The association of propofol and opioids grants analgesia to the anesthetic protocol, allowing the development of a surgical procedure. Despite there are several researches concerning the pharmacological interactions of propofol and opioids, data still lacks regarding doses and effects when such agents are infused in association in dogs. Therefore, it was proposed an evaluation of the hypnoanalgesia potential promoted by a continuous infusion of propofol and sufentanil in dogs.

For such, it was used twelve adult female mongrel healthy dogs, with mean weight of 18.21 ± 2.81 kg. Dogs were given propofol (5 mg/kg IV) following premedication with acepromazine (0.05 mg/kg IV). Anesthetic maintenance was done with propofol, which was infused continuously at 0.2 mg/kg/minute, associated to sufentanil in three different doses: (A) 0.25 µg/kg/minute; (B) 0.5 µg/kg/minute; and (C) 0.75 µg/kg/minute. Each dog underwent all three doses of sufentanil, with a one-week interval between procedures. It was evaluated the degree of analgesia; muscle relaxation and palpebral reflex. Such parameters were assessed from induction until 120 minutes of anesthesia, each 15 minutes.

When dose (A) was infused, 9 animals showed no response to nociceptive stimuli after 90 minutes of anesthesia; when dose (B) was infused, 11 dogs had no response to painful stimuli after 45 minutes of anesthesia. On the other hand, none of the animals showed response to nociceptive stimuli after 30 minutes of anesthesia when dose (C) was used. It was also seen that when dose (A) was used, 72.2% of dogs had positive palpebral reflex during the experiment. For dose (B), only 33.3% of dogs had positive palpebral reflex, while for dose (C), such reflex was abolished in 100% of the animals during the whole period of anesthesia. Regarding muscle relaxation, it was seen a deep relaxation during the whole experiment, independently of the dose that was infused. Statistical analysis by Fisher's exact test showed differences between doses from 15 to 60 minutes of anesthesia (P=0.0048 to P=0.0243). Anyway, it was seen that the highest the infused dose, the greater the number of animals that showed negative nociceptive responses. For muscle relaxation, there was no differences between doses, while for palpebral reflex, differences existed between groups (P=0.0006).

Results allowed concluding that the degree of analgesia promoted by sufentanil is settled faster when the highest dose is infused. Moreover, using the highest dose, one can assume that a surgical procedure can be safely performed after 30 minutes of infusion. However, a previous bolus injection of sufentanil can decrease this period, in which analgesia degree was not considered sufficient to make feasible a surgery.