Minimum alveolar concentration of isoflurane in dogs administered two morphine doses

Concentração alveolar mínima do isoflurano em cães tratados com duas doses de morfina

ABSTRACT:

This study aimed to evaluate the effects of intramuscular 0.5mg kg^-1 (MOR_0.5) and 1.0mg kg^-1 (MOR_1.0) morphine premedication on the minimum alveolar concentration of isoflurane (ISO_MAC) in dogs. Eighteen client-owned female dogs were scheduled for elective ovariohysterectomy. Dogs received intramuscular MOR_0.5 or MOR_1.0 as premedication and propofol IV for induction of anesthesia. Isoflurane was delivered for maintenance of anesthesia and dogs were maintained under normocapnia and normothermia. Determinations of the ISO_MAC were conducted by use of the “up-and-down” method. Noxious stimulus (placement of Backhaus towel clamps, a midline skin incision and subcutaneous tissue dissection) was delivered approximately 50 minutes after premedication with MOR_0.5 or MOR_1.0. The calculated ISO_MAC was 0.98±0.15% in MOR_0.5 and 0.80±0.08% in MOR_1.0. The ISO_MAC was significantly lower in MOR_1.0 compared with MOR_0.5 (P=0.010). Results of this study suggested that intramuscular premedication with morphine 0.5 and 1.0mg kg^-1 decreases the ISO_MAC in a dose-related manner in dogs.

Key words:
autonomic response; canine; inhalational anesthetics; opioids