Pain Flashcards
Define pain.
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual and potential tissue damage.
Define nociception.
The neural process of encoding noxious stimuli.
Define nociceptive pain.
Pain that arises from actual or threatened damage to non-neural tissue and is due to the activation of nociceptors.
Define neuropathic pain.
Pain caused by a lesion or disease of the somatosensory nervous system.
Define hyperalgesia and give an example.
Increased pain from a stimulus that normally provokes pain.
E.g. palpation normally vs. when bruised
Define allodynia and give an example.
Pain due to stimulus that does not normally provoke pain.
E.g. no longer being able to tolerate being stroked.
What is the difference between acute and chronic pain?
Acute pain lasts a short period of time (minutes/hours to weeks)
Chronic pain lasts longer than a few weeks
What is the biological function of acute pain?
Protective up to a point - e.g. stop an animal walking on a broken leg.
What is the importance of quantification of pain?
Allows categorisation of pain / assessment of treatment efficacy / judgement-making about quality of life.
What are the physiological signs associated with pain?
Increased HR, BP and temp.
Altered respiration
Stress hormones
EEG activity
What signs of pain do both cats and dogs exhibit?
Hunched appearance Pain face Lack of grooming Inappetence Condition-specific signs
What signs of pain do cats exhibit?
Absence of normal behaviour repertoire Hide away at back of cage Unwilling to relax Fear-aggression Resent human contact
What signs of pain do dogs exhibit?
Positive behavioural signs rather than reduced repertoire
More likely to seek attention
Submissive
May be more likely to vocalise
What pain signs might a rabbit exhibit?
Immobility Depression Not grooming Eyes half-closed/shut Bruxism Abnormal body position Change in temperament
What pain signs might a horse exhibit?
Low head carriage Vocalisation Agitation Tail swishing Lameness/limb lifting Pain face Bruxism Muscle fasciculations
List the 7 signs that indicate chronic pain in all species.
Changes in normal behaviour Unkempt coat Loss of body condition/weight loss Slowing down/sleeping more OR more fidgety/restless Signs associated with reluctance to move Difficulty in accessing higher places
What four ways can you score acute pain?
Numerical rating scale
Visual analogue scale
Simple descriptive scale
Dynamic interactive visual analogue scale
What is the issue associated with acute pain score scales?
Inter-observer variation.
Explain the canine composite pain score.
Score out of 20 (dog can’t stand) or 24 (if dog can stand)
Intervention level is 5/20 or 6/24
Explain the feline composite pain score.
Maximum score is 20
Intervention level is 5/20
How do we score chronic pain and why?
Health-related quality of life scoring - shows pattern of pain and wider effects, brings in additional items such as appetite/sleep, includes pain over a period of time (e.g. 7 days).
Why is assessment of health-related quality of life important?
Aids decision-making about analgesia and euthanasia
Improved patient wellbeing through holistic care
Improves continuity of treatment
Helps build and maintain vet-owner relationships
Describe preventative analgesia.
Admin before, during and after procedure
Causes a reduction in intensity/duration of acute pain, and a reduction in chronic pain
Describe multimodal analgesia.
Use of different classes of analgesic agents
Leads to more effective analgesia with lower doses of agents
What is the key pharmacology of opioids in cats/dogs/horses?
Delta/kappa/mu receptor agonists
Full / partial agonists, mixed agonist-antagonists, antagonists
What opioids are used in cats, dogs, horses and rabbits?
Fentanyl Methadone Pethidine (Morphine) Buprenorphine Butorphanol
What are the side effects of opioid use?
Respiratory depression Sedation (dogs) Excitation Bradycardia Nausea/vomiting Decreased GI motility Various effects on urinary system
What is the key pharmacology of NSAIDs?
Inhibit prostaglandin production either through inhibition of COX or LOX.
What are the side effects of NSAID use?
GI ulceration
Renal ischaemia
Hepatopathy
CNS dullness
What is the key pharmacology of local anaesthetics?
Enter nerve fibre, block Na channel, blocks nerve conduction
“Membrane stabilising effect”
Less effective in inflamed tissue due to change in pH
What are the two types of local anaesthetics and give examples?
Ester (no ‘i’ before ‘caine’) - e.g. procaine
Amide (‘i’ before ‘caine’) - e.g. lidocaine/bupivacaine
What are the side effects of local anaesthetic use?
CNS toxicity (occurs at lower doses than CVS) CVS toxicity Do not exceed total safe dose
When/how are local anaesthetics used?
Provide anaesthesia in standing, conscious patient
Postop pain relief
Desensitisation for procedures
Lameness investigation in horses
How can paracetamol be used in animal patients?
Dogs - when NSAIDs are contraindicated
Horses - adjunctive analgesic in painful cases (laminitis)/when NSAIDs are contraindicated
TOXIC to cats!!
State some key facts about gabapentin.
May have a role in management of neuropathic type pain conditions
Sedation is major side effect
Reduce dose over 1-2 weeks (not abruptly) before stopping therapy
State some key facts about amantadine.
Not an analgesic but a hyperalgesic
Excreted via the kidneys
May be helpful in chronic pain states to reverse/obtund central sensitisation
Best used as an adjunctive agent
May take 3-4 weeks to see clinical benefit of therapy
What 2 other drugs may rise in popularity for treatment of chronic pain?
Pregabalin
Amitriptyline
Define epidural.
Epidural = anaesthetics injected into epidural space (via a catheter)
Define spinal.
Spinal = anaesthetic is injected directly into cerebrospinal fluid (via a much smaller needle)
What affects potency of local anaesthetics (LAs) and how does this affect toxicity?
pKa and lipid solubility affect potency
LA toxicity increases as potency increases
What factors affect duration of action of LAs?
Lipid solubility (ease of penetration and amount of drug reaching Na channel)
Strength of binding to channel
Speed of removal
Metabolism of LA
How are the two different types of LAs metabolised?
Esters = hydrolysis by plasma esterases / PABA formed (can cause allergic reactions)
Amides = hydrolysis by cytochrome P450 enzymes in liver
Define baricity and name the molecule usually added to overcome this.
Baricity = weight of one substance compared with weight of equal volume of another (for spinal anaesthesia it is CSF)
Glucose is added to the LA solutions to make them heavier
Explain the addition of vasoconstrictors to LA solutions.
Adrenaline added to reduce speed of systemic absorption/prolong duration of action
Reduces risk of toxicity
Reduces bleed ing at injection site
Describe the CNS toxicity of LAs.
Minor behavioural changes
Muscle twitching and tremors
Tonic-clonic convulsions
CNS/respiratory depression and death
Describe the CVS toxicity of LAs.
Hypotension Dysrhythmias (drug remains bound to Na channels during diastole)
How can we prevent toxicity of LAs?
Do not exceed safe maximum dose
If greater volume needed dilute with NaCl 0.9%
Use appropriately sized syringes/needles
Aspirate before injection to confirm not in blood vessel
