Cardiorespiratory and electrocardiographic effects of methadone or morphine in the perioperative period in anesthetized dogs with continuous rate infusion of propofol and submitted to ovariohysterectomy

Abstract

The aims of this study were compare the electrocardiogram (ECG) and cardiopulmonary effects of methadone or morphine, both injected intravenously (IV) in dogs anesthetized with continuous infusion of propofol. Sixteen healthy female mongrel dogs were used in this study for elective ovariohysterectomy. The animals were allocated in random order into two groups assigned GME (methadone 0.3 mg kg-1, IV) or GMO (morphine 0.3 mg kg-1, IV). Parameters were evaluated: heart rate (HR), P-wave amplitude (Ps and PmV), interval between Ps and R waves (PR), QRS duration (QRS), R-wave amplitude (R), duration the interval between the Q and T waves (QT), systolic blood pressure (SBP), rectal temperature (RT), respiratory rate (RR), end tidal of carbon dioxide (ETCO2) and periferic oxyhemoglobin saturation (SpO2). Postoperative analgesia was assessed by mechanical nociceptive stimulus based on the scale proposed by Firth and Haldane (1999) and rescue analgesia based on the visual analogue scale. HR was lower in GME in relation to GMO. The P, PmV, PR, QRS, R and QT values remained within their normality tracks, showing no clinical importance. Apnea and ETCO2 increased in both groups. There was no difference between groups of the analgesic effects. It can be concluded that methadone and morphine promote similar cardiovascular effects after IV injection during surgery in dogs anesthetized with propofol by continuous rate infusion, however, when methadone used, assisted ventilation is required. In addition, both drugs promote postoperative analgesia until six hours.