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Rat Anesthesia
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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

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

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    Rat Anesthesia Rat Anesthesia Presentation Transcript

    • Anesthesia of the Rat
      By
      Katie Krimetz
      WesternU, DVM 2010
      For
      City of Hope, ARC
    • 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
    • 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
    • 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
    • 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
    • (Thurmon, 1999)
    • 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
    • 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
    • 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
    • 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%
    • 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
    • (Flecknell, 2003)
    • 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
    • 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
    • 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
    • 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
    • Assuming no pre-op meds were given…
      (Flecknell, 2003)
    • Assuming no pre-op meds were given…
      (Flecknell, 2003)
    • (Flecknell, 2003)
    • 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
    • Image: Google images
    • Image: Google images
      Image: Google images
      Image: Flecknell, 2003
      Image: Google images
    • Image: Paddleford, 1999
    • Image: Flecknell, 2003
    • 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
    • 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
    • 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!
    • 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
    • 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
    • Questions ?