Immobilisation of pinniped species

Using a combination of midazolam and butorphanol is a safe and effective reversible field sedation protocol for Weddell seal (Leptonychotes weddellii) pups

BACKGROUND

Weddell seals (Leptonychotes weddellii) are a well-studied species of phocid with an apparent sensitivity to immobilising agents. Mortality as high as 31% has been reported during field immobilisation. This study investigated the use of a benzodiazepine in combination with an opioid agonist/antagonist for sedation in Weddell seal pups as part of a physiological study.

METHODS

During the 2017 and 2019 Antarctic pupping seasons, 18 Weddell seal pups were sedated by intramuscular administration of a combination of midazolam and butorphanol or intravenous midazolam alone. Individuals were sedated at 1, 3, 5 and 7 weeks of age. Naltrexone and flumazenil were used to reverse sedation. The combination was 100% effective in providing appropriate sedation for the intended procedures.

RESULTS

Analyses were performed to investigate relationships between dose administered, age, individual reactions, adverse effects and changes in dive physiology. Transient apnoea (10-60 seconds) was the most frequently observed adverse effect. No sedation-associated morbidity or mortality occurred.

LIMITATIONS

The sample size is small and there is no pharmacokinetic information for either sedative or reversal in phocid species.

CONCLUSIONS

The combination of midazolam (0.2-0.3 mg/kg) and butorphanol (0.1-0.2 mg/kg) provided safe and effective sedation, with reversible effects, in Weddell seal pups.

ANESTHESIA OF AQUARIUM-HOUSED WALRUS ( ODOBENUS ROSMARUS): A CASE SERIES

  Walruses are a challenging species to anesthetize as a result of their large mass, limited access for drug delivery, unique physiology, and small number of reports describing anesthetic procedures. Three aquarium-housed walruses ( Odobenus rosmarus) ranging in age from 3 to 11 yr old (344-1,000 kg) were anesthetized for dental or ophthalmic surgical procedures, with one animal anesthetized twice and one anesthetized three times. Preanesthetic medication was with intramuscular midazolam (0.1-0.2 mg/kg) and meperidine (2-3 mg/kg). A catheter was placed in the extradural intravertebral vein, and anesthesia was induced with propofol to effect. Orotracheal intubation was performed and anesthesia maintained with isoflurane in oxygen using a circle breathing system connected to a ventilator. Intermittent positive pressure ventilation was used in all procedures. For the ophthalmic surgery, the neuromuscular blocking agent, cisatracurium, was given intravenously to provide a central eye and optimal surgical conditions. The neuromuscular block was antagonized with edrophonium. Total anesthesia times ranged from 1.5 to 6 hr. Midazolam and meperidine were antagonized with flumazenil and naltrexone, respectively, in five of six cases. Nonsteroidal anti-inflammatory agents were provided for analgesia. Recoveries were calm and uneventful. The described anesthetic protocols and case management were successful under the conditions encountered.

A review of methods used to capture and restrain introduced wild deer in Australia

Six non-native deer species have established wild populations in Australia, and most are expanding in distribution and abundance. There is therefore increasing focus on the need to understand and manage these species. Capturing and immobilising wild deer is essential for many research and management applications, but the best methods for doing this have not been identified for the Australian situation. To address this knowledge gap, we systematically reviewed methods used to physically capture and chemically immobilise the six wild deer species in Australia. A variety of physical and chemical restraint methods have been used to capture wild deer in Australia, but these have seldom been reported in peer-reviewed publications. Physical capture methods have employed a variety of trapping and netting configurations. Some chemical immobilisation approaches have used oral baiting, but most have relied on darting of free-ranging animals or hand-injection of physically restrained deer. There is uncertainty about the efficacy and animal welfare impacts of the techniques currently used to capture wild deer in Australia. Improved reporting of capture outcomes would facilitate the identification of ‘best practice’ techniques for capturing wild deer in Australian environments.

Investigation into the characteristics, triggers and mechanism of apnoea and bradycardia in the anaesthetized platypus (Ornithorhynchus anatinus)

Health and conservation research on platypuses (Ornithorhynchus anatinus) may require anaesthesia to reduce stress and the risk of injury to both the animal and the researcher, as well as to facilitate examination and sample collection. Platypus anaesthesia can be difficult to manage, with reports of periods of apnoea and bradycardia described. This study investigated the conditions around sudden-onset apnoea and bradycardia in 163 field-anaesthetized platypuses as part of a health study. Anaesthesia was induced and maintained using isoflurane delivered in oxygen by face mask. Sudden-onset apnoea and bradycardia was observed in 19% of platypuses, occurring either at induction of anaesthesia, during recovery, or both. At induction, occurrence was more often recorded for adults (P = 0.19) and was correlated with low body temperature (P < 0.001), season (P = 0.06; greater incidence in summer) and longer pre-anaesthetic holding time (P = 0.16). At recovery, sudden-onset apnoea and bradycardia occurred only in platypuses that had been placed in dorsal recumbency as part of their examination, and correlated with poor body condition (P = 0.002), time in dorsal recumbency (P = 0.005), adults (P = 0.06), number of fieldworkers (P = 0.06) and females (P = 0.11). The sudden-onset apnoea and bradycardia we observed is likely to result from the irritant nature of isoflurane (stimulating the trigeminal nerve via nasal chemoreceptors). We propose that this mechanism is analogous to that of submersion of the face/nasal cavity in cold water during a natural dive response, but that the term 'nasopharyngeal response' would more appropriately describe the changes observed under isoflurane anaesthesia. Although we did not record any long-term adverse effects on platypuses that had undergone this response, the nasopharyngeal response could complicate the diagnosis of anaesthetic dose-dependent apnoea and bradycardia. Therefore, we suggest that these responses during anaesthesia of platypuses might be avoided by minimizing the stress around capture and handling, as well as reducing the time in dorsal recumbency.

[Focal meningitis in a California sea lion (Zalophus californianus)--diagnostic procedure and pathology]

A 15-year-old female California sea lion (Zalophus californianus) with progressive lameness of the hindlimbs and a chronic skin lesion was presented for clinical examination. The clinical neurological examination, showing a paraparesis, was completed by magnetic resonance imaging. MR images of the cervical and thoracic spine showed a well-defined muscle infiltrating lesion between the seventh cervical vertebra (C7) and the second thoracic vertebra (T2), which extended through the intervertebral foramina between C7 and T1 into the vertebral canal, causing spinal cord compression and displacement. Pathological examination revealed focal purulent meningitis resulting from widespread fistulas of the chronic skin leasion, which was infected with Escherichia coli var. haemolytica and Clostridium perfringens.

Risk factors associated with perianesthetic mortality of stranded free-ranging California sea lions (Zalophus californianus) undergoing rehabilitation

The objective of this study was to identify risk factors associated with perianesthetic mortality of stranded free-ranging California sea lions (Zalophus californianus) undergoing rehabilitation. Hospital records of California sea lions that underwent heavy sedation or general anesthesia from 2004 through 2008 were reviewed, including records from 419 anesthetic events. Procedures that resulted in death during or in the subsequent 72 hr of anesthesia were classified as cases (n = 15). Procedures in which the animal survived were classified as controls (n = 334). Procedures that resulted in euthanasia (n = 70) were removed from subsequent analysis. The following risk factors were reviewed: gender, age class, health status, duration of anesthetic period, atropine premedication, induction protocols, maintenance protocols, and history of prior anesthesia. The prevalence of fatalities during anesthesia was 3.4% (n = 12) over the 5-yr period. With the inclusion of animals that died within 72 hr after anesthesia, the total mortality prevalence rose to 4.3% (n = 15). The most common time of death was during anesthetic maintenance. Health status was the single best predictor of anesthetic outcome, and sea lions premedicated with atropine had increased odds of anesthetic-related death.

Effect of induction dose, lactation stage and body condition on tiletamine-zolazepam anaesthesia in adult female grey seals (Halichoerus grypus) under field conditions

Tiletamine-zolazepam (TZ) was used at a mean (sd) dose of 1.18 (0.15) mg/kg administered intramuscularly to anaesthetise adult female grey seals (Halichoerus grypus) under field conditions at three different stages during their lactation period. A significant correlation was observed between the induction dose and time to induction (r=-0.582, P=0.011). Stage of lactation had a significant effect on condition index (CI), calculated as axial girth divided by length (P<0.001), and time to induction (P=0.009). No effect of CI on induction or recovery time was demonstrated. Respiratory rate decreased during induction and increased significantly (P<0.001) during surgical biopsy of blubber. Recovery occurred after 32.5 (11.9) minutes. Minor complications (tremor, vocalisation and mild dyspnoea) were observed in a small number of cases, none of which required treatment.

Anaesthesia of three young grey seals (Halichoerus grypus) for fracture repair

Three young grey seals (Halichoerus grypus) were presented separately for fracture repair to the veterinary teaching hospital of University College Dublin. The seals were premedicated with a combination of pethidine, midazolam and atropine; anaesthesia was induced with propofol via the front flipper vein and maintained with sevoflurane or isoflurane in oxygen. One of the seals did not breathe spontaneously after anaesthesia; a cardiac arrest, resulting in death, occurred after several hours of mechanical ventilation. Post-mortem examination revealed a severe lungworm infestation and parasitic pneumonia in this animal. The two other seals recovered uneventfully from anaesthesia.

The effects of two dosages of midazolam on short-duration anesthesia in the harp seal (Phoca groenlandica)

The purpose of this study was to provide safe anesthesia for bronchoalveolar lavage and assess the utility of premedication with i.m. midazolam for short-duration anesthesia with isoflurane in harp seals (Phoca groenlandica). Fourteen yearling harp seal pups were anesthetized three times each as part of a prospective, cross-over, blinded study. Each animal received i.m. premedication with saline, low-dose, or high-dose midazolam (respectively 0.1 and 0.2 mg/ kg). Following premedication, anesthesia was induced with 4% isoflurane in oxygen delivered through a mask and connected to a Bain non-rebreathing system. A significantly longer time was taken from the end of general anesthesia to head movement in the high-dose group compared with the saline group (P = 0.002). A significantly longer time was taken from the end of general anesthesia to ambulation in the high-dose group compared with the saline group (P = 0.006). There were no significant differences between groups in the subjective assessment of anesthetic quality or ease of intubation. Premedication with i.m. midazolam at the dosages used did prolong recovery from anesthesia, although to a degree unlikely to be significant clinically.

Use of end-tidal partial pressure of carbon dioxide to predict arterial partial pressure of carbon dioxide in harp seals during isoflurane-induced anesthesia

OBJECTIVE

To evaluate the relationship between end-tidal partial pressure of CO(2) (ETCO(2)) and PaCO(2) in isoflurane-anesthetized harp seals.

ANIMALS

Three 5-month-old 25- to 47-kg harp seals (Phoca groenlandica).

PROCEDURES

PaCO(2) was determined in serial arterial samples from isoflurane-anesthetized seals and compared with concomitant ETCO(2) measured with a side-stream microstream capnograph. Twenty-four paired samples were subjected to linear regression analysis and the Bland-Altman method for assessment of clinical suitability of the 2 methods (ie, PaCO(2) and ETCO(2) determinations). The influence of ventilation rate per minute (VR) on the ETCO(2) to PaCO(2) difference (P[ET-a] CO(2)) was examined graphically.

RESULTS

The correlation coefficient between the 2 measurements was 0.94. The level of agreement between ETCO(2) and PaCO(2) varied considerably. Values of ETCO(2) obtained with a VR of < 5 underestimated PaCO(2) to a greater degree (mean bias, -4.01 mm Hg) and had wider limits of agreement of -13.10 to 5.07 mm Hg (-4.01 mm Hg +/- 1.96 SD), compared with a VR of > or = 5 (mean bias, -2.24 mm Hg; limits of agreement, -7.79 to 3.30 mm Hg).

CONCLUSIONS AND CLINICAL RELEVANCE

These results indicate that a microstream sidestream capnograph provides a noninvasive, sufficiently accurate estimation of PaCO(2) with intermittent positive ventilation at a VR > or = 5 in anesthetized harp seals.

Chemical immobilization of adult female Weddell seals with tiletamine and zolazepam: effects of age, condition and stage of lactation

BACKGROUND

Chemical immobilization of Weddell seals (Leptonychotes weddellii) has previously been, for the most part, problematic and this has been mainly attributed to the type of immobilizing agent used. In addition to individual sensitivity, physiological status may play an important role. We investigated the use of the intravenous administration of a 1:1 mixture of tiletamine and zolazepam (Telazol) to immobilize adult females at different points during a physiologically demanding 5-6 week lactation period. We also compared performance between IV and IM injection of the same mixture.

RESULTS

The tiletamine:zolazepam mixture administered intravenously was an effective method for immobilization with no fatalities or pronounced apnoeas in 106 procedures; however, there was a 25 % (one animal in four) mortality rate with intramuscular administration. Induction time was slightly longer for females at the end of lactation (54.9 +/- 2.3 seconds) than at post-parturition (48.2 +/- 2.9 seconds). In addition, the number of previous captures had a positive effect on induction time. There was no evidence for effects due to age, condition (total body lipid), stage of lactation or number of captures on recovery time.

CONCLUSION

We suggest that intravenous administration of tiletamine and zolazepam is an effective and safe immobilizing agent for female Weddell seals. Although individual traits could not explain variation in recovery time, we suggest careful monitoring of recovery times during longitudinal studies (> 2 captures). We show that physiological pressures do not substantially affect response to chemical immobilization with this mixture; however, consideration must be taken for differences that may exist for immobilization of adult males and juveniles. Nevertheless, we recommend a mass-specific dose of 0.50-0.65 mg/kg for future procedures with adult female Weddell seals and a starting dose of 0.50 mg/kg for other age classes and other phocid seals.

Reversible anesthesia of captive California sea lions (Zalophus californianus) with medetomidine, midazolam, butorphanol, and isoflurane

Two adult California sea lions (Zalophus californianus) were effectively anesthetized 13 times with medetomidine (0.010-0.013 mg/kg), midazolam (0.2-0.26 mg/kg), and butorphanol (0.2-0.4 mg/kg) by i.m. hand or pole syringe injection. For each anesthetic event, atropine (0.02 mg/kg, i.m.) was administered 6-20 min after initial injections, and oxygen administration via face mask or nasal insufflation began at the same time. Light anesthesia was induced in 8-22 min and lasted 13-78 min. During eight of the procedures, isoflurane (0.5-2.0%) was administered via face mask or endotracheal tube for an additional 30-120 min to facilitate longer procedures or surgery. Anesthesia was antagonized with atipamezole (0.05-0.06 mg/kg) and naltrexone (0.1 mg/kg) in seven events, with the addition of flumazenil (0.0002-0.002 mg/kg) in six events. The antagonists were administered by i.m. injection 42-149 min after administration of the induction agents. All sea lions recovered to mild sedation within 4-17 min after administration of the antagonists.

Blood chemistry in southern elephant seal mothers and pups during lactation reveals no effect of handling

Serum clinical chemistry parameters were examined in lactating southern elephant seal Mirounga leonina mothers and their pups from the declining Macquarie Island population. There were significant changes in serum values from 2 to 21 days postpartum in both nursing mothers (increase: inorganic phosphate; decrease: creatinine, potassium, chloride, cholesterol, total protein, albumin, globulin, aspartate aminotransferase, creatine kinase) and suckling pups (increase: inorganic phosphate, globulin, cholesterol; decrease: albumin, alkaline phosphatase, gammaglutamyl transferase; increase followed by decrease: triglycerides, iron). We found no evidence that changes were due to chronic stress effects caused by repeated chemical immobilisations (mothers) or physical restraint (pups): at late lactation, clinical chemistry values were similar for mother-pup pairs of a control group (not handled previously), moderate treatment group (previously handled twice) and high treatment group (previously handled three to four times). We were not able to detect differences in clinical chemistry values between mother-pup pairs distributed over two areas differing in the frequency of human visits. The clinical chemistry values presented here can serve as reference ranges to allow future comparison with other southern elephant seal populations to investigate factors, e.g. food limitation, suspected to be involved in population declines.