Sources of variability in the duration of anesthesia in snakes dan preston
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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

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Sources of variability in the duration of anesthesia in snakes dan preston l.jpg
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 l.jpg
Why Anesthetize Reptiles? Snakes

  • 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 l.jpg
Challenges Associated with Snakes Reptile Anesthesia

  • Risk of Mortality

  • Unique Physiology and Anatomy

  • Difficult Drug Administration

  • Variability in Anesthetic Effect

www.snakegetters.com


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Anesthetic Agents used Snakes on Reptiles

  • Cold Narcosis, Inhalants and Injectables


Brevital sodium l.jpg
Brevital Sodium Snakes

  • 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 l.jpg
Questions Snakes

  • What factors are responsible for variability between individuals?

  • How can anesthetic protocols be improved to create more consistent results?


Red sided garter snakes thamnophis sirtalis parietalis l.jpg
Red-sided Garter Snakes Snakes (Thamnophis sirtalis parietalis)

  • Well-studied

  • Large sample sizes

  • Easily maintained

    in captivity


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Potential Causes of Variability in Duration of Anesthesia Snakes

  • 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 l.jpg
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 cont10 l.jpg
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 l.jpg
Methods: Anesthetic Protocol cont.

  • 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 l.jpg
Methods: Experimental Designs cont.

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

-60-70 cm SVL, 60-120 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 l.jpg
Results: Body Temperature cont.

One way ANOVA:

F2,17 = 12.71

P < 0.001

Post-hoc Tukey:

21 vs 31, P < 0.001

21 vs 26, P = 0.037

26 vs 31, P = 0.042


Results body condition l.jpg
Results: Body Condition cont.

One way ANOVA:

F2,42 = 5.026

P = 0.011

Post-hoc Tukey:

Thin vs Fat, P = 0.008

Thin vs Med., P = 0.300

Med. vs Fat, P = 0.230


Results time post feeding l.jpg
Results: Time Post-feeding cont.

One way repeated measures ANOVA:

F2,17 = 3.091

P =0.057


Conclusions l.jpg
Conclusions cont.

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


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Acknowledgements cont.

Thanks to:

Dr. Robert Mason

Dr. Craig Mosley

Dr. Kevin Ahern

Rocky Parker

Chris Friesen

Howard Hughes Medical Institute


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Pharmacokinetics of Barbiturates cont.

Thurmon, Tranquili and Benson. 1999. Essentials of Small Animal Anesthesia and Analgesia.


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