The effect of acetate ringer solution, 6% hydroxyethyl starch saline and 20% mannitol solution on the serum concentration of propofol continuously infused

Changes in serum concentrations of propofol after administration of three different fluids were investigated in 42 scheduled surgical patients. Anesthesia was induced with propofol 2 mg.kg-1 and maintained with constant rate infusion of propofol 6 mg.kg-1.hr-1. After achieving a stable depth of anesthesia, 5 ml.kg-1 of acetate Ringer's solution, 6% hydroxyethyl starch saline solution or 20% mannitol solution was infused in 15 minutes. Blood samples each 2 ml were taken before and 0, 5, 15, 30 and 60 minutes after fluid treatment. We measured hemoglobin and hematocrit of the samples for calculating the dilution rate of the plasma with infusion treatment, and determined the serum concentration of propofol by HPLC-spectrofluorometry. After administration of each fluid, the serum concentrations of propofol decreased significantly to 17 +/- 15, 25 +/- 10 and 35 +/- 8%, respectively (mean +/- SEM). The dilution rate of the plasma from the fractional change in blood hemoglobin increased to 0.08 +/- 0.02, 0.24 +/- 0.03, and 0.36 +/- 0.03, respectively. Administration of mannitol might markedly increase distribution volume of propofol, and this can be attributed to osmotic action of mannitol and resultant expansion of extracellular fluid volume. The results of the present investigation suggest that this pharmacokinetic change decreased the concentration of propofol more significantly in mannitol treatment patients than in Ringer's solution or 6% hydroxyethyl starch saline treatment patients.