This document provides information on anesthesia techniques for rats. It discusses the challenges of anesthetizing rats due to their small size and susceptibility to hypothermia. Various pre-anesthetic agents and injectable or inhalant anesthetics are described. Injectable options include combinations of fentanyl/fluanisone, fentanyl/medetomidine, or ketamine/xylazine. Endotracheal intubation techniques are also covered. Proper monitoring, maintenance of temperature, and careful recovery are emphasized to minimize stress on the animals.

1. Anesthesia of the Rat By Katie Krimetz WesternU, DVM 2010 For City of Hope, ARC

2. Introduction Anesthesia use in lab animals Humane restraint Eliminate pain Animal Welfare Implications Minimal stress Analgesia Uneventful recovery Balance with PI work/study requirements Image: Google images

3. Anesthesia Reduces or eliminates pain and anxiety Sedation/tranquilization Mild depression (animal  awake, calm) Analgesia Temporal reduction of pain sensation Anesthesia Temporal and reversible reduction or elimination of sensory and motor responses Local versus Systemic

4. Anesthesia Synergistic effects of compounds possible Allows dose reduction Decreases risk of toxic reactions Minimizes unwanted side-effects Anesthestic depth Monitoring (breathing!) Sensory tests Palpebral reflex Deep pain sensation Hypothermia Image: Google images

5. Rat Anesthesia Innate Difficulties High ratio of surface area to body weight Predisposed to hypothermia IV drug administration limited Small size of superficial veins Small, relatively inaccessable larynx Difficult to intubate Small volumes of anesthesia required Dilutions Occurence of subclinical lung disease Respiratory failure during/after anesthesia

6. (Thurmon, 1999)

7. Rat Anesthesia Pre-Anesthetic Work Antibiotics? YES – if there is a risk of post-op infection Highly resistant to post-op infection (one bolus??) Pre-anesthetic agents Lessen severity of side effects Promotes anesthetic response Sedatives MUST be given if ET tube will be used

8. Pre-Anesthetic Agents IP better than IM Less pain Reduces stress during induction Eases handling and restraint Reduces amounts of other anesthetic agents Can reduce by at least 30-50% Image: Google images

9. Pre-Anesthetic Agents Anticholinergics (atropine) Protects against anesthesia-driven bradycardia Suppresses excessive salivation/bronchial secretion Sedatives Calms the animal Reduces catecholamine release Reduces anesthetic dose needed to promote anesthesia Sedative and muscle relaxant

10. Sedatives Fentanyl/Fluanisone Low dose: sedation, some analgesia High dose: sedation and analgesia (skin biopsy) Can see respiratory depression Reverse if cyanotic (nalbuphine, butorphanol, naloxone) Medetomidine Low dose: light to heavy sedation High dose: lose righting reflex Some strains will require higher doses Little to no analgesia Potentiates other drugs Can reduce amount needed by 60%

11. Sedatives Xylazine Light to moderate sedation Little to no analgesia Potentiates other drugs Ketamine Deep sedation no analgesia Poor muscle relaxation Acepromazine Light sedation, no analgesia Diazepam or Midazolam Light sedation, no analgesia Image: Google images

12. (Flecknell, 2003)

13. Analgesia Provides pain relief Best when administered before surgery Opiates – most effective Buprenorphine, butorphanol, morphine Stimulate opioid receptors in CNS Can stimulate or depress CNS, depending on dose Depression: analgesia, respiratory depression, sedation Stimulation: excitement Peripherally acting Antihistamines, local anesthetics NSAIDs Aspirin, acetaminophen

14. Anesthesia - Injectables Slow onset of drug effects Difficulty in controlling anesthetic level High metabolic rates Require large doses, compared to larger animals Always consider: Route, volume, discomfort Dilution can reduce discomfort Absorption rates vary IM and IP used with drugs with wide safety margin Cannot “give to effect” Gender differences Female rats are more sensitive to pentobarbital

15. Anesthesia - Injectables Fentanyl/Fluanisone or Fentanyl/Droperidol Combination with diazepam/midazolam Superior anesthesia and muscle relaxation in rats Lengthens duration of anesthesia (20-40 min) Additional doses can allow longer periods of anesthesia Reverse with nalbuphine or butorphanol Fentanyl and Medetomidine 60 minute surgery anesthesia Rapid recovery Reversed with nalbuphine or butorphanol and atipamezole Induction and recovery can be improved by acclimatization

16. Anesthesia - Injectables Ketamine and Xylazine 30 minutes of surgical anesthesia Dissociative anesthetic  not for rats? Instead of xylazine  medetomidine (specific alpha-2-agonist) Less side effects, easier to reverse Pentobarbital – widely used Short-acting Narrow dose-response range, respiratory depression Hypothermia Thiopental (Pentohal) Short-acting, Alkaline nature (IV only) Alpha-chloralose Used only in non-survival procedures, no analgesia Good choice for physiological experiments

17. Assuming no pre-op meds were given… (Flecknell, 2003)

18. Assuming no pre-op meds were given… (Flecknell, 2003)

19. (Flecknell, 2003)

20. Endotracheal Intubation Measure tube length Intubate one bronchus Tape/tie tube in place Tongue pulled forward and to side Purpose-made otoscope Introducer/guide wire passed through larynx Direct vision! Remove otoscope Thread 16-12g catheter over guide wire Image: Google images Image: Google images

21. Image: Google images

22. Image: Google images Image: Google images Image: Flecknell, 2003 Image: Google images

23. Image: Paddleford, 1999

24. Image: Flecknell, 2003

25. Endotracheal Intubation Neck can be transilluminated Open mouth with gag Pull tongue forward See bright flashing light Opening and closing of larynx Image: Google images

26. Inhalation Anesthesia Precise anesthetic control Minimum Alveolar Concentration (MAC) Alveolar concentration of compound at 1atm that will prevent a response to painful stimuli in 50% of animals Lower MAC = high potency 1.2 – 1.3 MAC suitable for sx Anesthetic Chamber Minimal control, short term ET tube for maintenance Image: Google images

27. Inhalation Anesthesia Agents: Halothane 2-3% induction, 0.5% maintenance Recovery in 10-20 min Can cause resp depression, hypotension, and vent. Fibrillation Isoflurane Respiratory depression Less cardiovascular problems than with halothane Sevoflurane Others: enflurane, methoxyflurane, diethyl ether, NO Don’t forget mechanical ventilation!

28. Inhalation Anesthesia Management Prevent hypothermia Heating pad/lamp Insulating material Recovery Excitement phase is greatest risk Recovery should be in a cage External temperature should be controlled Anesthesia can cause hypothermia Rats: ideally keep in 35°C Image: Google images

29. References Paddleford, Robert R. Manual of Small Animal Anesthesia, 2nd Edition. W.B. Saunders Company, 1999. Flecknell, P. Laboratory Animal Anesthesia, 2nd Edition. Elsevier, 2003. Thurmon, John C.; Tranquilli, William J.; Benson, G. John. Essentials of Small Animal Anesthesia & Analgesia. Lippincott Williams & Wilkins, 1999. Red Rat Book

30. Questions ?