Successful Immobilization of Captive and Free-Ranging Pinnipeds: Practical Tips to Improve Success
Immobilization of captive and free-ranging pinnipeds continues to be viewed as a “higher-risk” anesthesia by many zoo and wildlife veterinarians. Common concerns have included unpredictable quality and duration of anesthesia, apnea, bradycardia, prolonged recovery times, and death. However, numerous published and unpublished data sets illustrate that pinnipeds can be very safely anesthetized using newer anesthesia protocols and procedures. In a zoo setting, the degree of pre-anesthetic assessment that is possible varies greatly, but should not be overlooked. Such a luxury does not exist with wild specimens, but the success of various recent field anesthesia projects illustrates that lack of pre-anesthetic information should not be viewed as a valid reason to avoid an immobilization. Various combinations of medetomidine, butorphanol, and midazolam provide a safe, reliable protocol that can be used as a pre-anesthetic or complete induction agent based upon dosages. Other newer anesthetic drugs (e.g., alfaxalone) also show great promise. Gas anesthesia (isoflurane, sevoflurane) provides not only a reliable maintenance anesthetic, but can also be used as an induction agent with proper equipment (special nets, restraint devices, masks) and training. Efficient intubation and maintenance of proper ventilatory support are a necessity, often requiring modification of equipment for use in the field. Anesthetic monitoring is greatly enhanced through the use of Doppler monitors, capnography, arterial blood gas analysis, and reflectance pulse oximetry, all of which can require specialized knowledge or equipment to ensure success. Vascular access can be challenging, but with proper training, reliable arterial blood samples for gas analysis are obtainable, as well as efficient placement of central line catheters for intravenous access. With secure vascular access, continuous rate infusion of anesthetics and supportive drugs is possible in a zoo setting, which can further enhance patient safety. Overall, with proper planning and precautions, pinnipeds can be safely anesthetized for sustained periods of time. An increased comfort with such procedures will also help to further shift zoo philosophy away from the “anesthesia as a last resort” paradigm, leading to improved clinical care and healthier anesthetic candidates.
The author thanks Dr. Gwen Jankowski, Dr. Jennifer Langan, Dr. Jenny Meegan, and Susana Cardenas for their continued assistance and support of numerous pinniped projects and procedures in the zoo and in the field.