Abstract

Walruses (Odobenus rosmarus) have one tusk, a modified canine, in each maxilla, which are hypsodont and aradicular. The dental formula of the adult walrus is: I(1/0), C(1/1), P(3/3)=18. The tusks are used to haul the animal out of the water through the ice holes, but in managed care they often rub on the floor or walls of enclosures. The dentine can become exposed which commonly leads to pulpitis and pulp necrosis with a swelling laterally on the nasal bridge just rostral to the eye. The swelling result in an exudative sinus tract, which often resolves with antibiotics. However, once the antibiotics are withdrawn, the swelling usually returns along with the draining sinus tract. Extraction of the tusks can be curative but, sometimes unexpected complications arise.

The treatment of two walruses will be described. Case one was a juvenile female Pacific walrus weighing 243 kg given midazolam (0.18 mg/kg) and butorphanol (0.22 mg/kg) mixed in the same syringe and administered by intravenous bolus via the pedal interdigital vein under voluntary behavior. Case two was a juvenile female Pacific walrus weighing 279 kg given midazolam (0.23 mg/kg) and butorphanol (0.25 mg/kg) administered intramuscularly in the dorsal rump using a 7.5 cm 18G needle. Ventilation rate and ventilation pressure were managed to keep ETCO2 between 35 and 45 mm Hg. Blood pH and K⁺ were also measured at 30-minute intervals and did not change significantly throughout the procedures. Ventilation pressure was also adjusted to achieve desired chest excursion, assessed simply by direct visualisation. The positive inspiratory pressure used was 30 and 38 mm Hg respectively. Fresh gas delivery was adjusted to reach expired isoflurane values between 0.9 and 1.2%, sufficient to eliminate any response to painful stimuli. Other monitoring included ECG and SPO2. Flumazenil (0.01 and 0.005 mg/kg) and naloxone (0.02 mg/kg) were given IM once the remaining surgical time was estimated to be under 15 minutes. Suction was used to clear the oral cavity of secretions. Spontaneous breathing resumed once expired isoflurane values decreased to under 0.6%. Extubation did not present any peculiarity.

Local anaesthesia was induced by deep peri-jugal infusion of lidocaine 2% using a 100 mm 21G spinal needle. The soft tissue (gingiva) surrounding each tusk was severed using a dental luxator which was subsequently circumferentially driven between the alveolar bone and the tusk to the full length of the instrument. Once the tusk had become slightly mobile, indicating that the periodontal ligaments had been severed, a 5 mm hole was drilled into each tusk—usually beginning at the fracture surface. A novel tusk extraction technique will be described. Once the tusks were avulsed, the apical extent of the alveoli were curettage to remove all pulp (necrotic, inflamed and vital) and remaining germinal tissue. An endoscope was used to visually examine the apical extent of the alveolus and additional curettage was performed where necessary. Complications which developed during the post-operative period in one walrus will be described.

*Presenting author