Pain Lecture Flashcards
Define pain.
Pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. - International Association for the Study of Pain
What are the benefits of treating pain?
Physical -
- improved sleep, better appetite
- fewer medical complications (e.g. MI, pneumonia)
Psychological
- reduced sufferring
- less depression
Societal
- lower health costs e.g. shorter hospital stay
- able to contribute to society
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How can you classify pain?
By duration
- Acute
- Chronic
- Acute on chronic
Cause
- Cancer
- Non cancer
Mechanism
- Nociceptive
- Neuropathic
Distinguish acute and chronic pain.
Acute - pain of recent onset and probable limited duration
Chronic - pain lasting more than 3 months; pain lasting after normal healing; often no identifiable cause
What are the differences between cancer and non-cancer pain?
Cancer pain - progressive. may be mixture of chronic and acute
Non-cancer pain - many different causes, acute or chronic
Non-cancer pain - fracture, appendicitis.
What is nociceptive pain? Describe it.
- •Obvious tissue injury or illness
- •Also called physiological or inflammatory pain
- •Protective function
- •Description
- –Sharp ± dull
- –Well localised
Describe neuropathic pain.
- Nervous system damage or abnormality
- Tissue injury may not be obvious
- Does not have protective function
- Description
- Burning, shooting and/or numbness, pins and needles
- Not well localised
Describe acute non-cancer pain. Give examples.
- E.g. fracture, appendicitis
- Symptom of tissue injury or illness
- Usually nociceptive
- Occasionally neuropathic (e.g. scaitica)
Describe chronic non-cancer pain.
- E.g. chronic back pain, arthritis
- Injury may not be obvious
- Complex, may be mixed nociceptive and neuropathic
- Does not respond to usual drug treatment
Descirbe cancer pain and give examples.
- E.g uterine cervical cancer, breast cancer
- Features of acute and chronic pain - may be acute or chronic
- Often mixed nociceptive and neuropathic pain
- Usually gets worse over time if untreated
Define allodynia.
Allodynia refers to central pain sensitization (increased response of neurons) following normally non-painful, often repetitive, stimulation. Allodynia can lead to the triggering of a pain response from stimuli which do not normally provoke pain.
Define hyperpathia.
Hyperpathia is a clinical symptom of certain neurological disorders wherein nociceptive stimuli evoke exaggerated levels of pain. This should not be confused with allodynia, where normally non-painful stimuli evoke pain.
Define hyperalgesia.
Hyperalgesia is a condition where a person develops an increased sensitivity to pain.
Define nociception. How does it differ from pain perception?
How signal get from site of injury to the brain
Vs pain perception - how we “feel” pain
Not the same.
How does nocicpeption lead to pain perception?
What are the 4 main steps in pain phsyiology?
- Periphery
- Spinal cord
- Brain
- Modulation
What are the main peripheral pain receptors?
A-delta C nerve fibres
Describe the physiology of pain in the periphery.
- Tissue injury
- Release of chemicals
- Stimulation of pain receptors (nociceptors)
- Signal travles in A-delta C nerves to spinal cord
Descirbe pain perception in the spinal cord.
- Dorsal horn is the first relay station
- •Aδ or C nerve synapses (connects) with second nerve
- •Second nerve travels up opposite side of spinal cord
How does meditation reduce pain?
Descending inhibition is increased
Describe pain perception in the brain.
- Thalamus is the second relay station
- •Connections to many parts of the brain
- –Cortex
- –Limbic system
- –Brainstem
- •Pain perception occurs in the cortex
How does modulation affect pain perception?
Descending pathway from brain to dorsal horn
Usually DECREASES pain signal
Why is nocebo?
Nocebo - when you tell someone that the treatment will not work. either an effective intervention that should work but doesn’t or other way around.
What is the distribution of neuropathic pain in diabetes?
Glove and stocking distribution
What are some pathological mechanisms causiing pain?
- Increased receptor numbers
- Abnormal sensation of nerves - peripheral and central
- Chemical changes in the dorsal horn
- Loss of normal inhibitory modulation
Name some non-drug treatments for pain.
Physical
- –Rest, ice, compression, elevation
- –Surgery
- –Acupuncture, massage, physiotherapy
•Psychological
- –Explanation
- –Reassurance
- –Counselling
List some different types of analgesics.
- Simple analgesics
- Paracetamol (acetaminophen)
- Anti-inflammatory medicines (diclofenac, ibuprofen)
- Opioids
- Mild - codeine
- Strong - morphine, pethidine, oxycodone
- Other analgesics
- Tramadol
- Tricylic antidepressants (e.g. amitriptyline)
- Anticonvulsants (e.g. gabapentin)
- Ketamine
- Local anaesthetics
- Clonidine
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Which treatments for pain work on periphery?
- •Non‐drug treatments
- –Rest, ice, compression, elevation
- Anti-‐inflammatory medicines
- Local anaesthetics
Which pain tretaments act on the spinal cord?
- •Non‐drug treatments
- –Acupuncture, massage
- Local anaesthetics
- •Opioids
- •Ketamine
Which pain treatments act on the brain?
- •Non-‐drug treatments
- –Psychological
- •Drug treatments
- –Paracetamol
- –Opioids
- –Amitriptyline
- –Clonidine
What are the advantages and disadvantages of paracetamol?
- •Advantages
- –Cheap, safe
- –Can be given orally, rectally or intravenously
- –Good for: Mild pain (by itself)/Mod-‐severe pain (with other drugs)
- •Disadvantages
- –Liver damage in overdose
What are the advantages and disadvantages of anti-inflammatory medicines?
- •Aspirin, ibuprofen, diclofenac•
- Advantages
- –Cheap, generally safe
- –Good for nociceptive pain
- •Best given regularly with paracetamol
- •Disadvantages
- –Gastrointestinal and renal side effects
What are the advantages and disadvantages of codeine?
•Advantages
- –Cheap, safe
- –Good for mild-‐moderate acute nociceptive pain
- •Best given regularly with paracetamol
•Disadvantages –Constipation
- –Not good for chronic pain
- –Misunderstandings about addiction
When is addiction to pain drugs most common?
When the pain is chronic non-cancer pain
(rar in acute/cancer pain)
What are the advanatges and disadvantages of morphine?
- •Advantages
- –Cheap, generally safe
- –Can be given orally, IV, IM, SC
- –Effective if given regularly
- –Good for:
- •Mod-‐severe acute nociceptive pain (e.g. post-‐op pain)
- •Chronic cancer pain
- Disadvantages
- –Constipation
- –Respiratory depression in high dose
- –Misunderstandings about addiction
- –Controlled drug
What method of administration will cause morphine to have the strongest effect?
Oral dose is 2-3 times stronger than IV/IM/SC dose
Because of liver first-pass metabolism
What are the advantages and disadvanatges of pethidine(meperidine)?
- Can be good for severe acute nociceptive pain but has more disadvantages than morphine
- Disadvantages
- –Also a controlled drug
- –Must be given more frequently than morphine
- –Breakdown product (norpethidine) can cause convulsions
- –Not good for chronic pain
What are the advanatges and disadvanatges of tramadol?
- •Weak opioid effect plus inhibitor of serotonin and noradrenaline reuptake (modulation)
- •Advantages
- –Less respiratory depression
- –Can be used with opioids and simple analgesics
- –Not a controlled drug
- •Disadvantages
- –Nausea and vomiting
What are the advantages and disadvantages of amitriptyline?
- •Tricyclic antidepressant (TCA)
- •Increases descending inhibitory signals
- •Advantages
- –Cheap, safe in low dose
- –Good for neuropathic pain
- –Also treats depression, poor sleep
- •Disadvantages
- –Anti-‐cholinergic side effects (e.g. glaucoma, urinary reten9on)
Give 3 examples of anticonvulsant drugs? Why are they good for pain?
Reduce hyperexcitability in the spinal cord because they increase membrane stability
- Carbamazepine (Tegretol)
- Sodium valproate (Epilim)
- Gabapentin (Neurontin)
What pain are anticonvulsants good for?
Neuropathic pain
Compare the effectiveness of these drugs in different types of pain.
- Paracetamol
- NSAIDs
- Codeine
- Morphine
- TCAs
- Anticonvulsants
What is complex regional pain syndrome(CRPS)?
- Complex regional pain syndrome (CRPS) is a condition that causes severe pain which won’t go away.
- It usually affects just one arm or leg and often follows an earlier injury to the limb. However, the body’s reaction to the injury is much stronger than usual and may affect more of the limb than the original injury did.
This is usually following minimal tissue injury. A type of neuropathic pain.
Nociceptors may respond to
Pain, pressure, cold and heat
What is the normal morphine dosage?
10mg (oral morphine) every 1-2hours in moderate to severe pain
What is the RAT approach to pain management?
- •Recognize
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•Assess
- –Severity?
- –Type?
- –Other factors?
-
•Treat
- –Non-‐drug treatments
- –Drug treatments
What is the advanatge of ketamine?
It is cardiostable and doesn’t cause much respiratory depression
Therefore it is useful as anaesthetic in war e.g. ofr amputation as it causes dissociation
How do you measure severity of pain?
- Helps guide treatment
- •Methods
- –Verbal (e.g. mild, moderate, severe)
- –Numerical
- •0 (no pain) to 10 (worst pain imaginable)
- –Visual
- •Visual Analogue Scale (VAS)
- •“Faces” pain scale
What shoud a GP do for acute back pain?
Refer patient to physiotherapist
What is the typical paracetamol dosage?
0.5-1g every 4-6 hours and max 4g/day
IV and oral dosage is the SAME
What is the WHO pain ladder used for?
Commonly used for cancer pain
What is the normal ibuprofen dosage?
300-400mg 3-4 times/day
How do you treat neuropathic pain?
- –Traditional drugs may not be as useful
- –Use other drugs early
- •Amitriptyline
- •Gabapentin / carbamazepine
- –Don’t forget non-‐drug treatments
How do you treat mild/moderate/severe nociceptive pain?
- Mild - paracetamol (+/- NSAID)
- Moderate - paracetamol (+/- NSAID) + codeine
- Severe - paracetamol (+/-NSAID) + morphine
