[Metabolic models for the interpretation of indirect caloric measurements in intensive care patients].

Precondition for the evaluation of indirect calorimetry data by standard procedures is an undisturbed physiological metabolic situation. Metabolic changes in stress metabolism, which are a reduction of enzyme activity, increased rates of gluconeogenesis und ketogenesis, and simultaneous occurrence of lipolysis and lipogenesis cannot be considered by those calculations. Various problems concerning the evaluation of data obtained on traumatized patients confirm the presumption that standard procedures are not suitable in the case of posttraumatic metabolic disturbances. Therefore, we developed two computer-supported metabolic models, which assume a reduced activity of the three key enzymes: pyruvate dehydrogenase (PDH), phosphofructokinase (PFK) and citrate synthetase (CS). The blocked metabolites are bypassed to gluconeogenesis, lipogenesis and in so called 'pools' ('glucose-pool', 'acetyl-pool'). In addition, a detailed simulation of amino acid degradation is permitted. The models were applied to evaluate indirect calorimetric data of four patients, which could not be evaluated by standard procedures. It was shown that an evaluation of all data was possible by at least one model. All enzymes presented a slight to complete blockade. The calculated maximal activities of PFK was 1.59 mol/d, of PDH 6.31 mol/d and that of CS 6.55 mol/d. These activities were far below the values of normal human beings. As a result of these enzyme inhibitions, high rates of gluconeogenesis (max. 387 g/d) and lipogenesis (max. 511 g/d) as well as high values for the glucose-pool (max. 387 g/d) and the acetyl-pool (max. 641 g/d) were calculated. The interpretation of the pools was difficult. Renal elimination of the metabolites was not found in our patients, an accumulation was impossible for osmotic reasons. Therefore, despite the catabolic hormonal character of stress metabolism, storage as molecules of high molecular weight should be taken into account.