Effects of alfaxalone administered intravenously to healthy yearling loggerhead sea turtles (Caretta caretta) at three different doses

• Autores: Brianne E. Phillips, Lysa P. Posner, Gregory A. Lewbart, Emily F. Christiansen, Craig A. Harms
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 250, Nº. 8, 2017, págs. 909-917
• Idioma: inglés
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• Resumen

  • OBJECTIVE To compare physiologic and anesthetic effects of alfaxalone administered IV to yearling loggerhead sea turtles (Caretta caretta) at 3 different doses.

    DESIGN Randomized crossover study.

    ANIMALS 9 healthy yearling loggerhead sea turtles.

    PROCEDURES Animals received each of 3 doses of alfaxalone (3 mg/kg [1.4 mg/lb], 5 mg/kg [2.3 mg/lb], or 10 mg/kg [4.5 mg/lb]) administered IV in randomly assigned order, with a minimum 7-day washout period between doses. Endotracheal intubation was attempted following anesthetic induction, and heart rate, sedation depth, cloacal temperature, and respirations were monitored. Times to first effect, induction, first voluntary muscle movement, first respiration, and recovery were recorded. Venous blood gas analysis was performed at 0 and 30 minutes. Assisted ventilation was performed if apnea persisted 30 minutes following induction.

    RESULTS Median anesthetic induction time for all 3 doses was 2 minutes. Endotracheal intubation was accomplished in all turtles following induction. Heart rate significantly increased after the 3- and 5-mg/kg doses were administered. Median intervals from alfaxalone administration to first spontaneous respiration were 16, 22, and 54 minutes for the 3-, 5-, and 10-mg/kg doses, respectively, and median intervals to recovery were 28, 46, and 90 minutes, respectively. Assisted ventilation was required for 1 turtle after receiving the 5-mg/kg dose and for 5 turtles after receiving the 10-mg/kg dose. The 10-mg/kg dose resulted in respiratory acidosis and marked hypoxemia at 30 minutes.

    CONCLUSIONS AND CLINICAL RELEVANCE IV alfaxalone administration to loggerhead sea turtles resulted in a rapid anesthetic induction and dose-dependent duration of sedation. Assisted ventilation is recommended if the 10 mg/kg dose is administered.

    Alfaxalone (3-α-hydroxy-5-α-pregnane-11, 20-dione) is a neurosteroid anesthetic agent recently reintroduced into veterinary medicine in the United States.1 The previously marketed formulation contained alphadolone solubilized in a 20% polyoxyethylated castor oil–based surfactant. This formulation was removed from the market after it was associated with histamine release and severe edema in cats and death in dogs.1 The currently marketed formulation contains a different solubilizing compound (cyclodextrin) that does not promote histamine release.

    A GABAA receptor agonist, alfaxalone inhibits action potential propagation and consciousness pathways.1 This drug produces smooth anesthetic inductions when administered to dogs, with dose-dependent cardiovascular depression in both dogs and cats.2,3 Alfaxalone is effective by both IV and IM routes of administration, but the currently marketed formulation is approved only for IV use in dogs and cats in the United States. It also supports less microbial growth than propofol.4 Alfaxalone has been evaluated in reptiles as an anesthetic agent and used clinically as an anesthetic induction agent.5,6 Dose-dependent sedation was observed in green iguanas (Iguana iguana) and Horsfield tortoises (Agrionemys horsfieldii) following IM administration.7,8 In red-eared sliders (Trachemys scripta elegans), IM alfaxalone administration resulted in rapid anesthetic induction, increased loss of muscle tone at increased doses, and longer interval from administration to anesthetic recovery when given at lower temperatures.9,10 In juvenile estuarine crocodiles (Crocodylus porosus) and Australian freshwater crocodiles (Crocodylus johnstoni), IV alfaxalone administration at 4 temperatures resulted in variable duration of sedation, hypersensitivity to stimulation during anesthetic recovery, and apnea 1 to 2 hours following recovery.11 Both injectable and inhalation anesthetics have been evaluated in sea turtle species to allow the development of safe and effective protocols. These include isoflurane, sevoflurane, and combinations of ketamine, midazolam, and either dexmedetomidine or medetomidine.12–16 Although these protocols represent considerable improvements over previously used methods,13 undesirable anesthetic effects, including prolonged recoveries,12 bradycardia,12,13 and apnea,17 remain possible.

    The objective of the study reported here was to evaluate the effects of 3 different doses of alfaxalone administered IV to loggerhead sea turtles (Caretta caretta). It was hypothesized that alfaxalone administration would provide smooth induction and recovery from anesthesia and that anesthetic effects (total sedation score, heart and respiratory rate, and recovery time) would be dose dependent in these turtles.