Use of midazolam and butorphanol to sedate harbor seal pups (Phoca vitulina) undergoing rehabilitation

Abstract

Between 2012 and 2022, the Vancouver Aquarium Marine Mammal Rescue Centre sedated 110 harbor seal pups for physical examinations, diagnostic procedures, or treatment. A sedation protocol of butorphanol and midazolam (0.1–0.2 mg/kg each) was administered via a single i.v. injection in 171 procedures. Of these, 21 pups were anesthetized only with the injectables, while supplemental isoflurane inhalation anesthesia by mask was provided during 58 procedures; 92 other animals required intubation for respiratory support due to apnea or to achieve a deeper plane of anesthesia to facilitate more invasive procedures. Of the 171 sedations, five were euthanized due to poor prognosis and six failed to recover. Maximum sedation, sufficient for intended procedure or anesthesia induction, was achieved within a mean of 8.5 ± 5.8 min for i.v. injection (n = 133). Sedation duration (drug administration to full recovery) without supplemental inhalation anesthesia had a mean of 30.2 min and ranged from 14 to 52 min (n = 13). When used in stabilized young harbor seals, administration of injectable butorphanol and midazolam proved to be an effective protocol to obtain safe and reliable sedation for physical examination, minimally invasive diagnostic procedures, or as a premedication for general anesthesia.