[Pharmacokinetics of propofol injected after deliberate preoperative hemodilution]

The effects of acute isovolaemic haemodilution (AIH) on propofol pharmacokinetics were studied in 16 male patients scheduled for prostatectomy. They were all ranked ASA 1, and were randomly allocated to two groups, group I (n = 8), who did not undergo any haemodilution, and group II (n = 8), in whom AIH was carried out. Anaesthesia was induced with a single 2.5 mg.kg-1 propofol bolus given in 30 s; maintenance was achieved with fentanyl 2 micrograms.kg-1, atracurium 1 mg.kg-1, and a ventilation with a mixture of nitrous oxide in oxygen 50 %, with enflurane 1 %. Those patients due to be haemodiluted had blood withdrawn before surgery (1,387.5 +/- 423.3 ml), at the same time as they were given the same volume of modified fluid gelatin (Plasmion). The volume of blood to be withdrawn was calculated according to the initial haematocrit, and that required. Haematocrit was decreased to 32.3 +/- 3.9 % (extremes 27 and 37 %). Thereafter blood samples were then collected over a 24 h period, which included surgery. Propofol was assayed in whole blood using high performance liquid chromatography. Analysis with a three-compartment model was carried out. The AIH only altered the central compartment volume (65.5 +/- 15.6 l in the control group vs 83.6 +/- 13.3 l in group II, p less than 0.01). Initial concentrations were not significantly different in the two groups (2,892 +/- 762 ng.ml-1 in controls vs 2,373 +/- 589 ng.ml-1 in the others). Clinically, anaesthesia and recovery were uneventful. It is concluded that the induction dose of propofol in patients scheduled for haemodilution does not require any alteration.