CARDIOVASCULAR EFFECTS AFTER EPIDURAL INJECTION OF XYLAZINE IN ISOFLURANE-ANESTHETIZED DOGS

The cardiovascular effects following epidural injection of xylazine or isotonic saline during isoflurane anesthesia were assessed in six hea lthy dogs. Dogs were anesthetized with isoflurane in O-2 and maintaine d at 2.0% end-tidal concentration. Ventilation was controlled to maint ain PaCO2 at 35 to 45 mm Hg. The dorsal pedal artery was cannulated fo r measurement of arterial blood pressure (AP)(systolic AP, mean AP, di astolic AP) and for blood sample collection. Arterial pH and blood gas tensions (PaO2 and PaCO2) were determined. Cardiac output was measure d by thermodilution. The electrocardiogram (ECG), heart rate (HR), cor e body temperature, central venous pressure (CVP), mean pulmonary AP, and end-tidal isoflurane concentration (ETISO) and CO2 tension (ETCO(2 )) were monitored. Systemic vascular resistance (SVR), arterial HCO2 c oncentration, base balance, and cardiac index (Ct) were calculated. Af ter baseline measurements were taken, either xylazine (0.2 mg/kg) in 5 mt isotonic saline or 5 mt of isotonic saline was injected into the l umbosacral epidural space. Data were then recorded at 5, 15, 30, 45, 6 0, 75, 90, 105, and 120 minutes after epidural injection. Data were an alyzed by two-way analysis of variance (ANOVA) for repeated measures. When significant differences were encountered, mean values were compar ed using Bonferroni's test. The level of significance was set at P<.05 . Mean values for diastolic AP decreased at 90 and 120 minutes compare d with the mean value at 15 minutes after epidural injection of xylazi ne. No differences were detected at any time or between treatments for HR, systolic AP, mean AP, CVP, CI, SVR, mean pulmonary AP, temperatur e, ETCO(2), ETISO, arterial pH, PaCO2, PaO2, plasma bicarbonate concen tration, or base balance. Results of this study indicate that epidural injection of xylazine (0.2 mg/kg) is associated with minimal cardiova scular side effects during isoflurane anesthesia in mechanically venti lated dogs. (C)Copyright 1995 by The American College of Veterinary Su rgeons