Vetnuus | February 2025 9 The anatomic and physiologic modifications of cetaceans likely provided evolutionary advantages to survival in completely aquatic ecosystems (Dolar et al., 1999; Kooyman & Ponganis, 1997; Piscitelli et al., 2010, 2013). Within the suborder of toothed whales (Odontocetes), a relatively small, shallow-diving cetacean, the bottlenose dolphin (Tursiops truncatus), is the most extensively studied in its natural environment and while housed under the care of humans. Observational and capture-release research of wild dolphin populations has provided copious information on dolphin natural history, disease ecology, anddiving physiology, as well as historical and current conditions of ocean health (Schwacke et al., 2012; Wells, 2009; Yordy et al., 2010). While housed under human care, bottlenose dolphins often receive comprehensive veterinary medical services and may even contribute to clinical and translational biomedical research (Houser, Finneran, & Ridgway, 2010; Le-Bert et al., 2018; Meegan, Ardente, et al., 2021; Venn-Watson et al., 2015, 2022). General anesthesia, however, remains a challenge in dolphins due to a limited number of experienced anesthesiologists and published studies, the significant limitations of current commercially-available ventilators, and limited anesthetic drug pharmacokinetic studies, including their effects on whole body physiology (Bailey, 2021; Doescher et al., 2018; Dold & Ridgway, 2014; Dover et al., 1999; Higgins & Hendrickson, 2013; Howard et al., 2006; Jones et al., 2023; Le-Bert et al., 2024; Lee et al., 2019; Lindemann et al., 2023; McCormick & Ridgway, 2018; Medway et al., 1970; Meegan et al., 2015, 2016; Nagel et al., 1964, 1966, 1968; Ridgway, 2002; Ridgway et al., 1975, 1974; Ridgway & McCormick, 1971, 1967; Rosenberg et al., 2017; Russell et al., 2021; Schmitt et al., 2014, 2018; Sommer et al., 1968; Tamura et al., 2017). In this review, we aim to synthesize the current understanding of anesthesia physiology with knowledge of the normal cardiopulmonary physiology and subsequent perfusion adaptations of dolphins and how these adaptations may be modulated during general anesthesia of this completely aquatic marine mammal. 2. HISTORY OF DOLPHIN ANESTHESIA General anesthesia of dolphins is an infrequently practiced discipline within veterinary medicine. Little technical and practical progress was made between the first dolphin to ever be anesthetized in 1932 and the 1960s (Lilly, 1964; Nagel et al., 1964, 1966). However, during the 1960s and 1970s, Ridgway, Nagel, McCormick and colleagues made significant progress in the successful induction of, and emergence from, anesthesia in dolphins (Medway et al., 1970; Nagel et al., 1964, 1966, 1968; Ridgway et al., 1974; Ridgway & McCormick, 1971, 1967; Sommer et al., 1968). During this period of time, induction was often achieved with intravenous barbiturates (i.e., sodium thiopental, 10–25 mg/kg) and a surgical plane of anesthesia maintained with the volatile gas, halothane, or a nitrous oxide-oxygen mixture (Table 1). Mechanical ventilation was achieved through adaptation of a Bird Mark 9 large animal ventilator (Bird Respirator Company, Palm Springs, CA) with a custom-designed Leading Article >>>10 Induction agent(s) Maintenance agent(s) MAP range (mmHg) Reversal agent(s) Reference Sodium thiopental, 10–15 mg/kg, IV Halothane 115 N/A Medway et al., 1970; Ridgway & McCormick, 1971 Propofol, 3.03–4.72 mg/kg, IV N/A N/A Howard et al., 2006 N/A Sodium thiopental, 10 mg/kg, IV Halothane Halothane N/A N/A Ridgway & McCormick, 1967 Sodium thiopental, 10–15 mg/kg, IV Halothane, 1–2% N/A Ridgway et al., 1974 Pentobarbital, 10 mg/kg, IP Nitrous oxide-oxygen 122–142 N/A Sommer et al., 1968; Nagel et al., 1964; Nagel et al., 1966; Nagel et al., 1968 Midazolam, 0.02 mg/kg, IV Propofol, 1–4 mg/kg, IV cis-Atracurium, 0.1 mg/kg, IV Sevoflurane N/A 1:13 (Midazolam: Flumazenil), IV Naloxone, 0.01 mg/kg, IV Jones et al., 2023 Midazolam, 0.02 mg/kg, IV Propofol, 2–4 mg/kg, IV Sevoflurane, 1.8–2.0% 80.8+/− 2.9; 86+/−2.6 Flumazenil, 0.02–0.05 mg/ kg, IM/IV Naloxone, 0.01–0.04 mg/kg, IV (n = 7) Naltrexone, 0.05–0.20 mg/ kg, IV (n = 6) Le-Bert et al., 2024 Propofol, 1.97–5.33 mg/kg, IV Sevoflurane N/A N/A Schmitt et al., 2018
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