Kinetic of body nitrogen loss during a whole day infusion and withdrawal of glucose and insulin in injured patients

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Abstract
To investigate the kinetics of body nitrogen (N) excretion during 24 h glucose infusion (relating glycemia with insulin supply) and during subsequent 24 h saline infusion in injured patients during a full blown stress reaction. To define the lag time between the start or the withdrawal of glucose and insulin infusion, and the modification in the N loss from the body, and the time span to reach the maximum effect and its size. The knowledge of these variables is mandatory to plan short term studies in critically ill patients, while assuring the stability of the metabolic condition during the study period, and also to assess the possible weaning of the effect on protein breakdown during prolonged glucose and insulin infusion. 24–36 h after injury, patients were fasted (2<0.4). Excluded patients were those with abnormal nutritional status, cardiovascular compromise and organ failures. Patients showed a 33% increase in measured versus predicted fasting EPR and a consistent increase in N and 3-MH urinary loss. An infusion of glucose at 5.95±0.53 mg/kg·min (97.20±0.03% of the fasting measured EPR) with 1.22±0.18 mU/kg·min insulin infusion reduced N and 3-MH loss after a time lag of 12 h. The peak decrease in body N (−36%) and 3-MH loss (−38%) was reached during the first 12 h of glucose withdrawal period. Thereafter, during the following 12 h, the effect completely vanished confirming that it is therapy-dependent and that the metabolic environment of the patients did not change during the three days study period. 24 h glucose withdrawal reduces N and 3-MH loss in injured patients, the drug-like effect is maintained during the first 12 h of withdrawal and thereafter disappears. The study suggests that at least a 24 h study period is necessary when planning studies exploring energy-protein metabolism relationship in injured patients, and, again 24 h before changing protocol in a crossover study.