Male and female sterilization have been established as the main technique to reduce the huge number of mongrel dogs. However, there are several barriers regarding to the choice of the best anesthetic protocol, in terms of efficacy, security and cost reduction. The aim of this study was to evaluate the analgesic, cardiorespiratory and hemogasometric effects of epidural anesthesia with a large volume of lidocaine in combination with morphine in female dogs submitted to ovariosalpingohisterectomy (OSH), with or without oxygen supplementation. Twelve adult female dogs were used, with average weight of 11.5 +/- 3.7kg and age of 1 to 4 years. The animals received acepromazine (0.1mg kg(-1)) and meperidine (5mg kg(-1)) as premedication, administered by the intramuscular route. Fifteen minutes later, thiopental (10mg kg(-1)) was administered by intravenous route, followed by endotracheal intubation. The animals were allocated into two groups: GCO (group with oxygen, n = 06), where the animals received 100% oxygen supplementation and GSO (group without oxygen supplementation, n = 6), mantained with endotracheal intubation, but without oxygen supplementation. After intubation, epidural with morphine (0,1mg kg(-1)), adjusted to 1mL 3kg(-1) in lidocaine 2% without epinepherine was administered. Immediately after epidural administration, the animals were positioned in dorsal recumbency, with the head in the same level of the body. In both groups, surgery was performed without the need of additional analgesia and without signs of pain. Mean arterial pressure (MAP) was lower in GSO in all moments compared to baseline values. In GCO, MAP was lower after premedication and epidural anesthesia. Respiratory rate was lower from M1 to M6 in GSO. The SaO(2) and PaO2 were higher in GCO when compared to GSO. The pH was lower in GCO after 15 minutes after premedication, until 40 minutes after the epidural administration, compared to GSO. It was concluded that the epidural administration using morphine and lidocaine in the dosage and volume proposed are effective to OSH procedure in dogs. The lack of oxygen supplementation promoted minimal cardiovascular and hemogasometric alterations, which is feasible in sterilizations campaigns where there is no possibility of oxygen supplementation of the animals.
