use of labetalol in controlled hypotension: experimental and clinical studies

ABSTRACT

The available drugs to attain controlled hypotension during anesthesia are not entirelysatisfactory. Tachycardia, tachyphylaxis and metabolic acidosis were encountered during their use. Labetalol hydrochloride [Trandate] was investigated as an adjunct to control hypotension experimentally in ten dogs as well as clinically in twenty patients.In dogs, labetalol in a bolus dose of 0.5, 1, 2 mg kg-1 produced dependant depressor and negative chronotropic effects.The urineoutput decreased with blood pressure drop and gradually increases to normal with the rise of blood pressure after stoppage of halothane.Labetalol 1 mg kg-1 injected intravenously in dogs at a rate of 0.2 mg kg-1 min-1was found to antagonize the pressor response induced by noradrenaline [2 and kg-1] and the depressor response induced by isoprenaline [1 and kg-1], but without any effect on the depressor response induced by acetylcholine [1 ug kg-1]. Clinically, intravenous injection of labetalol in a dose of 1mg kg-1 at a rate of 02 mg kg-1 min-1 in patients under different concentrations of halothane anesthesia resulted in astatistically significant drop in the mean arterial blood pressure [MAP] and heart rate 10-25 minutes after injection. This drop in the MAP was found to be25.49%,27.76% and 34.72% using 1. 1.5 and 2% halothane concentration, respectively. The mean change in the central venous pressure was found to be statistically insignificant. The mean value of heart rate dropped by 2.67%, 1.75% and 12.15% using 1, 1.5 and 2% halothane concentration, this change was found to be statistically significant. No changes in pH, PaCO2 or PaO2were found at any concentration of halothane. The use of 1.5% halothane concentration showed no significant changes in all indices from that resulted at 1% concentration of halothane