[Effect of metabolism-oriented substrate administration on energy and protein metabolism in polytraumatized...

An adequate "individually tailored" infusion and nutritional therapy is one of the essential prerequisites for an optimal healing process - especially in ventilated, polytraumatized patients with reduced compensatory capacities. There are nevertheless practically no publications dealing with the effect of substrate application adjusted to the measured metabolic rate on the energy and protein metabolism of the critically ill. In order to clarify this situation a prospective study was carried out on a group of 40 polytraumatized, ventilated patients, who were randomized into four groups, each receiving different infusion and nutritional regimen. The O2-consumption, energy expenditure, nitrogen balance and substrate concentrations in plasma and urine were determined, and the urea production rate and substrate turnover of all patients calculated. In the groups given nutritional support carbohydrate application adjusted to O2-consumption - lead to blood glucose concentrations which were persistently high. However, median values did not exceed 10 mmol/l and insulin application was never necessary. Energy expenditure - calculated from O2-consumption - averaged about 3000 kcal/day and was clearly below values previously reported in the literature for patients comparable to those studied in this investigation. There was no difference in energy expenditure between the patients treated with various infusion regimen. In none of the groups the median plasma urea concentration did exceed reference range. Despite an apparent improvement in nitrogen retention rate - through an increased amino-acid intake and a balanced energy input - an increased urea production rate resulted. When a balanced delivery of energy-yielding substrates is given, 2 g amino-acids/kg/day seems to be the upper limit of nitrogen support in the critically ill. 3-methylhistidine excretion in urine was parallel to urea production rate, indicating that the amino-acid sparing effect of carbohydrates is mainly derived from amino-acid conservation in muscle. These results seem to indicate that even in the early posttraumatic period a substrate application, adjusted to the measured turnover is possible without leading to a disturbance in homeostasis.