OXYGEN-UPTAKE AND CARBON-DIOXIDE PRODUCTI ON IN ABDOMINAL AORTIC RECONSTRUCTION

Oxygen uptake (VO2) and carbon dioxide elimination (VCO2) can be measu red with an indirect calorimeter; this method is well established in r outine monitoring of ICU patients to evaluate metabolic state as a ref lection of stress. In various experimental studies it was demonstrated that anaesthetics can influence whole-body metabolism. The purpose of this study was to examine whether indirect calorimetry can be used in traoperatively during routine anaesthesia and whether presumable chang es in metabolism can be detected immediately. Abdominal aortic cross-c lamping changes circulation, nutritional supply of the lower extremiti es and thus VO2 and VCO2. We therefore used this operation for our stu dy. Method. Eleven patients, mean age 64 years, undergoing reconstruct ion of the aortic bifurcation, were studied. After premedication with piritramid and atropine, total intravenous anaesthesia (TIVA) was per- formed with fentanyl and midazolam after an induction with thiopental. Patients were ventilated with a Servo-Ventilator 900 D and a constant FiO2 of 0.5, without N2O. Routine monitoring consisted of ECG, pulsox imetry, CVP and continuous AP. VO2 and VCO2 were measured with a Delta trac(R) (Datex), and data were registered every minute. For statistica l evaluation we used a Wilcoxon-Ranksum test for matched pairs, p < 0. 05 was considered significant. Data from specific time (5 min after in tubation, 5 min before clamping; 5, 10 and 15 min after clamping, befo re declamping and 5 and 10 min after declamping and at the end of surg ery) were calculated. In addition to absolute values, we compared the measured VO2 and VCO2 to baseline (5 min before clamping = MP2). Resul ts. Mean operating time was 139 min+/-37; aortic cross-clamping time f or the first extremity was 38 min and 55 min for the second. As expect ed, there was a significant decrease in VO2 (90% of baseline) and VCO2 (75% of baseline) during aortic cross-clamping. After declamping VO2 again rose to 110% of baseline, or to 103% for the second limb. VCO2 i ncreased to only 90% and 82%, respectively. At the end of surgery VO2 reached baseline, whereas VCO2 remains at 83%. The respiratory quotien t VCO2: VO2 was markedly reduced from 0.95+/-0.156 to 0.73+/-0.06 duri ng surgery. The Deltatrac(R) showed every change in VO2 without delay; changes in VCO2 seem to occur somewhat retarded. Discussion. Aortic c ross-clamping leads to a marked decrease in VO2 and VCO2 reflecting th e temporary reduction in whole-body metabolism. Declamping results in a compensatory rise, especially in VO2. VCO2 seems to increase less af ter declamping, perhaps due to the CO2 pool of the organism or to a ch ange in metabolism from carbohydrate to mainly fat oxidation. The resu lts of this study demonstrate that indirect calorimetry can easily be performed during anaesthesia and surgery. Preconditions are a non-rebr eathing system without airleak, constant FiO(2) < 0.6 and no use of ni trous oxide.