Metabolic pattern and lipid oxidation during abdominal surgery: midazolam versus propofol

Propofol is formulated in an emulsion similar to 10% Intralipid, and several authors have suggested that fat accumulates during its infusion. In this study we used indirect calorimetry to measure lipid metabolism during abdominal surgery in patients anesthetized with propofol, using midazolam as a control. Thirty patients were randomly divided into three groups: Group P (propofol 2 mg/kg + 5 mg.kg-1.h-1, n = 13); Group M (midazolam, n = 9), and Group I (midazolam + 10% Intralipid at rates similar to those infused in Group P, n = 8). They were monitored with an indirect calorimeter for 90 min. Data including oxygen consumption (VO2), CO2 production (VCO2), energy expenditure (EE), respiratory quotient (RQ), and lipid utilization were obtained every 15 min. VO2 increased in all groups at 45 min in respect to basal measurements with no differences between them. VCO2 decreased significantly only in Groups P and I, although no differences between the three groups were observed. EE did not vary in any of the groups. RQ decreased in all groups at 30 min, being significantly higher in Group M than in Groups P and I. Lipid oxidation increased in all groups from the beginning of the study reaching a plateau at 45 min. The lipid oxidation was higher in Groups P and I than in Group M, and coincided (80-100 g/24 h) with the amount of fat administered exogenously (85.4 g/ 24 h for a patient of 70 kg). Compared to VO2, VCO2, and EE, propofol behaves as other anesthetics. The fat administered in its formulation is metabolized in a preferential way, although it is likely that larger doses than those studied in our patients partially accumulate.