Retrospective Analysis of Perianesthetic Mortality Risk Factors in California Sea Lions (Zalophus californianus) Undergoing Rehabilitation
American Association of Zoo Veterinarians Conference 2017
Justin F. Rosenberg1, DVM; Shawn P. Johnson2, DVM, MPVM; F. Fabian Okonski3,4, MD; Sophie Whoriskey2, DVM; Claire A. Simeone2, DVM; Cara L. Field2, DVM, PhD
1Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; 2The Marine Mammal Center, Marin Headlands, Sausalito, CA, USA; 3Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Stanford, CA, USA; 4CEP Anesthesia, Good Samaritan Hospital, San Jose, CA, USA


Anesthetic techniques in marine mammals have been refined in recent years, but still carry a greater risk of associated mortality in comparison to other species.3,4 Known complications in otariids include prolonged recoveries, thermoregulatory compromise, and death.1,2 In an effort to evaluate and understand the risk factors in California sea lions (CSL) (Zalophus californianus) undergoing treatment at The Marine Mammal Center, and to reduce mortality during anesthetic procedures, a retrospective case-control study was undertaken. Medical and anesthetic records for all CSL admitted between 2013 and 2016 were evaluated. A total of 809 anesthetic procedures were performed during the study period. Perianesthetic deaths were defined as having occurred during the induction, maintenance, or recovery periods, or within 48 h of the anesthetic procedure (n=58). Animals that recovered and were alive 48 h post-procedure were classified as controls (n=647). Risk factors including sex, age class, body weight, health status, days since admission, duration of anesthesia, premedication/induction agent(s), maintenance agent, endotracheal intubation, antagonist administration, and prior anesthesia were evaluated. Overall, there was a 2.8% (n=20) mortality rate during anesthetic induction and maintenance; this increased to 6.5% and 8.2% at 24 and 48 h following recovery, respectively. Odds ratio calculations revealed that significant risk factors included age, health status, days since admission, and duration of anesthesia. Evaluating the data garnered from ongoing anesthetic efforts in stranded CSL will continue to expand the knowledge regarding anesthetic risks and inform options for decreasing perianesthetic mortality.


The authors would like to thank all of the staff and hundreds of volunteers at The Marine Mammal Center for their dedication and hard work during the busy rescue and rehabilitation seasons. All procedures were performed under authority of the Stranding Agreement between TMMC and NMFS.

Literature Cited

1.  Haulena M. Otariid seals. In: West G, Heard D, Caulkett N, eds. Zoo Animal and Wildlife Immobilizations and Anesthesia. Chapter 47. 2nd ed. Ames, IA: Wiley-Blackwell; 2014:661–672.

2.  Melin SR, Haulena M, Van Bonn W, Tennis MJ, Brown RF, Harris JD. Reversible immobilization of free-ranging adult male California sea lions (Zalophus californianus). Mar Mammal Sci. 2013;29:E529–E536.

3.  Stringer EM, Van Bonn W, Chinnadurai SK, Gulland FMD. Risk factors associated with perianesthetic mortality of stranded free-ranging California seal lions (Zalophus californianus) undergoing rehabilitation. J Zoo Wildl Med. 2012;43:233–239.

4.  Van Bonn, WG. Pinnipedia. In: Miller RE, Fowler ME, eds. Fowler’s Zoo and Wild Animal Medicine, Volume 8. St. Louis, MO: Elsevier Saunders; 2014:436–449.


Speaker Information
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Justin F. Rosenberg, DVM
Department of Small Animal Clinical Sciences
College of Veterinary Medicine
University of Florida
Gainesville, FL, USA

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