Effect of anesthetic induction agents on cardiovascular neuroregulation in dogs.

The goal of this study was to examine the hypothesis that intravenous anesthetic induction agents alter neuroregulation of the cardiovascular system. Additional goals were to investigate this in an animal model devoid of other drug effects. Healthy mongrel dogs had arterial catheters inserted and pneumatic occluders positioned around the thoracic aorta and inferior vena cava. After 10 to 14 days of recovery, neurocirculatory control mechanisms were assessed in the absence of anesthesia by recording changes in the RR interval of the electrocardiogram in response to alterations in systolic arterial pressure. Systolic pressure was manipulated over a range of 65 to 200 mm Hg by random occlusion of either the inferior vena cava (hypotension) or aortic (hypertension) occluders. The animals were then given bolus doses of either thiopental (20 mg/kg), diazepam (2 mg/kg), ketamine (5 mg/kg), or etomidate (1.2 mg/kg) on separate days and in random order. The arterial pressure alterations were repeated 3, 10, and 20 minutes after the drugs were given. Regression curves were calculated expressing the slope relation between RR interval and systolic pressure at awake control and each time point after drug administration. The responses were compared with control by repeat measures analysis of variance. Thiopental significantly decreased this slope relation for 10 minutes. Diazepam decreased this slope at 3 minutes only. Ketamine, like thiopental, decreased this slope for 10 minutes. Following etomidate, the slopes were similar to control. We conclude that thiopental, diazepam, and ketamine impair neurocirculatory control capabilities. The effect of diazepam is only transient, whereas that of thiopental and ketamine is longer, and etomidate does not affect these reflexes.