CARDIOVASCULAR EFFECTS OF EPIDURALLY ADMINISTERED MORPHINE AND A XYLAZINE-MORPHINE COMBINATION IN ISOFLURANE-ANESTHETIZED DOGS

Cardiovascular effects of epidurally administered morphine, a morphine -xylazine combination, and saline solution (control) during isoflurane -maintained anesthesia were assessed in 6 healthy dogs. Anesthesia was induced with isoflurane in O-2 and was maintained at 2.0% end-tidal i soflurane concentration. Ventilation was controlled to maintain PaCO2 at 35 to 45 mm of Hg. The dorsal pedal artery was cannulated for measu rement of systolic, mean, and diastolic pressures, and for blood sampl e collection. Arterial blood pH and gas tensions were determined every 30 minutes. Cardiac output was determined by thermodilution. The EGG, heart rate, body temperature, central venous pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, end-tidal isoflu rane concentration, and CO2 tension were monitored. Systemic and pulmo nary vascular resistance, arterial HCO3- concentration, base excess, a nd cardiac index were calculated. After baseline measurements were tak en, morphine (0.1 mg/kg of body weight) in 5 mi of isotonic saline sol ution, morphine and xylazine (0.1 mg of morphine and 0.02 mg of xylazi ne/kg) in 5 mi of isotonic saline solution, or 5 mi of isotonic saline solution was injected into the lumbosacral epidural space. Data were recorded at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after epid ural injection. Statistical analysis included ANOVA for repeated measu res. Significance was set at P < 0.05. None of the measured variables was significantly different among the 3 treatments at any time. Result s of the study indicated that epidural administration of morphine or m orphine and xylazine is not associated with significant cardiovascular side effects during isoflurane-maintained anesthesia in dogs.