Rat Anesthesia

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Nov 2008 - A presentation given during my lab animal rotation; reivews procedures, risks, and techniques for anesthetizing rats, focused on use in lab animal medicine

Rat Anesthesia

  1. 1. Anesthesia of the Rat<br />By<br />Katie Krimetz<br />WesternU, DVM 2010<br />For<br />City of Hope, ARC<br />
  2. 2. Introduction<br />Anesthesia use in lab animals<br />Humane restraint<br />Eliminate pain<br />Animal Welfare Implications<br />Minimal stress<br />Analgesia<br />Uneventful recovery<br />Balance with PI work/study requirements<br />Image: Google images<br />
  3. 3. Anesthesia<br />Reduces or eliminates pain and anxiety<br />Sedation/tranquilization<br />Mild depression (animal  awake, calm)<br />Analgesia<br />Temporal reduction of pain sensation<br />Anesthesia<br />Temporal and reversible reduction or elimination of sensory and motor responses<br />Local versus Systemic<br />
  4. 4. Anesthesia<br />Synergistic effects of compounds possible<br />Allows dose reduction<br />Decreases risk of toxic reactions<br />Minimizes unwanted side-effects<br />Anesthestic depth<br />Monitoring (breathing!)<br />Sensory tests<br />Palpebral reflex<br />Deep pain sensation<br />Hypothermia<br />Image: Google images<br />
  5. 5. Rat Anesthesia<br />Innate Difficulties<br />High ratio of surface area to body weight<br />Predisposed to hypothermia<br />IV drug administration limited<br />Small size of superficial veins<br />Small, relatively inaccessable larynx<br />Difficult to intubate<br />Small volumes of anesthesia required<br />Dilutions<br />Occurence of subclinical lung disease<br />Respiratory failure during/after anesthesia<br />
  6. 6. (Thurmon, 1999)<br />
  7. 7. Rat Anesthesia<br />Pre-Anesthetic Work<br />Antibiotics?<br />YES – if there is a risk of post-op infection<br />Highly resistant to post-op infection (one bolus??)<br />Pre-anesthetic agents<br />Lessen severity of side effects<br />Promotes anesthetic response<br />Sedatives MUST be given if ET tube will be used<br />
  8. 8. Pre-Anesthetic Agents<br />IP better than IM<br />Less pain<br />Reduces stress during induction<br />Eases handling and restraint<br />Reduces amounts of other anesthetic agents<br />Can reduce by at least 30-50%<br />Image: Google images<br />
  9. 9. Pre-Anesthetic Agents<br />Anticholinergics (atropine)<br />Protects against anesthesia-driven bradycardia<br />Suppresses excessive salivation/bronchial secretion<br />Sedatives<br />Calms the animal<br />Reduces catecholamine release<br />Reduces anesthetic dose needed to promote anesthesia<br />Sedative and muscle relaxant<br />
  10. 10. Sedatives<br />Fentanyl/Fluanisone<br />Low dose: sedation, some analgesia<br />High dose: sedation and analgesia (skin biopsy)<br />Can see respiratory depression<br />Reverse if cyanotic (nalbuphine, butorphanol, naloxone)<br />Medetomidine<br />Low dose: light to heavy sedation<br />High dose: lose righting reflex<br />Some strains will require higher doses<br />Little to no analgesia<br />Potentiates other drugs<br />Can reduce amount needed by 60%<br />
  11. 11. Sedatives<br />Xylazine<br />Light to moderate sedation<br />Little to no analgesia<br />Potentiates other drugs<br />Ketamine<br />Deep sedation<br />no analgesia<br />Poor muscle relaxation<br />Acepromazine<br />Light sedation, no analgesia<br />Diazepam or Midazolam<br />Light sedation, no analgesia<br />Image: Google images<br />
  12. 12. (Flecknell, 2003)<br />
  13. 13. Analgesia<br />Provides pain relief<br />Best when administered before surgery<br />Opiates – most effective<br />Buprenorphine, butorphanol, morphine<br />Stimulate opioid receptors in CNS<br />Can stimulate or depress CNS, depending on dose<br />Depression: analgesia, respiratory depression, sedation<br />Stimulation: excitement<br />Peripherally acting<br />Antihistamines, local anesthetics<br />NSAIDs<br />Aspirin, acetaminophen<br />
  14. 14. Anesthesia - Injectables<br />Slow onset of drug effects<br />Difficulty in controlling anesthetic level<br />High metabolic rates<br />Require large doses, compared to larger animals<br />Always consider: Route, volume, discomfort<br />Dilution can reduce discomfort<br />Absorption rates vary<br />IM and IP used with drugs with wide safety margin<br />Cannot “give to effect”<br />Gender differences<br />Female rats are more sensitive to pentobarbital<br />
  15. 15. Anesthesia - Injectables<br />Fentanyl/Fluanisone or Fentanyl/Droperidol<br />Combination with diazepam/midazolam<br />Superior anesthesia and muscle relaxation in rats<br />Lengthens duration of anesthesia (20-40 min)<br />Additional doses can allow longer periods of anesthesia<br />Reverse with nalbuphine or butorphanol<br />Fentanyl and Medetomidine<br />60 minute surgery anesthesia<br />Rapid recovery<br />Reversed with nalbuphine or butorphanol and atipamezole<br />Induction and recovery can be improved by acclimatization<br />
  16. 16. Anesthesia - Injectables<br />Ketamine and Xylazine<br />30 minutes of surgical anesthesia<br />Dissociative anesthetic  not for rats?<br />Instead of xylazine  medetomidine (specific alpha-2-agonist)<br />Less side effects, easier to reverse<br />Pentobarbital – widely used<br />Short-acting<br />Narrow dose-response range, respiratory depression<br />Hypothermia<br />Thiopental (Pentohal)<br />Short-acting, Alkaline nature (IV only)<br />Alpha-chloralose<br />Used only in non-survival procedures, no analgesia<br />Good choice for physiological experiments<br />
  17. 17. Assuming no pre-op meds were given…<br />(Flecknell, 2003)<br />
  18. 18. Assuming no pre-op meds were given…<br />(Flecknell, 2003)<br />
  19. 19. (Flecknell, 2003)<br />
  20. 20. Endotracheal Intubation<br />Measure tube length<br />Intubate one bronchus<br />Tape/tie tube in place<br />Tongue pulled forward and to side<br />Purpose-made otoscope<br />Introducer/guide wire passed through larynx<br />Direct vision!<br />Remove otoscope<br />Thread 16-12g catheter over guide wire<br />Image: Google images<br />Image: Google images<br />
  21. 21. Image: Google images<br />
  22. 22. Image: Google images<br />Image: Google images<br />Image: Flecknell, 2003<br />Image: Google images<br />
  23. 23. Image: Paddleford, 1999<br />
  24. 24. Image: Flecknell, 2003<br />
  25. 25. Endotracheal Intubation<br />Neck can be transilluminated<br />Open mouth with gag<br />Pull tongue forward<br />See bright flashing light<br />Opening and closing of larynx<br />Image: Google images<br />
  26. 26. Inhalation Anesthesia<br />Precise anesthetic control<br />Minimum Alveolar Concentration (MAC)<br />Alveolar concentration of compound at 1atm that will prevent a response to painful stimuli in 50% of animals<br />Lower MAC = high potency<br />1.2 – 1.3 MAC suitable for sx<br />Anesthetic Chamber<br />Minimal control, short term<br />ET tube for maintenance<br />Image: Google images<br />
  27. 27. Inhalation Anesthesia<br />Agents:<br />Halothane<br />2-3% induction, 0.5% maintenance<br />Recovery in 10-20 min<br />Can cause resp depression, hypotension, and vent. Fibrillation<br />Isoflurane<br />Respiratory depression<br />Less cardiovascular problems than with halothane<br />Sevoflurane<br />Others: enflurane, methoxyflurane, diethyl ether, NO<br />Don’t forget mechanical ventilation!<br />
  28. 28. Inhalation Anesthesia<br />Management<br />Prevent hypothermia<br />Heating pad/lamp<br />Insulating material<br />Recovery<br />Excitement phase is greatest risk<br />Recovery should be in a cage<br />External temperature should be controlled<br />Anesthesia can cause hypothermia<br />Rats: ideally keep in 35°C<br />Image: Google images<br />
  29. 29. References<br />Paddleford, Robert R. Manual of Small Animal Anesthesia, 2nd Edition. W.B. Saunders Company, 1999.<br />Flecknell, P. Laboratory Animal Anesthesia, 2nd Edition. Elsevier, 2003.<br />Thurmon, John C.; Tranquilli, William J.; Benson, G. John. Essentials of Small Animal Anesthesia & Analgesia. Lippincott Williams & Wilkins, 1999.<br />Red Rat Book<br />
  30. 30. Questions ?<br />

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