The nitrogen concentration in various secretions was relatively constant. We conclude that measuring the urine nitrogen losses only and adjusting them for the calculation of the total nitrogen excretion by several factors in incorrect. Direct measurement of total nitrogen excretion is too costly for the use in daily clinical practice.