Total intravenous anaesthesia with alfaxalone in two grey seals (Halichoerus grypus) undergoing enucleation

Abstract

Two young grey seals, from a seal rescue organisation, were presented to the University College Dublin Veterinary Hospital for unilateral eye enucleation. After premedication (pethidine-midazolam-atropine combination given intramuscularly), induction was performed with alfaxalone, and anaesthesia was maintained with alfaxalone total intravenous anaesthesia. During recovery, one of the seals developed severe bradycardia, apnoea and cardiac arrest resulting in death. The other recovered uneventfully after a short period of respiratory distress. Both seals had a suspected infectious pneumonia based on preoperative thoracic radiographs. This case report details the anaesthetic protocols used, the challenges presented to the anaesthetist by this species, and suggests that some complications could be potentially mitigated by more judicious use of anticholinergic agents. BACKGROUNDAnaesthesia in pinnipeds is challenging due to significant anatomical, physiological and behavioural variations compared with other species due to their adaptation to the aquatic life. [1][2][3][4][5][6][7][8] Mortality rates from 10% to 38% have been associated with profound sedation or general anaesthesia in these animals, 5,9-12 which far exceed the mortality rates reported in other veterinary species such as dogs (0.17%) or cats (0.24%). 13 Activation of the dive reflex (apnoea, bradycardia and vasoconstriction) has been identified as one of the main causes of anaesthetic-related death in seals. 2,8,12,[14][15][16] Anaesthesia in seals can present other specific difficulties. Seals have a thick blubber lining that can be up to 10 cm deep leading to potentially unreliable intramuscular (IM) injection. 17 The blubber layer is around 3.5 cm thick around the paralumbar musculature and it is the recommended site of injection using a 5-10 cm long spinal needle, depending on the size of the seal. 7,18 Intravenous (IV) cannulation can be challenging. 7,19 The superficial palmar, jugular, precaval, dorsal digital and saphenous veins can be catheterised by direct visualisation/palpation or with ultrasound guidance 18,19 , and the use of an epidural catheter to access the extradural venous sinus has also been reported in one seal. 20 Endotracheal intubation may also be difficult due to the large amount of peri-pharyngeal tissues and the long, flaccid soft palate. [4][5][6][7]16,21,22 Laryngospasm 14 and the incomplete tracheal rings, which allow the trachea to collapse during diving, can add to the challenge of intubation. [4][5][6][7]16,21,22 Due This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.