Analgesia

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Analgesia

• Belinda Farnfield

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Do animals experience pain?

• Pain
• conscious perception of a noxious stimulus
• One argument
• Animals have less developed cortex
• Noxious stimulus present
• Not perceived to same degree
• No/ little analgesia administered

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Evidence that they do perceive pain

• They will self administer analgesics
• Also
• We cannot prove they do not perceive pain
• We justify animal use in pain models to develop
  novel analgesics

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Different approach

• Not When should I administer analgesia?
• Instead Are there any specific reasons why
  analgesics would interfere with the procedure?
• If a painful procedure is carried out with no
  analgesia, must justify
• But - repeated doses doses of analgesics have
  side effects (a cost), with no benefit to the
  animal if it is not experiencing pain

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Careful thought needed

• Be objective
• Administer analgesics based on
• recognition of normal behaviour for the species
  individual
• Recognition of pain behaviours for the species
• palpate the affected area
• make measurements eg bodyweight

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Analgesic drugs

• NSAIDs
• Local analgesics
• Opioids

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NSAIDs

• Carprofen main one used
• Fewer side effects than older NSAIDs
• Give before anaesthesia

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Why give a NSAID before anaesthesia?

• If block pain before it is perceived in the
  central nervous system, evidence that this leads
  to better overall analgesia
• If wait till pain has occurred, more difficult to
  block
• Due to central sensitisation
• Plasticity in spinal cord
• Non-pain pathways begin to transmit pain signals

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Local analgesics

• Topical application
• Infiltrate in wound area using needle and syringe
• Regional nerve blocks
• farm animal species
• Look up the toxic dose for the drug you are using
  in the species you are working with

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Opioids

• Classical opioid
• morphine
• full agonist a the ? receptor
• Partial agonists commonly used
• buprenorphine
• provide analgesia
• less respiratory depression

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Practical use of opioids

• After use of a pure ? agonist (eg fentanyl) as
  part of an anaesthetic regimen
• administer a mixed agonist/ antagonist or
  partial agonist (eg nalbuphine or buprenorphine)
• Less respiratory depression, analgesia maintained
• Reversal with opioid antagonist eg naloxone
  undesirable as no analgesia

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An analgesia regimen

• What is the severity of the pain?
• Likely duration
• Which species?
• What is the nursing care?
• During working day?
• Out of hours
• Which drugs could be used?
• What are the side effects?
• Could the analgesic interfere with procedure eg
  if they act at a receptor that you are studying

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Which drugs to use

• Local analgesia if possible
• NSAID
• Opioid as well for more painful procedures

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Timing of administration

• Before the painful stimulus
• Repeat at intervals
• Must be able to recognise abnormal behaviours in
  the species you are working with

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Behaviours associated with pain in the rat

• Three have been identified in rats following
  abdominal surgery
• Twitching seen when rat is resting
• Involuntary muscle contraction
• Fur moves spasmodically
• Back-arching
• Like a cat when waking
• Falling
• Momentary loss of balance

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Video clips from Pain Assessment in the Rat CD

• Excellent CD available from University of
  Newcastle, shows pain assessment scheme developed
  by John V Roughan and Paul A Flecknell
• Worth buying and working through in your own time
  (current price 5 pounds sterling)
• See www.lal.org.uk/digital.htm
• Video clip Rat pain behaviours (5 minutes)

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Lack of data for other procedures and species

• Collect objective data
• Write it down
• Review at the end of each experiment