Abstract

Although still applied infrequently, anesthesia of managed cetaceans has become an acceptable risk. Historical failures and limited experience had led to myths and misconceptions about anesthesia of cetaceans. As well, the relative difficulty with invasive support and monitoring had previously caused hesitation in performance of often medically necessary invasive procedures, only increasing the probability of negative outcomes and further perpetuating these misconceptions. A coalition-of-the-willing was built at the IAAAM conference over the recent past^1-12 and IAAAM members renewed the effort to update the anesthetic management of cetaceans to better address medically necessary procedures of cetaceans. The following is evidence of their strong efforts.

We present here a series of ten anesthesia events involving eight bottlenose dolphins (Tursiops truncatus) and one Pacific white-sided dolphin (Lagenorhynchus obliqidens). Currently, benzodiazepines alone (diazepam, midazolam), or benzodiazepines in combination with opioids (butorphanol, meperidine), are used for pre-anesthetic sedation. Intravenous access via ultrasound-guided cannulation of the lateral subcutaneous caudal vein has become routine. The injectable anesthetic agent, propofol, is used for rapid sequence induction allowing manual orotracheal intubation by rostral luxation of the elongated epiglottal and cricoarytenoid cartilages or "goosebeak." The inhalation anesthetic agents isoflurane and sevoflurane are used reliably for maintenance of anesthesia. Though statistical analysis cannot easily be applied, the median subject in this review was 26.5 years old, 177 kg, minimally received either 0.25 mg/kg diazepam PO (n = 4) or 0.08 mg/kg midazolam (n = 6) for sedation, 3.9 mg/kg propofol for induction, and an end-expired sevoflurane concentration (n = 9) of between 1.7% and 2.3% for maintenance of anesthesia for a total of 108 minutes. Conventional Controlled Mechanical Ventilation (CMV) was applied with variable success and implores review. Anesthetic monitoring and vascular access are complicated by anatomic specialization; however, direct arterial blood pressure monitoring is feasible via cannulation of the median artery of the pectoral flipper. The median blood pressure of those measured (n = 6) was low with a mean arterial blood pressure (MAP) of 44 mm Hg, but support improved values to 75 mm Hg. All improved upon entry into recovery where MAP ranged from 77 to 133 mm Hg. Upon entering recovery the median body temperature was 35.4°C, and successful extubation required 67 minutes (including those requiring re-intubation and additional time), thus necessitating continued anesthesia monitoring and support. Common concerns include endotracheal intubation and extubation, body positioning and padding, body temperature management, vascular access, blood pressure, variable response to opioids, pharmacokinetics of anesthetic agents and ventilation. New modes of ventilation, imaging techniques and advanced non-invasive monitoring methods will advance the care of these species under general anesthesia, and lessons learned with plans for improving management will be presented in brief.

AT = Atropine; B = Butorphanol; D = Diazepam; F = Flumazenil; Iso = Isoflurane; Mp = Meperidine; M = Midazolam; Nalx = Naloxone; Nalt = Naltrexone; P = Propofol; Sevo = Sevoflurane. PO = per os; IM = intramuscular; IV = intravenous. FeAgent = fraction expired inhalation anesthetic. Anesthesia duration was documented as the time from injection of IV induction agent until the vaporizer was turned off and the anesthetic circuit was flushed with oxygen to minimize inhalation anesthetic for recovery phase to begin. CMV = Conventional Mechanical Ventilation; PIP = Peak Inspiratory Pressure. LP = lateral peduncle vein (more correctly the lateral subcutaneous caudal vein or caudal superficial peduncle vein); CP = caudal peduncle vein. MAP = mean arterial blood pressure during anesthesia (note: parenthesis indicate MAP in semi-conscious and spontaneously ventilating subject in recovery phase with arterial catheter maintained until extubation). Time of detection of hypotension generally coincided with the time of placement of the arterial catheter. Reversal agent dosages were total dosages that include repeat dosing. Temp = Temperature was measured at end of anesthesia by esophageal (e) or rectal (r) temperature probe. Extub = Time to extubation was measured from the point the anesthetic circuit was initially flushed with oxygen to minimize inspired inhalation anesthetic until extubation.

Acknowledgments

The institutions driving this recent advancement in anesthetic care of cetaceans are the U.S. Navy Marine Mammal Program, National Marine Mammal Foundation, SeaWorld USA and Vancouver Aquarium. Many individuals of the marine mammal community, and other interested personage, have contributed to the development of cetacean anesthetic techniques over the years - and so many more have worked to advance the methodology by contributing to the cases discussed here. Acknowledgment and gratitude go to all, but their names are far too numerous to list here. However, there is one individual who pioneered the methods of dolphin anesthesia we use today, and has mentored, guided, or in some way promoted all of our efforts. His name is Dr. Sam H. Ridgway - anchor and concatenator of the past, present and future of cetacean anesthesia. Thank you Sam.

* Presenting author

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