Abstract
Pinniped anaesthesia is an area of ongoing interest due to the unique and complex physiology of these animals which increases the risk of complications under anaesthesia. A review of anaesthetic procedures in largha seals (Phoca largha), harbor seals (Phoca vitulina), and California sea lions (Zalophus californianus) housed at Ocean Park Hong Kong between 1997 and 2021 was performed. A total of 156 anaesthetic procedures were identified for review.
Between 1997–2005, California sea lions were immobilised prior to inhalant anaesthesia using medetomidine (0.001–0.02 mg/kg) in combination with either ketamine (1–2 mg/kg) or tiletamine and zolazepam (0.8–2 mg/kg) via intramuscular injection. Atropine (0.02 mg/kg) was incorporated into the pre-medication in 60% of the cases. The usage of this protocol was stopped after 2005 due to the high mortality rate (26.67%) under anaesthesia. Other common complications included profound bradycardia, abnormal capnography, apnoea, hyperthermia, and vomiting.
A new protocol has been adopted since 2005, for both phocids and otariids, involving pre-medication with intramuscular or intravenous butorphanol (0.15–0.3 mg/kg) combined with a benzodiazepine, commonly diazepam (0.15–0.2 mg/kg) or midazolam (0.1–0.3 mg/kg). Additional isoflurane via a face mask is required to achieve a plane of anaesthesia sufficient for intubation. During the maintenance phase, in cases where apnoea is encountered or where patient ventilation is deemed inadequate, intermittent positive ventilation is provided, usually via a mechanical ventilator. Assisted ventilation is very commonly required. Monitoring of anaesthesia relies on a combination of expired gases including capnography, electrocardiography, pulse oximetry, rectal temperature, and serial blood sampling for blood gas and pH analysis. The mortality rate with this new protocol is 3.13% for sea lions, 4.16% for largha seals, and 1.89% for harbor seals. Whilst this is still high, it is a clear improvement over the past practice due to safer drug combinations, better monitoring, and increased experience of clinicians.
*Presenting author