Sources of Variability in the Duration of Anesthesia in Snakes Dan Preston Mentors: Dr. Robert Mason, Department of Zoology Dr. Craig Mosley, College of Veterinary Medicine Oregon State University

Why Anesthetize Reptiles? Anesthesia facilitates invasive procedures such as surgery Veterinary Medicine –Reptiles are pets Research –Experiments often involve surgical procedures Ihooq38/flickr.com

Challenges Associated with Reptile Anesthesia Risk of Mortality Unique Physiology and Anatomy Difficult Drug Administration Variability in Anesthetic Effect

Anesthetic Agents used on Reptiles Cold Narcosis, Inhalants and Injectables

Brevital Sodium Barbiturate anesthetic Work in the brain at GABA receptors; suppress CNS Widely used in many reptile taxa Intramuscular or subcutaneous administration Fast acting; short induction and recovery times Variable effects across individuals

Questions 1.What factors are responsible for variability between individuals? 2.How can anesthetic protocols be improved to create more consistent results?

Red-sided Garter Snakes (Thamnophis sirtalis parietalis) Well-studied Large sample sizes Easily maintained in captivity

Potential Causes of Variability in Duration of Anesthesia 1.Body temperature -Reptiles are ectotherms; heart rate increases with body temperature -High temperatures increase rates of distribution and metabolism of anesthetics

Potential Causes of Variability in Duration of Anesthesia cont. 2. Body condition -Barbiturates distribute from blood to viscera, lean tissue and then accumulate in adipose tissue over time C.R.Friesen

Potential Causes of Variability in Duration of Anesthesia cont. 3. Time post-feeding - Snakes have evolved to efficiently digest large meals at infrequent intervals - Upregulate heart, gut and liver after feeding - Brevital sodium distributes to the gut and is metabolized hepatically

Methods: Anesthetic Protocol Anesthetize snakes with 15 mg/kg subcutaneously Record loss of righting ability, beginning and end of surgical anesthesia, return of righting ability Measure body temperature every 30 min.

Methods: Experimental Designs 1. Body Temperature -20 males, 3 temps. (21C, 26C, 31C) -repeated measures 2. Body Condition -45 females, 3 body condition groups, all at 21 C cm SVL, g body weight 3. Time Post-feeding -10 males, 10 females, all at 21 C -anesthetized 1, 3, 10 days post-feeding -dosage based on pre-feeding masses

Results: Body Temperature One way ANOVA: F 2,17 = P < Post-hoc Tukey: 21 vs 31, P < vs 26, P = vs 31, P = 0.042

Results: Body Condition One way ANOVA: F 2,42 = P = Post-hoc Tukey: Thin vs Fat, P = Thin vs Med., P = Med. vs Fat, P = 0.230

Results: Time Post-feeding One way repeated measures ANOVA: F 2,17 = P =0.057

Conclusions 1. Body temperature has strong effect –Increased heart rate likely reduces anesthetic duration 2. Body condition has moderate effect –Shortened anesthetic duration with brevital sodium in fatter snakes is probably due to absorption by adipose tissue 3. Time post-feeding did not have a detectable effect –Physiological changes during digestion may not have clinically significant effect on anesthesia –Further studies may clarify whether any effect exists

Acknowledgements Thanks to: Dr. Robert Mason Dr. Craig Mosley Dr. Kevin Ahern Rocky Parker Chris Friesen Howard Hughes Medical Institute

Pharmacokinetics of Barbiturates Thurmon, Tranquili and Benson Essentials of Small Animal Anesthesia and Analgesia.