Abstract
The Vancouver Aquarium Marine Mammal Rescue Centre treated 148 harbor seal (Phoca vitulina) neonates and pups during the 2012 stranding season. Medical care of 16 of these seals warranted sedation to permit physical examination, removal of entanglements, minimally invasive diagnostic procedures, or pre-medication for general anesthesia to facilitate advanced imaging or surgery. A single sedation protocol was implemented for each of these procedures using a combination of injectable butorphanol (0.15 mg/kg) and midazolam (0.15 mg/kg). Seals were screened prior to administration of sedatives by general physical examination, CBC and clinical chemistry collected on admission examination and stabilized as indicated to help ensure they were good anesthetic candidates.
Harbor seals involved in the study were approximately 4–20 weeks of age, included 6 females and 10 males, and ranged in weight from 8.5–32.0 kg. Each seal was fasted a minimum of 4 hours prior to sedation. The butorphanol and midazolam combination was administered via a single intramuscular injection (IM) into the muscles overlying the pelvis, biceps femoris or semitendinosus, or intravenously (IV) into the intravertebral epidural vein. Seals were monitored by recording heart and respiratory rate every five minutes from drug administration to recovery. Sedation efficacy was characterized by length of onset, depth of sedation (ease in manipulating animal), and duration of effects.
Over a 7 month period 22 sedations were completed with 3 of the 16 animals sedated on more than one occasion. Apnea was not observed during the four procedures completed solely on injectable medication. During 14 procedures supplemental inhalation anesthesia by mask was provided; 2 of these animals then required intubation due to apnea. The remaining three seals were masked to effect to permit intubation for surgery or endoscopy. All animals intubated required assisted ventilation. Of the 22 sedations, one animal maintained on injectable sedation and two animals which also received gas anesthesia failed to recover or died overnight. One animal was euthanized due to poor prognosis. Sedated and/or anesthetized seals maintained mean (+/- SD) heart rates of 101 (+/- 22) bpm and unassisted respiratory rates of 16 (+/- 11) rpm. Maximum sedation was achieved within five minutes for IV injection and 20 minutes with IM injection. Sedation duration (drug administration to full recovery) ranged from 25–105 minutes in short procedures with minimal to no inhalation anesthesia. In 21/22 cases adequate sedation was achieved to permit gentle handling or application of mask for delivery of inhalation anesthesia.
When used in healthy harbor seals administration of injectable butorphanol and midazolam proved to be an effective protocol to obtain safe and reliable sedation for physical examination, diagnostics, or as a premedication for general anesthesia.
Acknowledgements
Thank you to the Vancouver Aquarium Marine Mammal Rescue Centre's veterinary technicians (Lindsaye Akhurst, Shanie Fradette, Kate Cooper, Sion Cahoon, Emily Johnson, Chelsea Roberts, and Michelle Collett), the Vancouver Aquarium veterinary technicians (Chelsea DeColle and Gwyneth Nordstrom) and visiting veterinary externs for their diligent assistance in anesthesia monitoring.
* Presenting author
+ Student presenter