THE INFLUENCE OF THE BOLUS INJECTION RATE OF PROPOFOL ON ITS CARDIOVASCULAR EFFECTS AND PEAK BLOOD-CONCENTRATIONS IN SHEEP

The influence of the bolus injection rate of propofol on its cardiovas cular effects has not been extensively studied. We therefore examined the influence of the injection rate of IV bolus doses of propofol on i ts acute cardiovascular effects and peak blood concentrations in seven chronically instrumented sheep. Each received IV propofol (200 mg) ov er 2 min (slow injection) and 0.5 min (rapid injection) on separate oc casions in random order. The rapid injection was associated with more profound decreases in mean arterial blood pressure than slow injection (35.7% vs 23.7% maximal reductions from baseline, respectively; P = 0 .02). There were no significant differences between the injection rate s for peak reductions in myocardial contractility, increases in heart rate, or degree of respiratory depression. Concurrently, the rapid inj ections were associated with significantly higher arterial (26.9 vs 11 .9 mg/L) propofol concentrations in a manner consistent with indicator dilution principles. There were no differences in the peak coronary s inus concentrations between the injection rates. We conclude that the rapid injection of propofol in the context of the induction of anesthe sia produced significantly higher peak arterial propofol concentration s and suggest that it is these higher concentrations that produced rel atively greater reductions in arterial blood pressure from rapid injec tions. Implications: Propofol is injected into a vein to initiate anes thesia. It can cause a rapid decrease in blood pressure, which may be dangerous to the patient. We examined the effect of rapid and slow inj ection rates of propofol in sheep and found that rapid injection cause d a greater decrease in blood pressure. This was because rapid injecti on caused higher concentrations of propofol in the blood immediately a fter the injection. We believe that if the same processes occur in hum ans, there may be little advantage in injecting propofol rapidly.