Abstract

Anaesthesia of pinnipeds has presented many problems over the years. With increasing knowledge of their unique physiology and improved monitoring equipment, the success of pinniped anaesthesia has increased markedly. Many different agents have been used to induce anaesthesia in seals and maintain them for various procedures.

Tiletamine and zolazepam, a 1:1 mixture (Zoletil®), has been used to successfully and safely sedate many species of animals. It is known to increase the heart rate and strength of the heart contractions. Under Zoletil sedation, swallowing reflexes are maintained. There is very little muscle relaxation with this drug, and there is also little to no pain relief. There is no specific reversal agent for Zoletil, and recovery can be prolonged and violent.

Pinnipeds need to be sedated or anaesthetized for many reasons, including capture, diagnostic imaging, collection of clinical material, and surgery. Many pinnipeds in captivity develop cataracts that affect their vision and ultimately their quality of life. These cataracts often necessitate lensectomies to restore the sight of these animals and ultimately their quality of life.

In August and September 2011, fourteen seals were anaesthetized for ocular procedures or for examination for disease investigation. The fourteen individual seals included two California Sea Lions, seven Australian Sea Lions, four New Zealand Fur Seals, and one Subantarctic Fur Seal. One seal was anaesthetized twice due to surgical complications. Eight animals had bilateral lensectomies performed. Three animals had unilateral lensectomies performed. One animal had one eye enucleated. One animal had cyclosporine implants placed subconjunctivally in both eyes. The other animal was anaesthetized to examine a unilateral nasal discharge. One animal that had a bilateral lensectomy performed was anaesthetized three weeks later because of unabated bleeding into the anterior chamber, which needed to be resolved. In all fifteen anaesthesias were performed.

Most animals were weighed prior to anaesthesia to determine body weight. One animal was unable to be weighed, and its weight was estimated on previous body weights recorded for this animal. Individuals were given Zoletil by hand injection (n = 2), pole syringe (n = 3) or by projectile syringe (n = 10). The doses of Zoletil given to these animals ranged from 1.7 mg/kg to 3.2 mg/kg. All animals given this dose were sedated enough to allow a mask to be placed over their muzzle. Animals were then masked down with isoflurane and oxygen until they were in a deep enough plane of anaesthesia to intubate. All animals were intubated with the appropriately sized endotracheal tube. In most instances (n = 13), an intravenous catheter was inserted into the jugular vein. This was either accomplished by palpation or by ultrasound-guided positioning. Intravenous fluids and drugs were administered through these jugular catheters. All seals were given intermittent positive pressure ventilation during the anaesthetic.

The length of anaesthesia from the time of Zoletil administration until the time of extubation varied from 1 hour and 8 minutes to 4 hours and 33 minutes. The length of anaesthesia from the time of Zoletil administration until the time the isoflurane was discontinued varied from 47 minutes to 3 hours and 35 minutes. Heart rate, body temperature, oxygen saturation, and end-tidal CO₂ levels were monitored throughout the procedures. The minimum alveolar concentration of isoflurane was also monitored throughout the procedures. All animals recovered uneventfully from the anaesthesia and surgery. Recovery lengths, being the time the isoflurane was discontinued until the time of extubation, varied from 10 minutes to 2 hours and 20 minutes.

Successful anaesthesia in seals provides significant challenges to veterinarians compared to terrestrial animals. We suggest that intramuscular administration of Zoletil is an effective and safe immobilizing agent for otarid sp. at 1.5–3.5 mg/kg intramuscularly. Australian Sea Lions (Neophoca cinerea) should be immobilized with the lower dose of Zoletil, i.e., 1.5–2.0 mg/kg intramuscularly.

Acknowledgements

The authors would like to thank all the staff at Sea World, Underwater World, and the Pet Porpoise Pool who were involved in the anaesthesia and the pre- and postoperative care of the animals in these procedures.