Venodilation Contributes to Propofol-Mediated Hypotension in Humans

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Abstract
The present investigation explored the possibility that the commonly observed hypotension that occurs during induction of anesthesia with propofol might be related to its ability to produce venodilation. Thirty-six ASA I and II patients who received no premedication were studied. The first 20 patients were divided into two equal groups. Hemodynamic measurements consisted of heart rate, arterial blood pressure, and forearm venous compliance by occlusive plethysmography. Baseline measurements were made in awake patients while resting in a supine position. Repeat measurements were made during steady-state infusions of propofol (2.5 mg/kg bolus injection, followed by a continuous infusion at 200 micrograms.kg-1.min-1) or thiopental (4 mg/kg bolus injection, followed by continuous infusion at 200 micrograms.kg-1.min-1), 10 min after tracheal intubation while patients were artificially ventilated. Both anesthetics resulted in a significant (P less than 0.05) and similar tachycardia; however, propofol produced significant decreases in systolic (-30 +/- 9 mm Hg) and diastolic (-11 +/- 4 mm Hg) arterial blood pressure. Forearm venous compliance was significantly increased during propofol administration but unchanged in patients receiving thiopental. In four additional patients receiving smaller consecutive infusions of propofol (50 and 100 micrograms.kg-1.min-1), significant subtle increases in forearm compliance were also recorded. These increases were not observed in four patients who received placebo infusions. Thus, one mechanism promoting hypotension during propofol anesthesia in humans seems to be related to its direct effects on venous smooth muscle tone and presumably venous return.

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