Abstract

General anesthesia in phocids is potentially more complicated than other mammals due to their anatomical and physiological adaptations to diving. The objective of this project was to assess the benefit of premedication with midazolam for short duration procedures requiring endotracheal intubation in harp seals (Phoca groenlandica). Weaned female harp seals (n = 14; wt: 24.4 to 41.5 kg; age from 3.5 to 11 wks) were used for this study. The seals were housed in indoor tanks at the Maurice-Lamontagne Institute. A prospective, cross-over, blinded protocol was prepared to assess the effects of two doses of midazolam on induction, intubation and recovery parameters. Each animal was anesthetized three times, two weeks apart, and given either midazolam high dose (0.2 mg/kg), low dose (0.1 mg/kg) or saline control as pre-anesthetic medication intramuscularly. Mask induction of anesthesia with isoflurane at a vaporizer setting of 4% followed. Intermittent positive pressure ventilation (IPPV) was instituted manually following endotracheal intubation and various cardiovascular and respiratory parameters were monitored. Isoflurane was discontinued after the completion of the procedure (bronchoalveolar lavage). Weaning from IPPV involved stopping ventilation for one minute periods until the animal began spontaneous ventilation or was extubated. Extubation followed return to spontaneous ventilation or when it was believed that breath holding was occurring following adequate recovery from anesthesia. The quality of the induction, intubation, anesthesia and recovery was subjectively assessed by an observer blinded to the treatment. No fatalities occurred during the procedures. Intramuscular midazolam did not confer benefits in terms of improved intubating conditions, induction or recovery. The short period of time between premedication and induction potentially accounted for this lack of obvious sedative effect during the induction. Use of midazolam at higher doses was associated with a longer period of spontaneous breathing during the recovery period with the endotracheal tube in place. In general, seals in the high dose midazolam group seemed to tolerate the endotracheal tube to a greater degree. A greater level of sedation in this group during recovery may have accounted for this. Due to the inherent difficulty intubating phocids, this would be beneficial in ensuring return of spontaneous respiration prior to extubation.