Optimal Protocol for Intravenous Introduction to Inhalant Anaesthesia in Chelonians
Avian and Exotic Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Brno, Czech Republic
Professor Zdenek Knotek (Sid) graduated from Veterinary University Brno in 1982 (with honours). Head of the Avian and Exotic Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic. Sid is a founding member and diplomate of the European College of Zoological Medicine, member of ARAV, past-president of EAZWV, president of CAZWV. Sid had teaching activities in Budapest, Copenhagen, Kosice, Ljubljana, Utrecht, Vienna, Warsaw, Purdue (USA), Denpasar (Indonesia). As a founder of reptile medicine specialty he headed the Unit for Birds and Reptiles at Vetmeduni Vienna (2010–2013). Sid supervises courses: Summer School for Exotic Medicine and Surgery (since 2004) and ESAVS courses - Exotic Pets Medicine and Surgery I, II, III (since 2005). His current focus involves medicine and surgery in reptiles, small mammals and birds.
In chelonians, the optimal protocol for smooth induction of anaesthesia and uneventful recovery is needed. Inhalation anaesthesia is a very safe and effective method of anaesthesia in chelonians, but it is also difficult due to very strong head and neck withdrawal reflex and the ability of terrapins and tortoises to hold their breath for extended time. Induction with an injectable agent which allows safe tracheal tube insertion to inhalation anaesthesia is therefore required.
Dissociative anaesthetics (ketamine, tiletamine) in combination with α-2 agonists (xylazine, medetomidine, dexmedetomidine) administered intramuscularly, and propofol or alfaxalone (3-α-hydroxy-5-α-pregnane-11,20-dione) administered intravenously have been reported as being used for effective sedation or anaesthesia in reptiles.1-3 Alfaxalone has been tested in reptiles also by intramuscular route4, where high dosages were required to obtain anaesthetic effects. In published studies conducted on the intravenous administration of alfaxalone in reptiles there is a variation in recommended dose rates and degree of anaesthetic monitoring. The aim of this presentation is to inform practicing veterinarians about the protocol of easy introduction to inhalant anaesthesia with low dose of short-acting anaesthetic agent alfaxalone in terrapins and tortoises.
This study involved 77 chelonians: 33 red-eared terrapins (Trachemys scripta elegans), 11 Hermann´s tortoises (Testudo hermanni), 8 spur-thigh tortoises (Testudo graeca), 10 marginated tortoises (Testudo marginata), 12 Russian tortoises (Testudo horsfieldi), and 3 African spur thigh tortoises (Geochelone sulcata). Chelonians were patients presented to the Avian and Exotic Animal Clinic for different surgical treatments (soft tissue surgery, ovariectomy, salpingotomy, reposition of penile or cloaca prolapse, penile amputation, orthopaedic surgery on the shell and limbs). After fasting for 24 h the patients received a combination of meloxicam (1 mg/kg intramuscularly, Metacam 5 mg/ml, Boehringer Ingelheim, Germany) with butorphanol (2 mg/kg intramuscularly, Torbugesic 10 mg/ ml, Pfizer, Spain), 25–35 minutes before the alfaxalone administration. Alfaxalone (Alfaxan® 10 mg/ml; Vétoquinol, France) was administered as a bolus dose of 5 mg/kg via the subcarapacial (subvertebral) sinus. The patients were placed on an electric heating pad (Bosch PFP 1031; Bosch, Czech Republic) kept at 37.5°C and tracheal tube was inserted for the isoflurane inhalation anaesthesia (5–3% Isofluran, Nicholas Piramal, Piramal Healthcare UK, combined with oxygen 0.6–1.0 l/min; intermittent positive pressure ventilation maintained by small animal ventilator SAV03, Vetronic Services UK ).
Selected clinical indicators were continuously recorded including the loss of the head, neck, and leg withdrawal reflex, loss of glottal control enabling the insertion of the endotracheal tube, loss of toe-pinch reflex on the pelvic limb, restoration of toe-pinch reflex, restoration of the head, neck, and leg withdrawal reflex and voluntary movement. The time from the injection of alfaxalone to the loss of the head, neck, and leg withdrawal reflex was recorded as induction time. The time from the injection of alfaxalone to the loss of glottal control was recorded as tracheal tube insertion time. Chelonians with tracheal tube inserted were ventilated with air by the use of ventilator (intermittent positive pressure ventilation maintained by small animal ventilator SAV03, Vetronic Services UK). The time from the injection of alfaxalone to the loss of the toe-pinch-reflex was recorded as a time to deep pain sensation loss. The time from the loss of the toe-pinch reflex to the restoration of the toe-pinch reflex was recorded as surgical plane of anaesthesia interval. The time from the administration of alfaxalone to the restoration of the head, neck, and leg withdrawal reflex and voluntary movement was recorded as the time of full recovery.5
Intravenous alfaxalone anaesthesia performed well as an induction agent, with rapid onset of activity allowing tracheal tube insertion and a short period of deep pain sensation loss and a more protracted period equating to a surgical plane of anaesthesia, with full recovery (where inhalational agents not used) approximately half an hour post induction. The head, neck, and leg withdrawal reflex was lost within 25 seconds and the time to deep pain sensation loss was 35–40 seconds. The tracheal tube insertion time, the time of surgical plane of anaesthesia, and full recovery time were 40 seconds, 27 minutes and 40 minutes, respectively.
In chelonians, smooth induction of anaesthesia and uneventful recovery has previously shown to be achievable with high doses of alfaxalone administered intramuscularly.4 Our clinical experience showed intravenous use of alfaxalone at a dose of 5 mg/kg to be a suitable method of short term anaesthesia for tracheal tube insertion and induction to inhalation anaesthesia in terrapins and tortoises.6 Our results are in full accordance with other authors that described a reliable induction of anaesthesia in reptiles with the loss of deep pain sensation within the first two minutes after intravenous administration of alfaxalone at the dose rate of 2–4 mg/kg and full restoration of activity 10 to 30 minutes later.1-2 The benefits of alfaxalone administered to reptiles intravenously include rapid induction and fast recovery.7 Our findings in terrapins and tortoises are similar to those reported in lizards,8,9 except that time intervals that were monitored within the anaesthesia are longer in chelonians. These differences may result from unique physiological responses of cardiac and respiratory systems to anaesthetic agents, observed in particular taxonomic groups of reptiles.5
Intravenous use of alfaxalone in dose of 5 mg/kg proved to be a suitable method of induction to inhalation anaesthesia in terrapins and tortoises. The presented protocol did not result in any anaesthetic complications or deaths.
This project received partial support from the Internal Grant Agency of the University of Veterinary and Pharmaceutical Sciences Brno (IGA Nr. 32/2010/FVL). The study was performed together with Eva Cermakova, DVM; Silvia Barazorda Romero, DVM; and Anna Musilova, DVM. The authors extend their thanks to Dr. Robert S.P. Johnson, BVSc, MACVSc, CertZooMed, South Penrith Veterinary Clinic, New South Wales, Australia, for his valuable comments.
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