[Indirect calorimetry in the artificially respirated polytraumatized patient. I. Studies in adults]

Significant changes in oxygen uptake (VO2) and carbon dioxide output (VCO2) as well as resting energy expenditure (RMR) can be observed in critically ill patients. Reliable data, although needed by the clinician especially in long term ventilated patients, have not been obtainable so far. We developed a modular system which provides by means of mass-spectrometry, accurate reproducible results. Furthermore, the design of the gas sampling module minimalizes systemical failures in the expiratory branch. Two groups of polytraumatized patients (n = 10, n = 7 respectively) with different amounts of intravenous amino-acid support and identical energy supply were included in the study. During the first week all patients showed significantly elevated values for VO2 and VCO2 with a tendancy to increase. High amino-acid supply resulted in higher rate of gas exchange and disproportional increase in energy expenditure. Subsequently reduced carbohydrate intake was found to be effective in reduction of gas exchange earliest after 24 h. Oxidation rates for glucose and fat did not correspond to energy supply ratio of substrates. It can be stated that in polytraumatized patients amino-acid supply more than 75 g/24 h/m2 is not economical in terms of energy gains and is therefore not generally recommended. Reduction of carbohydrates in the weaning period of respirator in these patients is likely to be effective only in borderline cases and started early before weaning (greater than 24 h). Energy supply by means of carbohydrates should exceed the energy derived from fat supply in the nutritional regime according to oxidation rates in polytraumatized patients.