Meperidine-acepromazine-pentobarbital anesthesia in cats: reversal by 4-aminopyridine and yohimbine.

Groups of atropinized cats (6/group) were given IM meperidine (5.5 mg/kg of body weight) plus acepromazine (0.25 mg/kg). Forty minutes later, the cats were anesthetized to disappearance of pedal reflexes with 1% pentobarbital IV. Volume of anesthetic was recorded. Five minutes later, the cats were given IV saline solution (2 ml; control group), the antagonists 4-aminopyridine (4-AP; 0.5 mg/kg), yohimbine (0.4 mg/kg), or a combination of 0.5 mg of 4-AP/kg plus 0.4 mg of yohimbine/kg. Mean arousal time (MAT), walk time (MWT), respiratory rate, and heart rate were measured. Emergence phenomena also were recorded. Meperidine plus acepromazine caused mydriasis and mild sedation without ataxia or marked protrusion of the 3rd eyelid. The cats did not resist restraint for venipuncture. The pooled mean dosage level of pentobarbital required for anesthesia was 12.3 mg/kg. Control group MAT and MWT were 66.2 minutes and 126 minutes, respectively. Marked residual sedation lasted several hours. In cats given 4-AP plus yohimbine, MAT and MWT were decreased to 4.4 minutes and 36.5 minutes, respectively. These values were not significantly shorter than those same values in cats given 4-AP or yohimbine alone (P greater than 0.05), but the combination of 4-AP plus yohimbine produced a qualitatively better reversal of anesthesia than did 4-AP or yohimbine alone. Emergence was smooth in all 4 groups; mild-to-moderate residual sedation lasted 2 to 4 hours in the principals. Relapses, drug side effects, and behavioral aberrations were not observed. Mean respiratory rates and heart rates decreased during anesthesia but these values were not excessively depressed or stimulated at any time. Cardiac irregularities were not detected by palpation or auscultation.(ABSTRACT TRUNCATED AT 250 WORDS)