Abstract
Safe restraint of elasmobranchs for clinical procedures, transport or other activities can be challenging, particularly in larger species. Various anesthetics have been used with mixed success in different elasmobranchs.1-6 Few studies have evaluated larger groups of animals or blood gas and cardiorespiratory parameters in these species.1,6 Propofol is a highly lipid soluble compound that modulates the inhibitory function of the neurotransmitter gamma-aminobutyric acid subtype A (GABAA) in the brain. It has a wide safety margin, is rapidly metabolized with short duration of effect and is non-cumulative. It decreases intracranial pressure and can cause respiratory depression and systemic hypotension. It is non-reversible, does not provide analgesia, and must be given intravenously. A previous study on the clinical and cardiorespiratory effects of propofol in spotted bamboo sharks (Chylloscyllium plagiosum)6 determined that 2.5 mg/kg was well tolerated by these sharks, was sufficient to reach a surgical plane of anesthesia, and did not significantly affect heart or respiratory rate. The current study expands on propofol use in different elasmobranch species and evaluates blood gas parameters in addition to cardiorespiratory effects.
Propofol (Propoflo, Abbott Laboratories, Princeton, NJ, USA) was administered to 13 individual juvenile and adult bonnethead sharks (Sphyrna tiburo) at either 4 mg/kg (n = 6) or 5 mg/kg (n = 7) via the first dorsal sinus. Blood was collected from the ventral tail vein of each animal immediately following onset of anesthesia for CBC, chemistry and blood gas measurements using a point of care analyzer (iSTAT, Abbott Labs, Princeton, NJ). Parameters measured included pH, PCO2 and PO2 (all adjusted for water temperature), base excess, HCO3, TCO2, O2 saturation, and lactate. Additional blood samples were collected 15 and 30 minutes after the initial sample to further monitor changes in blood gas parameters. Most parameters were stable throughout anesthesia though lactate rose steadily in each animal over time. Heart and respiratory rates were measured for each animal throughout anesthesia, and while heart rates were generally stable among both groups, respiratory rates varied greatly among individuals. All recovered well and were swimming normally between 32–65 minutes post-induction.
Based on results from the controlled bonnethead study, six adult sandtiger sharks (Carcharias taurus) were anesthetized with propofol via the first dorsal sinus for physical examination, blood collection, spinal radiographs and transport. Animals were dosed based on weight estimates; actual dosages ranged between 2.7–3.7 mg/kg. All dosages resulted in surgical plane of anesthesia (loss of righting, no response to handling or stimulation) and all displayed severely reduced respirations within 5 minutes post-induction. Blood was collected from the ventral tail vein within 15 minutes post-induction for blood gas analysis, CBC, and a comprehensive chemistry panel. Follow-up blood samples were collected from 4 of the animals 40–60 minutes post-induction. Lactate increased over time for each animal evaluated, though to a lesser degree than that observed in the bonnetheads. Other parameters varied between animals and all recovered fully within 2.5 hours. In summary, propofol is easily administered through the dorsal sinus in bonnethead and sandtiger sharks, and appears to be safe, reliable and effective in these species.
Acknowledgements
We are very grateful to our veterinary technicians Lynda Leppert, Nicole Hatcher, Mayela Alsina and Jeff Ingle for their excellent quality of work, Brittany Stevens for her exceptional assistance, and our staff biologists for their consistently outstanding animal care.
* Presenting author
Literature Cited
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