Comparing Tricaine Methanesulfonate (MS-222) and Propofol's Influence on Acid-Base Status in Leopard Sharks (Triakis semifasciata) during Anesthesia
Western University of Health Sciences, College of Veterinary Medicine, Pomona, CA, USA
Abstract
Tricaine methanesulfonate (MS-222) is used to anesthetize elasmobranchs for exams and surgical procedures. Recently propofol has been identified as an alternative anesthetic for use in elasmobranches.1 A thorough comparison of MS-222 and propofol's influence on blood gas values in elasmobranches has yet to be conducted. The aim of this study was to compare blood pH, partial pressure O2 (pO2) partial pressure CO2 (pCO2), saturated O2 (sO2), bicarbonate (HCO3-), and lactate in leopard sharks (Trikas semifasciata) anesthetized with MS-222 and propofol respectively. It is thought lactate levels may be predictive for short-term postoperative survival rate in fish.2 Because MS-222 is a well known respiratory depressant it was hypothesized that MS-222 would significantly depress each animal's acid-base status making the animals more acidotic post operatively compared to propofol, which does not significantly depress respiration or heart rate in elasmobranchs.1,2,3 Prior to experimental trials, five leopard sharkswere surgically catheterized via the caudal tail vein in order to obtain serial blood samples. Two anesthetic treatment groups were established: propofol (2.5 mg/kg), and MS-222 (150 mg/L induction, 75 mg/L maintenance) with sharks serving as their self controls. The sharks were initially anesthetized in enclosure water (18°C, 8.2 pH) using propofol. After a 24hr-withdrawl period, the same animals were anesthetized using MS-222 (19°C water with an adjusted pH of 8.3). During the experimental trials animals were maintained in a piscine re-breathing apparatus. In each treatment blood was drawn prior to anesthesia using tonic immobility and repeated every 15 minutes while anesthetized for a total duration of 60 minutes. Blood samples were analyzed using iStat Portable Clinical analyzer (Heska Corp.) immediately upon collection. Throughout anesthesia anesthetic plane was evaluated every 15 minutes using respiratory rate, righting reflex, escape response, and response to noxious stimuli. Data was analyzed by repeated measures ANOVA. Between the two anesthetic treatments, a statistically significant difference in blood pH (p = 0.0046) and pCO2 (p = 0.0331) was found. HCO3- and lactate values statistically differed in relation to time of sampling with each animal (p ≤ 0.0001 for both measures), but did not differ between treatment groups. PO2 and sO2 had no statistical difference between treatment groups or sampling times. This data provides empirical evidence for acid-base status in elasmobranchs undergoing prolonged procedures using two different anesthetic protocols. Propofol as an anesthetic for elasmobranchs allows for a tighter control of blood pH and pCO2 during anesthesia compared to MS-222; however, it is clear lactate levels still elevate over time while elasmobranchs are under both anesthetic. If lactate is a true indicator in a shark's short-term postoperative survival rate, selection of anesthetic protocols is not as large of an influence on a shark's survival compared to time under anesthesia.
Acknowledgements
The authors wish to thank the California Science Center for facilities and animal provisions along with aquarist staff and veterinary technician support, Western University of Health Sciences associate professor Dr. Carlos Crocker for technical support, Dr. Lance Adams of The Aquarium of the Pacific for equipment usage, Dr. Tom Phillips, Western University of Health Sciences - College of Veterinary Medicine for their financial support.
References
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