Pain 2 Flashcards
What are the 2 types of pain as classified by duration?
1) Acute
2) Chronic
What are the 2 types of pain as classified by pathophysiology?
1) Nociceptive
2) Neuropathic
What are the main differences between acute and chronic pain?
Acute pain is associated with injury and resolves with healing of the underlying injury, it serves a protective function and assists wound repair
Chronic pain persists beyond the normal type of healing and is dissociated from tissue damage, it ceases to perform a protective function and is associated with considerable suffering
What is nociceptive pain?
Pain which is caused by actual tissue damage and painful stimuli at nociceptors
How is nociceptive pain regulated?
By the opioidergic system
Is it possible to get chronic nociceptive pain?
Yes - for example osteoarthritis, but chronic nociceptive pain may lead to neuropathic and mixed pain
What are the 2 main beneficial aspects of acute pain?
1) protective - avoid further damage
2) Learning experience
It is part of the trauma response
What are the 4 main adverse effects of acute pain?
1) Humanitarian issue
2) Cardiovascular stress
3) Respiratory compromise
4) Hypercoagulation
For what 2 reasons is it very difficult to measure pain?
1) It is a synthesis of several observations eg. intensity, quality etc
2) How it is perceived is relative to distress of person eg. acid reflux in normal 43 year old compared to in a 43 yr old with strong family history of IHD may be perceived as more severe in latter
What are the 5 factors associated with changes in pain perception?
1) Anxiety
2) Depressed affect - if depressed pain is felt more strongly
3) Gender - socialisation/gonadotrophins
4) Circadian variation - pain worse in middle of night
5) Climatic conditions - MSK pain thought to be worse in cold
How can pain be assessed in patients?
Self reported - visual analogue score
Assess at rest and during movement
What are the 3 main steps in the analgesic ladder, when do you progress through the ladder?
Start at the bottom and progress if pain persists or is increasing
1) Non-opioid +/- adjuvant
2) Opioid for mild to moderate pain + non opioid +/- adjuvant
3) Opioid for moderate to severe pain + non opioid +/- adjuvant
Name 4 non opioid drugs?
1) Acetaminophen
2) Aspirin
3) NSAIDs
4) Cox-2 inhibitors
Name 3 opioids for mild to moderate pain?
1) Codeine
2) Dihydrocodeine
3) Tramadol
Name 5 opioids for moderate to severe pain?
1) Morphine
2) Fentanyl
3) Hydromorphone
4) Buprenorphine
5) Methadone
In what way do opioids act at 2 sites in the spinal cord?
1) Presynaptically pain signal transmission is reduced
2) Post synaptic membrane is hyperpolarised, decreasing the probability of an action potential being generated
NSAIDs and COX-2 inhibitors act mainly peripherally, which non opioid has central acitivity?
Paracetemol
What is the mode of action of NSAIDs?
Inhibition of cyclo-oxygenase - prostaglandin synthesis decreases
What are the 4 main side effects of NSAIDs?
1) GI irritation/bleeding
2) Renal toxicity
3) Potential drug-drug interactions
4) CV side effects (COX2)
What is the efficacy of NSAIDs?
Mainly act on nociceptive pain
What is the efficacy of opioids?
Mainly nociceptive pain - less effective in chronic states, only partially effective in neuropathic pain
What is the efficacy of paracetemol?
Analgesic and antipyretic effects, no anti inflammatory action
What is the mode of action of paracetamol?
Not fully understood - inhibits central prostaglandin synthesis
What is the main side effect of paracetamol?
Risk of toxic liver damage
What is the mode of action of opioid analgesics?
- Activate the endogenous analgesic system
- Stimulate receptors in the limbic system to eliminate the subjective feeling of pain
- Affect descending pathways that modulate pain perception
- Reduce ascending pain signal transmission in the spinal cord
What is the problem with large bolus analgesia?
Narrow range in which get analgesia without side effects - when only given as a large bolus then the plasma level fluctuates from pain to a level at which side effects occur rather than staying constantly within the plasma level range which has only analgesic effects
Name a method of avoiding large bolus analgesia and maintaining opioids within the optimum therapeutic range?
Patient controlled analgesia - small bolus and 5 minute lockout
What are the 6 main side effects of opioids?
1) Nausea
2) Vomiting
3) Constipation
4) Dizziness or vertigo
5) Somnolence
6) Dry skin, pruritus
What is the most serious potential adverse affect of systemic opioid analgesia?
Respiratory depression and hypoxia
What is the best early warning sign of respiratory depression with systemic opioids?
Progressive sedation
- not respiratory rate, not SpO2
What 2 opioids should not be used in patients with renal failure and why?
Morphine or codeine
Sedative metabolites accumulate
(Fentanyl or oxycodone are OK)
In patients with a history of substance abuse how should opioids be used?
Give what is required - use balanced analgesia
What is epidural anaesthesia?
Drugs administered directly into the epidural space
What are the 3 common uses of epidural anaesthesia?
1) Postoperatively: thoracic, abdominal, groin/perineal, lower limb surgery
2) Labour pain
3) Chronic pain
What are the 6 benefits of epidural anaesthesia?
1) High quality pain relief
2) Improved pulmonary function
3) Reduced sepsis and chest infection
4) Reduced cardiac morbidity
5) Reduced vascular graft failure
6) Reduced incidence of DVT
Where is the epidural space?
Between dura mater and the wall of the vertebral canal
What are the 5 areas of block in epidural anaesthesia?
1) High thoracic - upper chest
2) Low thoracic - middle trunk
3) Low thoracic/high lumbar - lower trunk and groin area
4) Lumbar - legs
5) Caudal - saddle region
What percentage of people with advanced cancer experience pain?
75%
What percentage of cancer patients control their pain with oral or sub cut opioids?
90% -the other 10% require complex management
What are the rough guidelines for use of morphine correctly?
1) begin with regular immediate release morphine (provide access morphine for breakthrough pain)
2) Review regular requirement by incorporating breakthrough dose into new 4 hourly dose
3) When stable convert to sustained release morphine (but still provide for breakthrough pain)
What type of cancer is a celiac plexus block used in?
Pancreatic carcinoma and upper abdominal neoplasia
At what part of the spinal cord do spinal opioids act at?
Dorsal horn of the cord
Which type of spinal opioid reaches the brainstem?
Lipophobic morphine
Which type of spinal opioid remains segmentally localised?
Lipophilic fentanyl
In what 5 ways can morphine be administered?
1) PO
2) IV
3) Epidural
4) Intrathecal
5) Intraventricular
What is neuropathic pain?
Spontaneous pain and hypersensitivity to pain in association with damage to or a lesion of, the nervous system, it is intense and may be accompanied by another pain phenomenon, often persistent and associated with severe comorbidity and poor quality of life
Give 5 examples of conditions which cause neuropathic pain?
1) Post herpetic neuralgia
2) Painful diabetic neuropathy
3) Trigeminal neuralgia
4) Pain after CVA
5) Post traumatic/post operative
What is thought to be the spinal mechanism behind neuropathic pain following surgery/ trauma?
Hyperexcitable spinal cord
Previously silent nociceptors start signalling following trauma
Have an expanded hyperexcitable dorsal horn with ne inputs
What is the supraspinal mechanism involved in neuropathic pain following surgery/trauma?
Remapping of the thalamus and cortex - this is associated with more pain
Regions of the cortex which prior to the surgery were receiving input and now are not, get confused by this and start manifesting pain
WHat are the 7 features suggesting neuropathic pain?
1) Pain different from normal everyday pain
2) Pain in the absence of ongoing tissue damage
3) Pain in an area of sensory loss
4) Paroxysmal or spontaneous pain
5) Allodynia (pain in response to non painful stimuli)
6) Hyperalgesia (increased pain in response to painful stimuli)
7) Dysaesthesia (unpleasant abnormal sensations - eg ants crawling on the skin)
What is the prevalence of neuropathic pain?
2-4% of population
What 3 psychiatric conditions are associated with neuropathic pain?
1) Depression
2) Anxiety
3) Insomnia
Name a questionnaire designed to measure pain quality?
McGill Pain questionnaire
What are the 2 advantages and 2 problems with the McGill Pain questionnaire?
Advantages = Well validated and quality assessed Problems = Time consuming, Insensitive to small change in intensity
Which type of pain medication acts on the brain?
Opioids
Which 4 types of pain medication act on the dorsal grey horn?
1) Opioids
2) Antidepressants
3) Anticonvulsants
4) Non-opioid analgesics
Name 2 types of pain medication which act in the periphery?
1) Topical analgesics
2) Non-opioid analgesics
What are the 5 possible drug therapies for neuropathic pain?
1) Antidepressants
2) Anticonvulsants
3) Opioids
4) Membrane stabilising drugs
5) Topical drugs
For what 3 types of pain are antidepressants (TCAs) effective?
1) Neuropathic pain
2) Complex regional pain syndrome
3) Tension headache
What is the mode of action of antidepressants - TCAs?
Inhibition of neuronal re-uptake of noradrenaline and serotonin 5-HT
What are the 6 side effects of TCAs?
1) Constipation
2) Dry mouth
3) Somnolence
4) Abnormalities in heart rate and rhythm
5) Insomnia
6) Increased appetite
Can antidepressants other than tri-cyclic agents be used for neuropathic pain?
No - serotonin uptake inhibitors are relatively ineffective
What are the modes of action of the anticonvulsants Gabapentin, Pregabalin, Carbamazepine in the treatment of neuropathic pain?
Gabapentin - binds to pre-synaptic voltage-dependent calcium channels
Pregabalin - interacts with special N-type calcium channels
Carbamazepine - blocks Na+ and Ca2+ channels
What are the 6 main side effects of anticonvulsants?
1) Sedation
2) Dizziness
3) Ataxia
4) Peripheral oedema
5) Nausea
6) Weight gain
Does the anticonvulsant Gabapentin work in both nociceptive and neuropathic pain?
Prevents neuropathic but not nociceptive pain in animal models
How is the anticonvulsant Gabapentin excreted?
Renally excreted
What does operant conditioning have to do with pain?
Whilst nociception may be the origin of a pain behaviour, if that pain behaviour is reinforced it is likely to occur even in the absence of nociception
What are the non medical approaches to managing chronic pain?
1) Cognitive behavioural therapy
2) Stress management
3) Attention/ distraction techniques
