VET Februarie / February 2025 The Monthly Magazine of the SOUTH AFRICAN VETERINARY ASSOCIATION Die Maandblad van die SUID-AFRIKAANSE VETERINÊRE VERENIGING Disorders of the integumentary system of backyard poultry – Part 2 of 2 CPD THEME Aquatic Animals nuus•news Access to CPD Articles: https://www.sava.co.za/vetnews-2025/
Dagboek • Diary Ongoing / Online 2025 February 2025 March 2025 April 2025 May 2025 SAVETCON: Webinars Info: Corné Engelbrecht, SAVETCON, 071 587 2950, corne@savetcon.co.za / https://app.livestorm.co/svtsos Acupuncture – Certified Mixed Species Course Info: Chi University: https://chiu.edu/courses/cva#aboutsouthafrica@tcvm.com SAVA Johannesburg Branch CPD Events Monthly - please visit the website for more info. Venue: Johannesburg Country Club Info: Vetlink - https://savaevents.co.za/ South African Equine Veterinary Association (SAEVA) Congress 20-23 February Venue: Skukuza, Kruger National Park, Mpumalanga Info: support@vetlink.co.za or visit www.saeva.co.za Wildlife Group of the SAVA Congress 27 February – 01 March Venue: Future Africa, University of Pretoria Info: https://vetlink.co.za/wildlife-congress-2025/ or conferences@vetlink.co.za NVCG Ophthalmology Road Show 27 March Venue: To be confirmed (Durban) Info: https://vetlink.co.za/nvcg-ophthalmology-roadshow-2025/ or www.vetlink.co.za Oranje Vaal Branch Congress 11 – 12 April Venue: Khaya Ibhubesi Conference Centre, Parys Info: conference@savetcon.co.za NVCG Ophthalmology Road Show 08 May Venue: To be confirmed (Cape Town) Info: https://vetlink.co.za/nvcg-ophthalmology-roadshow-2025/ or www.vetlink.co.za June 2025 July 2025 August 2025 September 2025 NVCG Ophthalmology Road Show 15 May Venue: To be confirmed (Johannesburg) Info: https://vetlink.co.za/nvcg-ophthalmology-roadshow-2025/ or www.vetlink.co.za RuVASA Annual Conference 18 – 21 May Venue: Radisson Hotel & Convention Centre, Johannesburg, O.R. Tambo Airport (Gauteng) Info: www.vetlink.co.za Eastern Free State Branch Congress 06-07 June Venue: To be confirmed (Clarens) Info: conference@savetcon.co.za 55th Annual SASAS Congress 08 -10 July Venue: Protea Hotel, The Ranch Resort, Polokwane Info: https://www.sasascongress.co.za/ Hill’s & MSD Nurses Weekend 26-27 July Venue: To be confirmed (Cape Town) Info: corne@savetcon.co.za or visit www.savetcon.co.za NVCG Ophthalmology Road Show 26-27 July Venue: Skukuza, Kruger National Park, Mpumalanga Info: www.vetlink.co.za 14th International Veterinary Immunology Symposium 11-14 August Venue: Hilton Vienna Park, Austria Info: corne@savetcon.co.za or visit www.ivis2025.org 22nd Annual SASVEPM Congress 20 -22 August Venue: To be confirmed (Mpumalanga) Info: https://sasvepm.org/ 5th International Congress on Parasites of Wildlife and 53rd Annual PARSA Conference 14-18 September Venue: Skukuza, Kruger National Park, Mpumalanga Info: corne@savetcon.co.za or visit www.savetcon.co.za
Vetnuus | February 2025 1 Contents I Inhoud President: Dr Ziyanda Qwalela president@sava.co.za Managing Director: Mr Gert Steyn md@sava.co.za/ +27 (0)12 346 1150 Editor VetNews: Ms Andriette van der Merwe vetnews@sava.co.za Accounts / Bookkeeping: Ms Sonja Ludik bookkeeper@sava.co.za/+27 (0)12 346 1150 Secretary: Ms Sonja Ludik sonja@sava.co.za/ +27 (0)12 346 1150 Reception: Ms Hanlie Swart reception@sava.co.za/ +27 (0)12 346 1150 Marketing & Communications: Ms Sonja van Rooyen marketing@sava.co.za/ +27 (0)12 346 1150 Membership Enquiries: Ms Debbie Breeze debbie@sava.co.za/ +27 (0)12 346 1150 Vaccination Booklets: Ms Debbie Breeze debbie@sava.co.za/ +27 (0)12 346 1150 South African Veterinary Foundation: Ms Debbie Breeze savf@sava.co.za/ +27 (0)12 346 1150 Community Veterinary Clinics: Ms Claudia Cloete manager@savacvc.co.za/ +27 (0)63 110 7559 SAVETCON: Ms Corné Engelbrecht corne@savetcon.co.za/ +27 (0)71 587 2950 VetNuus is ‘n vertroulike publikasie van die SAVV en mag nie sonder spesifieke geskrewe toestemming vooraf in die openbaar aangehaal word nie. Die tydskrif word aan lede verskaf met die verstandhouding dat nóg die redaksie, nóg die SAVV of sy ampsdraers enige regsaanspreeklikheid aanvaar ten opsigte van enige stelling, feit, advertensie of aanbeveling in hierdie tydskrif vervat. VetNews is a confidential publication for the members of the SAVA and may not be quoted in public or otherwise without prior specific written permission to do so. This magazine is sent to members with the understanding that neither the editorial board nor the SAVA or its office bearers accept any liability whatsoever with regard to any statement, fact, advertisement or recommendation made in this magazine. VetNews is published by the South African Veterinary Association STREET ADDRESS 47 Gemsbok Avenue, Monument Park, Pretoria, 0181, South Africa POSTAL ADDRESS P O Box 25033, Monument Park Pretoria, 0105, South Africa TELEPHONE +27 (0)12 346-1150 FAX General: +27 (0) 86 683 1839 Accounts: +27 (0) 86 509 2015 WEB www.sava.co.za CHANGE OF ADDRESS Please notify the SAVA by email: debbie@sava.co.za or letter: SAVA, P O Box 25033, Monument Park, Pretoria, 0105, South Africa CLASSIFIED ADVERTISEMENTS (Text to a maximum of 80 words) Sonja van Rooyen assistant@sava.co.za +27 (0)12 346 1150 DISPLAY ADVERTISEMENTS Sonja van Rooyen assistant@sava.co.za +27 (0)12 346 1150 DESIGN AND LAYOUT Sonja van Rooyen PRINTED BY Business Print: +27 (0)12 843 7638 VET nuus•news Diary / Dagboek II Dagboek • Diary Regulars / Gereeld 2 From the President 4 Editor’s notes / Redakteurs notas Articles / Artikels 8 Cardiopulmonary adaptations of a diving marine mammal, the bottlenose dolphin: Physiology during anesthesia 22 Basic aquarium setup and common pitfalls Association / Vereniging 24 CVC News 26 SAVA News 36 Legal Mews Vet's Health / Gesondheid 40 Life Coaching Technical / Tegnies 38 Ophthalmology Column 42 Royal Canin Column Relax / Ontspan 48 Life Plus 26 Marketplace / Markplein 44 Marketplace Jobs / Poste 45 Jobs / Poste 47 Classifieds / Snuffeladvertensies 8 48 42 Click on the image to access Vetnews CPD articles «
Vetnews | Februarie 2025 2 « BACK TO CONTENTS In January leading into February we have been blessed to witness a planetary alignment commonly known as a “planetary parade”, visible in our night skies. If you’ve missed it, there is still time in February to view these planets in very close proximity to each other. Such events remind me that despite various disruptions things tend to eventually align for better value creation. The last few months presented many challenges for SAVA; however, these are slowly resolving and SAVA will undoubtedly emerge more resilient. We have received a large portion of the HWSETA allocation for the 2024/25 financial year and actively engaging with SASVEPM, BVF and other stakeholders to ensure that we implement the programme as per our commitment to the HWSETA. We are excited about the strengthening of the programme in this way as it will create many opportunities for collaboration while increasing the skill levels in both clinical and non-clinical aspects of veterinary science. I acknowledge and welcome to the profession and mentorship programme, all the new graduates that are just starting with their Compulsory Community Service (CCS) year. As they enter their 2nd month of employment I trust that they have found their feet and identified learning opportunities. May this year be your most transformative year thus far. I trust that the mentorship programme will assist in providing the support you need as you navigate all the complexities this experience is likely to present. I’d also like to thank all the mentors within the programme for giving their time and skills. Should you be interested in becoming a mentor kindly contact Annalie, who is always on the lookout for new participants. Mental health and resilience remain one of the top priorities and this month several initiatives in this area are starting to take shape. The long-awaited Lincoln Institute and Mentorvet scholarship programme will resume in February. A total of 65 veterinarians from South Africa have been selected to participate. I would like to congratulate all the selected participants and encourage those not selected in this year’s programme to re-apply when the opportunity presents itself again. The competencies that will be developed are lifelong and essential for the sustainability of the profession. We are also excited to announce that we have received 14 names that indicated their willingness to serve on the newly established SAVA Mental Health Committee. The names of these committee members will be released in due course. Lastly on “mind-matters”, SAVA has been approached by an organisation known as Mind Matters Internation, to assist in developing an initiative called "Vital Transitions" which will focus on supporting the mental health of individuals as they move from veterinary school into practice. This programme consists of a series of events which will be regionally driven. The kick off-event will likely be a 1-day online conference inclusive of all the regions, then a series of regional meetings followed by another all-inclusive event. This is an exciting development that will strengthen our initiatives in this area. At the IVOC meeting held in January 2025, discussions were held amongst the member countries on various initiatives including veterinary education, support models for rural practices/ practitioners, retention strategies for veterinarians in specialist fields and general advocacy initiatives. Some innovative ideas were shared. During this period SAVA also continued to advocate for the availability of safe and efficacious medications to the profession and engage with the Department of Agriculture on various matters. The year 2025 is an election year for the SAVC. Once again, the call to stand for election, vote for suitable candidates and serve the veterinary and para-veterinary professions will be made. Let us be on the lookout for communication and actively participate in the process to ensure that the profession is equitably represented and that the activities of the SAVC align with our intentions for the profession for the benefit of the country. January and February are membership renewal months. I’d like to encourage all of us to continue supporting the organisation and its work, actively participate in initiatives, groups and branches and remain strong advocates for the profession. Stay blessed! v Ziyanda From the President Dear members, Alignment!
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Vetnews | Februarie 2025 4 « BACK TO CONTENTS And with a wink, we are in the second month of 2025. “Skouer aan die wiel” is what we would say in Afrikaans (direct translation: Shoulder to wheel). A saying that means now we are in for the hard work. January was a bit of a blur for me as we only returned from the UK and Belgium on the 19th and it took a couple of days to acclimatize and for my brain to join my body again. Welcome to the veterinarians new to the Association. In the magazine is more information on what SAVA does for you. For the long-standing members, have a look at it, there may be something new you have not noticed before. What will 2025 bring? Bright-eyed and bushy-tailed we enter the unknown. February will see the continuation of the planet dance. An astronomical feast, even though it is not that simple to see with the naked eye. We are still trying to take some clear photos. The Brown veined Whites (the masses of white butterflies) are at the height of their migration from the Kalahari to Mozambique. Research has shown an astonishing number of between 80,000 and 150,000 butterflies per hour through Gauteng. Looking around and up makes a lot of stuff more tolerable. This month the focus is on aquatic animals. Not a field many veterinarians will be in, but very interesting nonetheless. Comparing just anaesthetic between land and water animals is fascinating as the challenges are so different. It makes for an interesting read. February is also the month of the great Valentine. Remember your student days and get a little silly. Watch the stars, plant a tree, or walk the dog or cat (I would not recommend your fish unless you make special provisions. I did not realise that January was traditionally “Walk your dog” month – which seems to concur well with New Year resolutions. But I think there should be no discrimination – walk any pet you have (even your spouse). Visit your parents or grandparents (if you are still lucky enough to have some), your kids, or your neighbours or colleagues. Visit any-one. My wish is for a great second month of 2025 and the last official month of Summer. Do something scary, visit an unknown place or try a new hobby. The 310 days of January are over and February is a short one. Andriette v From the Editor Editor’s notes / Redakteurs notas Email: assistant@sava.co.za ADVERTISE IN VETNEWS MAGAZINE
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Vetnews | Februarie 2025 8 « BACK TO CONTENTS Cardiopulmonary adaptations of a diving marine mammal, the bottlenose dolphin: Physiology during anesthesia Abstract Diving marine mammals are a diverse group of semi-to completely aquatic species. Some species are targets of conservation and rehabilitation efforts; other populations are permanently housed under human care and may contribute to clinical and biomedical investigations. Veterinary medical care for species under human care, at times, may necessitate the use of general anesthesia for diagnostic and surgical indications. However, the unique physiologic and anatomic adaptations of one representative diving marine mammal, the bottlenose dolphin, present several challenges in providing ventilatory and cardiovascular support to maintain adequate organ perfusion under general anesthesia. The goal of this review is to highlight the unique cardiopulmonary adaptations of the completely aquatic bottlenose dolphin (Tursiops truncatus) and to identify knowledge gaps in our understanding of how those adaptations influence their physiology and pose potential challenges for sedation and anesthesia of these mammals. 1. INTRODUCTION Approximately 50–55 million years ago, a terrestrial artiodactyl similar to a small deer made the transition from land to water (Thewissen et al., 2009, 2007). Fossil records suggest that this ancestor of cetaceans became more amphibious over millennia until it became fully aquatic. Cetacea is the mammalian infraorder that includes whales, dolphins and porpoises. Carolina R. Le-Bert, Gordon S. Mitchell, Leah R. Reznikov Study objective(s) No Age(years) Weight range (kg) Pre-medication agent(s) Effect of halothane anesthesia on hepatic damage during auditory research 6 (F = 3, M = 3) N/A N/A N/A Bispectral index monitor to detect interhemispheric asymmetry 3 (F = 1, M = 2) N/A 212–263 Diazepam, 0.15 mg/kg, PO (n = 1) Anesthesia induction and maintenance with thiopental and halothane 10 5 N/A N/A N/A N/A N/A N/A Surgical approach to the dolphin ear 4 N/A N/A Atropine, 0.02 mg/kg, Hemodynamic and coronary angiographic studies in the dolphin 4 N/A 80 - 114 N/A Return of sound production following anesthetic recovery 10 (F = 4, M = 6) 8–46 (mean 32.4) N/A Midazolam, 0.08–0.1 mg/kg, IM Meperidine, 0.1–0.2 mg/kg, IM Apneustic anesthesia ventilation on pulmonary function 9 (F = 3, M = 6) 10–42 (mean 32) 141–292 Diazepam, 0.08–0.30 mg/kg, PO (n = 2) Midazolam, 0.08–0.1 mg/kg, IM Meperidine, 0.1–0.2 mg/kg, IM Plasma propofol concentrations in dolphins 6 12–27 (mean unk) N/A Diazepam, PO Midazolam, IM TABLE 1 Summary of general anesthesia performed during anatomic and physiologic studies of dolphins (Tursiops spp.)
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
Vetnews | Februarie 2025 10 « BACK TO CONTENTS apneustic plateau control unit, created to mimic the breath-holding apneustic breathing pattern of cetaceans. Apneustic plateau ventilation, as coined by Ridgway and McCormick, enabled rapid lung inflation with an inspiratory breath hold at approximately 20– 24 mmHg pressure for 15–30 s, followed by airway pressure release, and rapid re-inflation (Ridgway et al., 1974; Ridgway & McCormick, 1971, 1967). Early ventilation practices using conventional modes of ventilation would result in decreasing trends towards hypoxemia due to hypoventilation (Ridgway et al., 1974). Thus, apneustic plateau ventilation was the standardized approach for mechanical ventilation of dolphins. Anesthetic practices in the 60s and 70s evaluated the use of a low solubility anesthetic gas, nitrous oxide, for maintaining a surgical plane of anesthesia. This minimally potent inhalational anesthetic was often combined with a neuromuscular blocking agent (succinylcholine) and a parenteral barbiturate (thiopental) in dolphins. However, a mixed gas anesthetic protocol of 60% nitrous oxide with 40% oxygen did not result in a surgical plane of anesthesia. In one study, an increase to 80% nitrous oxide resulted in lost reflexes and complete unconsciousness following an initial period of hyperexcitability (Ridgway & McCormick, 1971). In a separate study, persistent reflexes and visual tracking at the same concentration of nitrous gas mixture was reported (Ridgway & McCormick, 1967). Further, at 80% nitrous oxide, hypoxemia and cyanosis of the mucus membranes were observed. The combination of continued presence of consciousness and inadequate oxygenation at high inspired nitrous oxide concentrations, led Ridgway and colleagues to cite the nitrous gas mixture as inadequate for major surgery in dolphins, especially as a sole anesthetic agent (Ridgway & McCormick, 1967). Early hemodynamic studies in these anesthetized dolphins provided insights into cardiovascular function under general anesthesia. Mean arterial pressures in healthy dolphins on halothane gas anesthesia averaged 115 mmHg (normal reported as 120–140 mmHg) (Ridgway & McCormick, 1971). Dolphins on nitrous oxide-oxygen gas anesthesia ranged between 122 and 142 mmHg (Sommer et al., 1968). Ridgway also observed that the normal, respiratory sinus arrhythmia (RSA) observed in the conscious, nonanesthetized dolphin transitioned to a normal sinus rhythm, with heart rates between 80 and 160 bpm, after thiopental (15–25 mg/ kg) administration (Ridgway et al., 1974; Ridgway & McCormick, 1971, 1967). While Ridgway published on observational aspects of clinical anesthesia in dolphins, few comprehensive and controlled physiologic studies of anesthetized dolphins have since been conducted (McCormick, 1969; Sommer et al., 1968). Most reports are limited to single case descriptions that document individual dolphins (Tursiops spp.) recovering from surgical or diagnostic procedures, rather than controlled pharmacokinetic or physiologic studies on the effects of ventilation and anesthetics agents (Table 2) (Bailey, 2021; Doescher et al., 2018; Dover et al., 1999; Lee et al., 2019; Lindemann et al., 2023; Meegan et al., 2015, 2016; Meegan, Miller, et al., 2021; Ridgway, 2002; Russell et al., 2021; Schmitt et al., 2014; Tamura et al., 2017). The paucity of comprehensive, controlled anesthetic studies in bottlenose dolphins remain a hurdle in our understanding of the physiology of anesthesia in this species. 3. MECHANISMS AND CURRENT APPROACHES TO DOLPHIN ANESTHESIA Anesthetic and analgesic agents modulate the central nervous system (CNS) via activity on gamma-aminobutyric acid type A (GABAA), N-methyl D-aspartate (NMDA), adrenergic alpha-2, and opioid receptors. Ion channels, such as the family of neuronal hyperpolarization-activated cyclic nucleotide-gated (HCM) and two-pore domain potassium (K2P) channels, are also known targets for anesthetic agents (Cascella et al., 2020; Pavel et al., 2020). For example, the excitatory glutamate NMDA receptor is associated with neuropathic pain and is antagonized by dissociative anesthetics like ketamine, tiletamine, and phencyclidine. The GABAA receptors are targets for the CNS inhibitory effects of propofol, etomidate, alfaxalone, barbiturates, and benzodiazepines. Alpha-2 adrenergic agonists, such as dexmedetomidine, tizanidine, and clonidine, produce effects centrally within the locus coeruleus (sedation) and dorsal horn (pain), as well as peripherally to modulate blood pressure, cardiac output, and insulin release from the pancreatic beta cells (Giovannitti Jr et al., 2015). Opioids (morphine, codeine, methadone, tramadol, meperidine, butorphanol, buprenorphine) exert their effects at central and peripheral mu, kappa, and delta opioid receptors and can cause hypotension and sinus bradycardia through depression of sinoatrial node activity. However, the most notable and often critical effects of opioids are seen as centrally-mediated depression of the respiratory centers, whereby hypoventilation can lead to life-threatening hypercapnia. Volatile anesthetics, like sevoflurane, isoflurane, and desflurane, depress the response to carbon dioxide in a dose-dependent fashion and may cause sedation, in part, by inhibiting cholinergic neurotransmission in regions of the brain that regulate arousal (Vacas et al., 2013). With these mechanisms in mind, current approaches to anesthesia of bottlenose dolphins may present several physiologic challenges for the anesthetist. The use of drugs causing and contributing to cardiopulmonary depression, as is also seen in large terrestrial mammals, is an undesired consequence leading to a variety of anesthesia-associated co-morbidities (Bukoski et al., 2022; GozaloMarcilla et al., 2014; Menzies et al., 2016; Sage et al., 2018). Currently, no literature exists on the cardiopulmonary impacts of anesthesia protocols on dolphins. Per the experience of the authors, cardiopulmonary derangements, such as hypoventilation, ventilation-perfusion mismatch, decreased functional residual capacity (FRC), vasodilation, and depression of cardiac contractility are often observed in anesthetized dolphins using commonly accepted anesthetic drugs (e.g., opioids, propofol, benzodiazepines, and inhalation anesthetics) and protocols (e.g., various combinations of ventilation methods and drug selection). These effects can often lead to hypoxemia, hypercapnia, hypotension, and decreased cardiac output (Berry, 2015; Haskins, 2015; Steffey et al., 2015). If not properly mitigated, these effects can impair organ perfusion, reduce oxygen delivery, and predispose the dolphin to organ injury and myopathic conditions (Bailey, 2021; Dold & Ridgway, 2014; Haulena & Schmitt, 2018). For example, decreased work of breathing and subsequent respiratory depression is a characteristic of dolphin sedation (benzodiazepines and opioids) that often demands respiratory support in the form of mechanical ventilation (Dold & Ridgway, 2014; Ridgway & McCormick, 1971, 1967). The use Leading Article
Vetnuus | February 2025 11 Leading Article Clinical indication Age (years) Sex Weight (kg) Premedication agent(s) Induction agent(s) Maintenance agent(s) MAP range (mmHg) Reversal agent(s) Reference Cerebral spinal fluid sampling 5 F 106 Diazepam 0.28 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 93-122 Flumazenil 0.01 mg/kg IM Russell et al. 2021;Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 2 mg/kg IV Flumazenil 0.01 mg/kg IV Ventral cervical abscess surgical debridement 22 F 174 Midazolam 0.07 mg/kg IM Midazolam 0.04 mg/ kg IV Sevoflurane 44-55 Flumazenil 0.04 mg/kg IV Lee et al. 2019;Meeganet al. 2015;Bailey 2021 Meperidine 0.5 mg/kg IM Propofol 2 mg/kg IV Naloxone 0.02 mg/kg IV Naltrexone 0.05 mg/kg IV Renal biopsy laparoscopy 27 F 150 Diazepam 0.27 mg/kg PO Propofol 3.5 mg/ kg IV Isoflurane N/A Flumazenil 0.001 mg/kg IM Doveret al. 1999;Bailey 2021 Atropine 0.02 mg/kg IM Flumazenil 0.002 mg/kg IV Electroencephalography N/A M 140 N/A Sodium thiopental IV Halothane N/A Ridgway 2002 Lithotripsy 39 F 175 Midazolam 0.07 mg/kg IM Midazolam 0.06 mg/ kg IV Sevoflurane 57-117 Flumazenil 0.024 mg/kg IV Bailey 2021 Propofol 3.6 mg/ kg IV Partial glossectomy 24 F 206 Diazepam 0.24 mg/kg PO Midazolam 0.024 mg/ kg IV Sevoflurane 63-81 Flumazenil 0.017 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 4 mg/kg IV Flumazenil 0.01 mg/kg IM Corneal scleral mass 17 M 184.5 Diazepam 0.22 mg/kg PO Midazolam 0.027 mg/ kg IV Sevoflurane N/A Flumazenil 0.01 mg/kg IV Bailey 2021 Midazolam 0.054 mg/ kg IM Propofol 2.87 mg/ kg IV Edrophonium 0.5 mg/kg IV Atracurium 0.1 mg/ kg IV Mandibular sequestrum debridement 18 M 220.5 Diazepam 0.18 mg/kg PO Midazolam 0.023 mg/ kg IV Sevoflurane 25-35 Flumazenil 0.026 mg/kg IV Bailey 2021
Vetnews | Februarie 2025 12 « BACK TO CONTENTS Clinical indication Age (years) Sex Weight (kg) Premedication agent(s) Induction agent(s) Maintenance agent(s) MAP range (mmHg) Reversal agent(s) Reference Midazolam 0.05 mg/kg IM Propofol 1.5 mg/ kg IV Naloxone 0.02 mg/kg IV Naltrexone 0.05 mg/kg IV Glossectomy 44 M 215.5 Diazepam 0.23 mg/kg PO Propofol 4 mg/kg IV Sevoflurane 44-87 Flumazenil 0.019 mg/kg IV Doescher et al. 2018;Bailey 2021 Midazolam 0.08 mg/kg IM Partial glossectomy 35 F 245 Diazepam 0.25 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane N/A Flumazenil 0.02 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 2 mg/kg IV Partial glossectomy 27 F 225 Diazepam 0.25 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 98-120 Flumazenil 0.022 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 1.15 mg/kg IV Atropine 0.02 mg/kg IM Partial glossectomy 20 F 190 Diazepam 0.25 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 33-65 Flumazenil 0.025 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 2.1 mg/kg IV Lymphadenectomy 49 M 140 Midazolam 0.2 mg/kg IM Midazolam 0.035 mg/ kg IV Sevoflurane 24-53 Flumazenil 0.021 mg/kg IV Bailey 2021 Propofol 1.5 mg/kg IV Naloxone 0.04 mg/ kg IV Gastroscopy for foreign body retrieval 12 M 117 Midazolam 0.1 mg/kg IM Midazolam 0.042 mg/ kg IV Sevoflurane 76-119 Flumazenil 0.016 mg/kg IV Bailey 2021 Propofol 2.14 mg/kg IV Naloxone 0.017 mg/kg IV Atracurium 0.2 mg/kg IV Naltrexone 0.2 mg/kg IV Partial glossectomy 46 F 210 Diazepam 0.24 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane N/A Flumazenil 0.03 mg/kg IV Bailey 2021 Midazolam 0.02 mg/kg IM Propofol 2.95 mg/kg IV Oral surgery ophthalmic examination 38 F 187.5 Midazolam 0.08 mg/kg IM Midazolam 0.02 mg/ kg IV Sevoflurane 73-96 Flumazenil 0.015 mg/kg IV Bailey 2021 Meperidine 0.1 mg/kg IM Propofol 2.29 mg/kg IV Naloxone 0.02 mg/kg IV Leading Article Cardiopulmonary adaptations of a diving marine mammal, the bottlenose dolphin.... <<<11
Vetnuus | February 2025 13 Clinical indication Age (years) Sex Weight (kg) Premedication agent(s) Induction agent(s) Maintenance agent(s) MAP range (mmHg) Reversal agent(s) Reference Ophthalmic surgery 22 M 171 Diazepam 0.1 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 60-115 Flumazenil 0.018 mg/kg IV Bailey 2021 Midazolam 0.09 mg/kg IM Propofol 3 mg/kg IV Naloxone 0.03 mg/ kg IV Meperidine 0.2 mg/kg IM Bronchoscopic dilatation 8 M 196 Diazepam 0.2 mg/kg PO Midazolam 0.03 mg/ kg IV Sevoflurane 62-84 Flumazenil 0.02 mg/kg IV Bailey 2021; Meegan Ardente et al. 2021 Midazolam 0.08 mg/kg IM Propofol 3 mg/kg IV Naloxone 0.02 mg/kg IV Meperidine 0.1 mg/kg IM Partial glossectomy 16 M 181 Diazepam 0.25 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 39-42 Flumazenil 0.022 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 1.65 mg/kg IV Tail abscess surgical debridement 14 F1 160 Midazolam 0.075 mg/kg IM Propofol 1.4 mg/kg IV Sevoflurane Indirect: 36-49 Flumazenil 0.015 mg/kg IV Tamura et al. 2017 Butorphanol 0.05 mg/kg IM Doxapram 1 mg/kg IV 14 F1 160 Midazolam 0.075 mg/kg IM Propofol 3.7 mg/kg IV Sevoflurane Indirect: 25-95 Flumazenil 0.015 mg/kg IV Tamura et al. 2017 Butorphanol 0.05 mg/kg IM Direct: 24 Doxapram 1 mg/kg IV Superficial keratectomy and cryosurgery of limbal melanoma 7.5 F2 175 Diazepam 0.26 mg/kg PO Midazolam 0.05 mg/ kg IV Sevoflurane N/A Flumazenil 0.025 mg/kg IV Bailey 2021;Schmitt et al. 2014 Propofol 5.48 mg/kg IV Flumazenil 0.025 mg/kg IM 10 F2 185 Butorphanol 0.11 mg/kg IM Midazolam 0.027 mg/ kg IV Sevoflurane N/A Flumazenil 0.032 mg/kg IV Bailey 2021 Midazolam 0.081 mg/kg IM Propofol 2.4 mg/kg IV Edrophonium 0.5 mg/kg IV Atracurium 0.1 mg/kg IV Dental surgery 36 M1 263 Midazolam 0.08 mg/kg IM Midazolam 0.02 mg/ kg IV Sevoflurane 31-67 Flumazenil 0.01 mg/kg IV Bailey 2021; Meegan et al. 2016 Propofol 3.8 mg/kg IV Leading Article >>>14 Cardiopulmonary adaptations of a diving marine mammal, the bottlenose dolphin.... <<<12
Vetnews | Februarie 2025 14 « BACK TO CONTENTS Leading Article Clinical indication Age (years) Sex Weight (kg) Premedication agent(s) Induction agent(s) Maintenance agent(s) MAP range (mmHg) Reversal agent(s) Reference 37 M1 241 Midazolam 0.08 mg/kg IM Midazolam 0.02 mg/ kg IV Sevoflurane 29-75 Flumazenil 0.02 mg/kg IV Bailey 2021 Propofol 4.3 mg/kg IV Naloxone 0.01 mg/kg IV Meperidine 0.4 mg/kg IM Naltrexone 0.05 mg/kg IV 38 M1 234 Midazolam 0.08 mg/kg IM Midazolam 0.03 mg/ kg IV Sevoflurane 73-84 Flumazenil 0.012 mg/kg IV Bailey 2021 Propofol 5.5 mg/kg IV Naltrexone 0.05 mg/kg IV Meperidine 0.25 mg/kg IM Corneal mass excision 15 F3 180 Diazepam 0.25 mg/kg PO Propofol 2.78 mg/kg IV Sevoflurane 67-91 Flumazenil 0.014 mg/kg IV Bailey 2021 Midazolam 0.08 mg/kg IM Atracurium 0.1 mg/kg IV Edrophonium 0.5 mg/kg IV 16 F3 190 Diazepam 0.21 mg/kg PO Midazolam 0.026 mg/ kg IV Sevoflurane N/A Flumazenil 0.026 mg/kg IV Bailey 2021 Midazolam 0.05 mg/kg IM Propofol 2.87 mg/kg IV Edrophonium 0.53 mg/kg IV Atracurium 0.1 mg/kg IV Bronchoscopy 16 M2 195 Diazepam 0.1 mg/kg PO Propofol 4 mg/kg IV Sevoflurane 50-64 Flumazenil 0.15 mg/kg IV Bailey 2021 Midazolam 0.08 mg/kg IM Meperidine 0.25 mg/kg IM Naloxone 0.01 mg/kg IV Naltrexone 0.05 mg/kg IV Ophthalmic surgery 17 M2 202 Diazepam 0.2 mg/kg PO Midazolam 0.03 mg/ kg IV Sevoflurane N/A Flumazenil 0.01 mg/kg IV Bailey 2021 Midazolam 0.07 mg/kg IM Propofol 2.23 mg/kg IV Naloxone 0.01 mg/kg IV Meperidine 0.25 mg/kg IM cisAtracurium 0.1 mg/kg IV Naltrexone 0.05 mg/kg IV Partial glossectomy 37 F4 256 Diazepam 0.2 mg/kg PO Midazolam 0.02 mg/ kg IV Sevoflurane 66-86 Flumazenil 0.03 mg/kg IV Bailey 2021 Tramadol 1.0 mg/kg PO Propofol 3.05 mg/kg IV Naloxone 0.023 mg/kg IV Corneal repair 38 F4 243 Diazepam 0.25 mg/kg PO Propofol 1.0 mg/kg IV Sevoflurane Flumazenil 0.037 mg/kg IV Bailey 2021 Midazolam 0.14 mg/kg IM Atracurium 0.3 mg/kg IV Exploratory laparoscopy 28 M N/A Ketamine 1 mg/kg IM Midazolam 0.02 mg/ kg IV Sevoflurane N/A N/A Lindemann et al. 2023 Midazolam 0.02 mg/kg IM Propofol 0.6 mg/kg I TABLE 2 Summary of single case reports of successful general anesthesia and recovery in dolphins (Tursiops spp.)
Vetnuus | February 2025 15 Leading Article of propofol for induction and inhalation anesthetics for anesthesia maintenance may cause vasodilation and could lead to depressed cardiac contractility (Berry, 2015). Together, the reduced oxygen delivery to muscles could promote rhabdomyolysis, or the breakdown of skeletal muscle fibers, and lead to kidney injury from the breakdown products (e.g., myoglobin) (Bailey et al., 2012). Thus, there is a need to understand the physiologic impactsof anesthesia in dolphins, as well as develop strategies to reduce anesthesia-associated morbidities. As noted by Ridgway and colleagues, the out-of- water induction of anesthesia abates all spontaneousventilation in dolphins (Bailey et al., 2022; McCormick & Ridgway, 2018). Mechanical ventilation is, therefore, required to prevent the pathophysiologic consequences of hypoventilation. The most employed mechanical ventilation approach in veterinary species, controlled or conventional mechanical ventilation, mirrors the normal respiratory pattern of terrestrial mammals. Dolphins, however, have an inspiratory breath-hold respiratory phenotype with significant heart rate variation during each inspiratory-to- expiratory cycle (RSA) (Fahlman et al., 2020; Le-Bert et al., 2024; McCormick, 1969). This cardiopulmonary coupling strategy may improve gas exchange in the conscious diving dolphin; however, it is completely abolished with mechanical ventilation (Fahlman et al., 2020). The uncoupling effect on efficient respiratory gas exchange under anesthesia is unknown and may be of consequence. While mechanical ventilation is a critical feature of dolphin anesthesia, it can also promote alveolar collapse (atelectasis), leading to ventilation-perfusion mismatching. While Nagel, Ridgway, and colleagues were able to mechanically mimic dolphin breathing using apneustic plateau ventilation (APV) through the modification of existing large animal ventilators, the availability of this mechanical ventilation strategy to dolphin veterinarians, as well as an understanding of its effect on respiratory gas exchange under anesthesia, are lacking. A ventilation strategy that maintains airway pressure above functional residual capacity (e.g., the point in the breathing cycle where alveoli are more prone to collapse) by decreasing lung volume and pressure from an elevated plateau pressure to an airway pressure at or slightly above functional residual capacity was recently described and tested on pigs, horses, and dolphins (Bratzke et al., 1998; Bukoski et al., 2022, 2024; Le-Bert et al., 2024). In these studies, the authors compared the cardiopulmonary effects of apneustic anesthesia ventilation (AAV) and conventional mechanical ventilation (CMV) in 12 adult pigs, 10 healthy adult horses, and 10 healthy adult bottlenose dolphins. In the horse and pig studies, the authors found that AAV resulted in significantly higher respiratory system dynamic compliance (change in lung volume over the change in pleural pressure) and lower venous admixture, or physiologic shunt (Bukoski et al., 2022, 2024). In dolphins, AAV resulted in higher arterial oxygen tension and reduced alveolar dead space ventilation (Le-Bert et al., 2024). Thus, this ventilation strategy demonstrated some physiologic advantages for cardiopulmonary function while mechanically ventilating anesthetized dolphins and warrants further investigation. Another significant challenge to the physiology of anesthesia in dolphins is the impact of gravity on a species that evolved in a buoyant ocean environment (Le-Bert et al., 2024). When dolphins are removed from the neutrally buoyant environment, as is often necessary for medical and surgical procedures, the influence of gravity on hemodynamic variables may become an important factor (Figure 1). Resulting pressure gradients across dolphin tissues could contribute to whole body fluid shifts and blood flow redistribution when out of water for anesthetic procedures. Gravityinduced hemodynamic shifts will be discussed in the next section and should be considered and mitigated in anesthetized dolphins when possible. 4.CARDIOPULMONARY ADAPTATIONS RELEVANT TO ANESTHESIA IN BOTTLENOSE DOLPHINS While cetaceans evolved for life in diverse aquatic habitats, all cetacean species rely on intermittent surfacing to breathe air. Consequently, prolonged intervals of breath-holding required for locomotion and foraging impact respiratory gas exchange and metabolism (Noren et al., 2012). As such, cetaceans developed specialized anatomic characteristics and physiologic adaptations which must be considered during anesthesia. Here, we expand upon select cardiovascular and pulmonary adaptations to diving and breath-holding activities and how these adaptations may influence dolphin responses to anesthetic agents. FIGURE 1 A significant challenge to general anesthesia in dolphins is the impact of gravity on a species that evolved in a buoyant ocean environment. For this reason, Ridgway would perform surgical approaches to the dolphin ear in a partially suspended state—a surgical table-tank. The water in the surgical table-tank was also heated to assist with thermoregulation of core body temperature (Image courtesy of the U.S. Navy's Marine Mammal Program). >>>16
Vetnews | Februarie 2025 16 « BACK TO CONTENTS Leading Article 4.1 Cardiovascular system adaptations Cetaceans exhibit unique cardiovascular system morphology and physiology to support the circulatory and metabolic requirements of a diving lifestyle. For example, a dorsal-ventral flattening of the four-chambered heart limits the impact of chest wall compression on ventricular filling (preload) during a dive (Ochrymowych & Lambertsen, 1984). The cetacean heart is believed to have a Purkinje fiber distribution similar to terrestrial ungulates, also referred to as a Category B, or Type 2, ventricular depolarization pattern (Calloe, 2019; Hamlin, 1970; Hamlin & Smith, 1965; Harms et al., 2013; Kinoshita et al., 2023). These larger Purkinje fibers are believed to increase signal conduction velocity from the atrioventricular node to the ventricular myocardium and may benefit the observed rapid heart rate transitions from a diving bradycardia to a resurfacing tachycardia (Storlund et al., 2021). Conversely, a recent histologic study of the dolphin heart demonstrated the Purkinje fibers actually run just below the endocardium, as seen in humans (Category A ventricular depolarization pattern), and do not extend through the myocardium as is typical of terrestrial ungulates (Kinoshita et al., 2023). In a meta-analysis comparing ECG morphology of 50 species of terrestrial mammals and 19 species of marine mammals, marine mammal species exhibited slower atrial (19% longer P-wave) and ventricular depolarization (24% longer QRS interval), and faster ventricular repolarization (21% shorter QT interval) than terrestrial mammals (Storlund et al., 2021). These electrophysiologic features would suggest an effect of the larger myocardial mass of dolphins influencing the duration of the electrical signal conduction (Storlund et al., 2021). These ECG features are relevant to the physiologic monitoring of both awake and anesthetized dolphins and should, therefore, be considered in the management of perfusion states. More research into the anatomic and physiologic differences contributing to the ventricular activation pattern of dolphins and the potential impact on circulation under general anesthesia is warranted. The vascular anatomical features of the dolphin are also important when considering the anesthetic effects on dolphin physiology. Cetacean veins and arteries are extremely specialized with respect to circulation, hemodynamics, blood storage, oxygen transport, and thermoregulation. In cetacean appendages (pectoral flippers, tail fluke, dorsal fin), arteries and veins form a complex of vessels known as periarterial venous retia (Meagher et al., 2002). Retia function as counter-current heat exchangers to support thermoregulation (core body temperature regulation) in the thermally conductive aquatic environment. Highly specialized networks of elaborate vessels, known as retia mirabilia (“wonderful nets”), around the brain and spinal cord (cranial and spinal rete mirabilis), cervicothoracic vertebrae (cervical and thoracospinal retia mirabilia), gonads and eyes (cranial and ophthalmic rete mirabilis), are also key cardiovascular adaptations in cetaceans (Ballarin et al., 2018; Bonato et al., 2019; Costidis, 2012; Cozzi et al., 2017; Lillie et al., 2022; Rommel et al., 1992; Rowlands et al., 2021). These complex vascular structures consist of a single artery with many smaller branching vessels suspended among numerous small veins, giving the appearance of a vascular net or meshwork. They are the major site of blood storage in cetaceans (Bonato et al., 2019; Cozzi et al., 2017). Rete mirabilia may function in maintaining arterial blood pressure and providing adequate cerebral perfusion independent from the peripheral thermoregulatory periarterial venous retia (Lillie et al., 2022; Rowlands et al., 2021). The elaborate morphology of the retial system within the cetacean skull and vertebral canal, and its vascular connections to thoracic and abdominal cavities, likely enables hemodynamic adjustments necessary for diving (Bonato et al., 2019; Nagel et al., 1968; Rowlands et al., 2021). In the natural, neutrally buoyant condition, the lack of pressure gradients across dolphin tissues may necessitate dependence on non-cardiac pumps to adequately circulate blood throughout the body, for example, via the dorsoventral fluke oscillations of locomotion (Lillie et al., 2022). Aside from complex vascular retia, true veins are another interesting morphologic feature of the circulatory system in dolphins. Most dolphin veins are valve-less, which implies the ability for bidirectional blood flow and the reliance on non-cardiac pumps, such as muscles of locomotion and retia mirabilia, to promote adequate tissue perfusion (Costidis, 2012; Harrison & Tomlinson, 1956). This feature may be particularly important when dolphins are anesthetically immobilized, rendering non-cardiac pumps temporarily dysfunctional. In addition to anatomical cardiovascular adaptations advantageous for a diving lifestyle, pelagic (deep-diving) cetaceans rely on intrinsic oxygen stores via increased cytoglobin (neural), as well as increased blood volumes, to tolerate prolonged dives (Dolar et al., 1999; Noren & Williams, 2000). These features enable continued aerobic metabolism despite prolonged apnea at depth (Ponganis et al., 2011). Myoglobin concentration is 10–30 fold higher in the skeletal muscle of aquatic diving mammals versus terrestrial mammals (Kooyman et al., 1981). Increased myoglobin allows for increased oxygen storage, with subsequent release during breathhold underwater exercise. In general, as diving capacity increases across cetacean taxa and ecotypes, skeletal muscle myoglobin concentrations, blood volume, and hemoglobin also increase (Butler & Jones, 1997; Fago et al., 2017; Horvath et al., 1968; Noren & Williams, 2000; Remington et al., 2007; Taboy et al., 2000). Hemoglobin also adds to whole body oxygen stores and is directly proportional to total blood volume (Snyder, 1983). The shallowdiving bottlenose dolphin, however, does not exhibit increases in red blood cell volume, hemoglobin, or myoglobin, as is measured in the deep-diving cetaceans (Fahlman et al., 2018). Blood volume in this coastal species is closer to terrestrial mammals at ~7.1% of body mass (Johnson et al., 2009; Ridgway & Johnston, 1966). Early studies found that hemoglobin has a higher affinity for oxygen in the small, shallow-diving bottlenose dolphin compared to the larger, deep-diving species (Snyder, 1983). This observation was believed to facilitate oxygen extraction from the lungs during short dives, as well as facilitating oxygen off-loading to the tissues during deep dives when lungs are collapsed. However, more recent evidence suggests diving mammals have hemoglobin oxygenation properties similar to terrestrial mammals, and that previously observed differences in the oxy-hemoglobin dissociation curve more likely reflect differences in red blood cell 2,3-diphosphoglycerate (DPG) concentration (Fago et al., 2017).
Vetnuus | February 2025 17 Leading Article Lastly, there is evidence of adaptations in neural mechanisms of cardiovascular control. Specifically, alpha-adrenergic 2B receptors in another toothed whale, the sperm whale, exhibit protein sequence differences in the polyglutamate acid domain, which likely affect agonist-induced phosphorylation and receptor activation (Madsen et al., 2002; Small et al., 2001). Relevant to the pharmacology of anesthetic agents, this catecholamine receptor is concentrated in the spinal cord, kidneys and vascular endothelium, and can influence sedation, analgesia, muscle relaxation, bradycardia and systemic vascular resistance. Given these sequence differences of alpha 2B adrenergic receptors, sympathomimetic drugs including alpha 2 adrenergic receptor agonists and antagonists likely exhibit differential binding affinities which may, in turn, impact cardiovascular function in anesthetized dolphins. 4.1.1 Cardiovascular plasticity of the diving dolphin The mammalian dive response consists of several key events that preserve intrinsic oxygen stores and prevent asphyxia, particularly in vital organs such as the heart and brain (Panneton, 2013). First, activation of facial trigeminal nerve reflexes during submersion induces a parasympathetic response and acetylcholine release (Berk et al., 1991; Ponganis, 2019). Acetylcholine activates heart muscarinic receptors, decreasing heart rate (bradycardia). Bradycardia lowers the chronotropic state of the heart, thereby reducing oxygen consumption, conserving oxygen stores and mitochondrial energy production. Since cardiac output is the product of heart rate and stroke volume (volume of blood ejected per heartbeat), a decrease in heart rate (bradycardia) decreases cardiac output, at least if stroke volume is unchanged. Decreased cardiac output impacts tissue oxygen delivery and thus, perfusion, and limits dive duration. Bottlenose dolphins decrease heart rate from ~101– 111 bpm to ~20–30 bpm within 1 min of water submergence (Houser, Dankiewicz-Talmadge, et al., 2010; Williams et al., 2015, 1993). Williams and colleagues demonstrated that dive depth and exercise intensity alter the extent of bradycardia in diving dolphins (Williams et al., 2015). In that same study, dolphins at diving depth exhibited ~1.7–3.7 fold increase in heart rate over gliding values during exercise (swimming). Dive depth and duration were important modulators of that exercise response. Thus, Williams and colleagues postulated that the interplay between sympathetic and parasympathetic systems (autonomic conflict) of breath-hold exercising at depth was responsible for the observed heart rate variability and cardiac anomalies. However, Ponganis and colleagues presented an alternative interpretation of the exercise response in diving marine mammals, de-emphasizing the concept of autonomic conflict and proposing that instead: (1) sympathetic activation is elevated at dives even without exercise, as evidenced by maximal vasoconstriction, (2) parasympathetic cardiac vagal tone dominates over sympathetic cardiac tone in diving animals (as evidenced by bradycardia), (3) exercise modulation of heart rate during dives primarily involves reduction in parasympathetic tone versus increased sympathetic tone and, finally, (4) benign arrhythmias are common in marine mammals (Ponganis et al., 2017). Hydrostatic pressure increases with dive depth and, thus, exerts increasing intrathoracic pressures on the dolphin cardiopulmonary system while diving. Changes in hydrostatic pressure while diving are believed to modulate chronotropic and inotropic function of the heart through its influence on pulmonary volumesreceptors, and changes in blood gas tensions (Williams et al., 2015). Mechanical ventilation during anesthesia also increases intrathoracic pressure and can negatively impact cardiac output (Mahmood & Pinsky, 2018). In 1968, Sommer and colleagues measured stroke volume (0.4–0.8 mL/kg) and cardiac output (47–105 mL/min/ kg) in four dolphins under anesthesia, noting the likely influence of mechanical ventilation and out-of- water experimental conditions on hemodynamic variables (Sommer et al., 1968). More recently, the availability of non-invasive transthoracic and transesophageal echocardiography has allowed for in-water cardiovascular evaluation of awake, spontaneously ventilating dolphins (Chetboul et al., 2012; Linnehan et al., 2021; Miedler et al., 2015; Sklansky et al., 2006). In one study, cardiac output was determined by calculating the stroke volume from the integrated blood flow velocity and the aortic cross-sectional area at the level of the aortic valve using transthoracic echocardiography (Miedler et al., 2015). Dolphins resting at the surface had an average stroke volume of approximately 0.8 mL/kg (136 ± 19 mL) and average cardiac output of 32.2 mL/min/kg (with an average heart rate of 41 bpm). As seen in humans and other species after exercise, heart rate, stroke volume, and, therefore, cardiac output, increased significantly in the surfaced dolphins for up to 4 min following cessation of exercise activity (approximately 104%, 63%, 234%, respectively). However, no studies to date have measured stroke volume in diving dolphins. Therefore, whether exercise modulates either stroke volume or cardiac output in diving dolphins is unknown. The cardiovascular flexibility noted in dolphins at rest or after exercise may be a critical evolutionary feature to conserve oxygen during diving by regulating pulmonary and systemic perfusion. For example, cardiovascular adjustments likely minimize blood flow to peripheral musculature during dives, while rapidly removing carbon dioxide and replenishing oxygen during the surface interval. Upon ascent, bradycardia is gradually reversed, suggesting that cardiac output and stroke volume increase (Miedler et al., 2015). Thus, a key event during the dive itself is activation of the sympathetic nervous system to elicit peripheral vasoconstriction. Peripheral vasoconstriction ensures that blood flow is shunted away from peripheral tissues and focused on critical central compartments – the brain and heart. Reversal of this vasoconstriction is essential to replenish oxygen and remove carbon dioxide from those peripheral tissues during the surface interval. Blawas and colleagues demonstrated upregulation of the arachidonate 5-lipoxygenase (ALOX5) gene in dolphins. Since downstream leukotriene metabolites induce vasoconstriction in hypoxic rodent models and humans (Friedman et al., 1984; Ichinose et al., 2001), similar mechanisms may allow marine mammals to tolerate prolonged periods under water (Blawas, Ware, et al., 2021). Peripheral vasoconstriction while diving increases systemic and target organ vascular resistance, and therefore, perfusion states. Vascular resistance, along with blood flow or cardiac output, determine the blood pressure which is frequently monitored
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