Evaluation of Cardiorespiratory Effects of Dexmedetomidine Isolated and Associated With Morphine in Bitches Submitted to Elective Ovariossalpingohisterectomy under General Inhalation Anesthesia

Abstract

Background: Elective ovariossalpingohysterectomy is one of the most accomplished surgeries in veterinary practice, presenting moderate degree of pain. Aiming at balanced anesthesia, α2-agonists have been increasingly used, with dexmedetomidine being characterized by its sympatholytic, sedative, analgesic properties and synergism with opioids, benzodiazepines and other drugs. The objective of this study was to evaluate the effects of dexmedetomidine alone and associated with morphine under the cardiovascular, respiratory and body temperature variables in the pre and trans-operative periods in bitches submitted to elective ovariossalpingohisterectomy under general inhalation anesthesia.

Materials, Methods & Results: Sixteen bitches were used in this study, which were submitted to elective ovariossalpingohisterectomy, all of which were clinically healthy based on clinical and hematological results. The animals were randomized into two groups, in which intramuscular dexmedetomidine alone and 5 µg/kg (DG) and 0.3 mg/kg morphine (GDM). In both groups, anesthesia was induced with propofol administered and maintained with isoflurane diluted in 100% oxygen administered through a calibrated vaporizer and appropriate anesthetic system based on the weight of the animal and kept under spontaneous ventilation. After stabilization of the patient, the surgical procedure started, which lasted 45 minutes. The parameters evaluated were heart rate (HR), respiratory rate (ƒ), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), body temperature (TºC), expired isoflurane concentration , partial carbon dioxide gas pressure (ETCO2) and oxygen saturation in hemoglobin (SatO2), which were measured before and after the application of preanesthetic medication and at specific surgical times: 5 and 15 min after anesthetic induction; during the incision of the skin; muscle incision; ligation of the left ovary; ligation of the right ovary; ligation of the uterine body; laparorrafia; suture and at the end of surgery. A significant difference was observed between the groups in respiratory rate, systolic blood pressure, body temperature, partial pressure of carbon dioxide, saturation of oxygen in hemoglobin and pH, only in some times evaluated. GDM bradycardia occurred 30 min after preanesthetic medication; acidemia and mild to moderate hypercapnia in both groups, being more pronounced in GDM, although without statistical difference, and hypothermia. The concentration of isoflurane expired in both groups was higher during the muscle incision until laparorrhaphy compared to the other surgical times.

Discussion: The results of this study show that there was adequate analgesia during the elective ovarian resection procedure, considering that the values found during the surgery were relatively lower than the baseline values and within the physiological limits for the species, even during the moments of greater painful stimulation, such as ligation of the ovaries and ligation of the uterine body. In the GDM group, bradycardia occurred after 30 min of pre-anesthetic medication, but its occurrence was transient and without interfering with blood pressure, increasing to the next evaluation time and stabilizing in physiological values for the species. There was also a gradual reduction in respiratory rate in both groups over time, with an increase in PaCO2 in GDM at the end of surgery, indicating respiratory depression, as well as a reduction in pH in both groups at all times.