Efeito da clonidina sobre a variabilidade da frequência cardíaca em cães anestesiados

Abstract

Clonidine is an alpha-2 adrenergic agonist with new potential application as a pre-anesthetic medication for a fear-based behavioral problem dogs, due to the attenuation on sympathetic nervous system effect. However, the risks associate to de cardiac autonomic and hemodynamic effects of clonidine, and its association with other drugs should be considered. In this context, the aim of this study was evaluate the effects of the pre-anesthetic use of clonidine (5μg.kg-1), on time domain heart rate variability, and arterial blood pressure in anesthetized healthy dogs. Six healthy mixed-breed, adult dogs were submitted to both clonidine (CLG) and placebo control (CG) anesthetic protocol, associated to propofol (8mg.kg-1), isoflurane (1CAM), tramadol bolus (2mg.kg-1), and continuous infused (1.5mg.kg-1.h). Time domain heart rate variability (HRV) and arterial blood pressure (systolic, mean, and diastolic) was evaluated along the time. All time domain HRV variables were higher on CLG (total time of anesthesia), especially when associated with tramadol bolus (T4), continuous infusion (T8), and on tracheal extubation time (T10). No important differences were observed on arterial blood pressure, but two dogs presented second-degree atrioventricular block (Mobitz II) in the tramadol bolus time (T4). Thus, clonidine increases the time domain HRV by sympathetic outflow block and rise on parasympathetic tonus, accentuated by the autonomic synergic effect of tramadol, resulting in cardiac electrical disturbance, which discourage this association (clonidine and tramadol) in anesthetic protocols for dogs with fear-based behavioral problems.