Clinical Aspects of Pain Flashcards
What is the definition of pain?
How is it measured?
an unpleasant sensory and emotional experience associated with actual or potential tissue damange or described in terms of such damage
measurement is subjective
How is pain classified according to duration?
pain is either acute or chronic
What is acute pain associated with?
What type of pain is it usually?
What does it assist and resolve with?
associated with trauma or injury
usually nociceptive
- pain is proportional to magnitude of injury
- evolutionary protective function
- assists with wound healing
- resolves with healing
What is chronic pain?
What does it cause in the patient?
pain that persists past normal duration of tissue healing
(3 months)
may be dissociated from tissue damage
no obvious protective function and causes distress and suffering
What are the 3 pain classifications according to pathogenesis?
- nociceptive pain
- neuropathic pain
- psychogenic pain
What causes nociceptive pain?
it is caused by the presence of a painful stimulus on nociceptors
nociceptors in tissues send pain signals to the CNS
mechanisms involve endogenous opioids
What causes neuropathic pain?
it is initiated or caused by a primary lesion or dysfunction in the nervous system
damage to the nerve itself causes typical pain symptoms
it is often endogenous opioid independent
What causes psychogenic pain?
it is caused by the mental processes of the sufferer rather than by immediate physiological causes
What is the main difference between nociceptive and neuropathic pain?
What similarities do they have?
nociceptive pain:
- due to activation of nociceptors in tissues by a stimulus
neuropathic pain:
- due to damage to the nerve itself
both can be the underlying pathogenic mechanism for acute or chronic pain
both can appear together (e.g. back pain)
How is pain classified?
pain is multifactorial in nature
it can be primary nociceptive with injured/irritated somatic or visceral structure
it can be primary neuropathic with injury of a neural structure
it can have both nociceptive and neuropathic components
What are examples of primary nociceptive pain?
- osteoarthritis
- visceral pain
- headache
- ischaemic pain
- cancer pain / back pain (without nerve injury)
What are examples of primary neuropathic pain?
- peripheral back pain due to nerve injury
- trigeminal neuralgia
- HIV
- CRPS II
- phantom pain
- multiple sclerosis
- spinal cord injury
- post stroke
What are examples of pain including both a nociceptive and neuropathic component?
- chronic back pain
- nerve lesion / dysfunction
- nociceptive activation from ligaments, joints, muscles, tendons
- cancer pain with nerve infiltration
- CRPS I
- osteoporotic vertebral fracture
How is pain assessed?
What are the problems associated with this?
measuring absolute pain is a problem
pain is a construct:
- synthesis of several observations including intensity, quality, etc.
relative distress:
- e.g. acid reflux in healthy 42 yr old v. acid reflux in 42 yr old with strong family history of ischaemic heart disease
What are some factors associated with changes in pain perception?
- anxiety
- depressed effect
- gender - socialisation / gonadotrophins
- circadian variation
- climatic conditions
How is pain assessed in clinic usually?
it is self-reported by the patient using a visual analogue score
pain is assessed at rest and during movement
What is the adult acute pain intensity score?
a score of 0 - 3 that is used to assess pain intensity on movement
What is the natural history of acute nociceptive pain like?
How is it mediated?
the sensory experience of acute pain caused by a noxious stimulus is mediated by a specialised high-threshold sensory system - the nociceptive system
What are the beneficial consequences of acute pain?
- part of trauma response
- protective as it avoids further damage
- learning experience
What are the adverse consequences of acute pain?
- humanitarian issues
- cardiovascular issues
- respiratory compromise
- hypercoagulation
When should the WHO analgesia ladder be consulted?
in acute pain only
What are the 3 levels of the analgesia ladder?
- non-opioid +/- adjuvant
- pain persisting or increasing*
- opioid for mild to moderate pain + non-opioid +/- adjuvant
- pain persisting or increasing*
- opioid for moderate to severe pain + non-opioid +/- adjuvant
What types of analgesics are used at the first level of the analgesia ladder?
- acetaminophen
- aspirin
- NSAIDs
- COX-2 inhibitors
What type of analgesics are used at the second level of the analgesic ladder?
- codeine
- dihydrocodeine
- tramadol
What types of analgesics are used at the third and final stage of the analgesic ladder?
- morphine
- fentanyl
- hydromorphone
- buprenorphine
- methadone
How can nociceptive pain from tissue damage be subdivided?
somatic:
- affecting bones or soft tissues
visceral:
- affecting the gut and/or organs
What is the efficacy of NSAIDs like?
they are non-opioid analgesics
they mainly act on nociceptive pain
What is the mode of action of NSAIDs?
they inhibit the enzyme cyclooxygenase (COX)
this consequently inhibits prostaglandin synthesis
by inhibiting prostaglandins, this reduces tissue inflammation and pain
What are the stages involved in prostaglandin synthesis?
- cell membrane phospholipids are converted to arachidonic acid by phospholipase A2
- arachidonic acid is converted to PGG and PGH by cyclooxygenase
- PGG and PGH go on to form prostaglandins and thromboxane
Why are NSAIDs said to be ‘non-selective’?
they will inhibit both COX-1 and COX-2 enzymes in a ratio that varies from drug to drug
selective COX-2 inhibitors are more potent at inhibiting COX-2 enzyme
What are common side effects of NSAIDs?
- GI irritation / bleeding
- asthma
- renal toxicity
- potential drug-drug interactions
- cardiovascular side effects (COX-2)
- e.g. myocardial infarction, stroke, elevation of blood pressure
- use with caution on older patients with impaired renal function and heart failure
What are examples of weak and strong opioids?
weak opioids include tramadol and codeine
strong opioids include morphine and oxycodone
What is the efficacy of opioid analgesics like?
- mainly effective in acute nociceptive pain
- less effective in chronic states
- only partially effective in neuropathic pain
- they are mainly used in management of postoperative and cancer pain
What is the mode of action of opioid analgesics like?
- they 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 receptors do opioid analgesics primarily target?
opioids mainly act in the CNS and are agonists of morphine receptors
these are present in the brain and spinal cord
How does receptor activation by opioid analgesics in the limbic system affect pain?
receptor activation in the limbic system affects the emotional response to pain
the pain remains, but it does not hurt anymore
What does activation of morphine receptors in the spinal cord by opioid analgesics lead to?
hyperpolarisation of interneurones and a reduction in pain transmission
they can also act peripherally to block the transmission of pain signals before they reach the spinal cord
What are the main side effects of opioid analgesics?
- nausea
- vomiting
- constipation
- dizziness or vertigo
- somnolence
- dry skin, pruritus
What are some risks associated with opioid analgesics?
increased risk of respiratory depression, espcially in situations of overdose and concommitant use of CNS depressant drugs
What advice is given to patients to tackle constipation associated with opioid analgesics?
drink lots of fluid, eat fruit and fibre
a stool softener and stimulant laxative are often necesary
Why is it important to recognise respiratory impairment as a side effect of opioid analgesics?
it is complex and dangerous
it is linked to obstructive sleep apnoea
What is meant by patient-controlled analgesia (PCA)?
the patient controls the amount of medication they need to acheive pain relief
the amount of opiate required varies significantly among patients
What are the benefits to using patient-controlled analgesia?
by allowing the patient to titrate a desired plasma level of opiate, the chance of acheiving analgesia is enhanced
the likelihood of inadequate drug dosing or overdosing is decreased
side effects less likely
Typically what is the set-up for patient controlled analgesia with morphine?
1 mg bolus is given with 5 minute lockout
What is the main long term opioid side effect?
opioids have an immunosuppresant effect
this is mediated via opioid receptors on immune effector cells and in the central nervous system
possible effects on antimicrobial response and anti-tumour surveillance
What are 2 other long term opioid side effects?
- dose related impairment of both:
- hypothalamic-pituitary-adrenal axis
- hypothalamic-pituitary-gonadal axis
- leading to adrenal insufficiency and poor libido
-
opioid-induced hyperalgesia
- a patient on long term opioid therapy presents with increased pain
- managed by reducing the dose
How is cancer pain managed?
How many cancer patients experience pain?
75% of patients with advanced cancer experience pain
90% of patients are controlled with oral or s.c. opioid
10% require complex management
How should morphine be used correctly?
- begin with regular immediate release morphine (oromorph) 4 hourly
- provide access to morphine for breakthrough pain
- review regular requirement by incorporating breakthrough dose into new 4 hourly dose
- when stable convert ot sustained release morphine (MST / MXL) but still provide for breakthrough pain
What is the celiac plexus block?
it involves injection of 50 ml of absolute alcohol
it is used for pancreatic carcinoma and upper abdominal neoplasia
What is neuropathic pain?
What are examples?
spontaneous pain and hypersensitivity to pain in association with damage to, or a lesion of, the nervous system
- post herpetic neuralgia
- painful diabetic nephropathy
- trigeminal neuralgia
- pain after CVA
- post-traumatic / post-operative
How can neuropathic pain be subdivided?
it can be subdivided by its:
- location
- quality / character
What may neuropathic pain be accompanied by?
it is an intense pain that may be accompanied by other pain phenomena
- allodynia
- paraesthesia
- paroxysmal pain
How does neuropathic pain affect quality of life?
it is often persistent or recurrent
it is associated with severe comorbidity and poor quality of life
What features suggest neuropathic pain?
- pain different from normal everyday pain
- pain in absence of ongoing tissue damage
- pain in area of sensory loss
- paroxysmal or spontaneous pain
- allodynia
- hyperalgesia
- dysaesthesias
What is allodynia?
pain in response to non-painful stimuli
What is hyperalgesia?
increased pain in response to painful stimuli
What are dysaesthesias?
unpleasant abnormal sensations
“ants crawling on the skin”
What are the mechanisms of neuropathic pain?
C fibres die in response to a barage of acute pain
a previously silent nociceptor becomes acitve
a-beta fibres become connected to nociceptive dorsal horn interneurones
there is an expanded hyperexcitable dorsal horn with new inputs
What is the initial treatment for neuropathic pain>
a choice of one of:
- amitriptyline
- duloxetine
- gabapentin
- pregabalin
this is not used for trigeminal neuralgia
What should be done in neuropathic pain if the initial treatment is not effective?
offer one of the remaining 3 drugs and consider switching again if needed
When should capsaicin cream and tramadol be used in neuropathic pain treatment?
tramadol:
- used only if acute rescue therapy is needed
capsaicin cream:
- used for people with localised neuropathic pain who cannot tolerate oral treatments
WHat is spinal cord stimulation?
an established therapy that involves the delivery of energy to the spinal cord through electrodes in the epidural space
How does spinal cord stimulation work?
What is it typically prescribed for?
it delivers small electrical pulses to the pain sensing pathways of the spinal cord
it effectively altering the pain signals travelling to the brain
When is SCS usually prescribed?
for pain of the back, trunk or limbs
What are cannabinoids isolated from?
What are the 2 main ones that are used?
isolated from hemp
tetrahydocannabinol has a psychotropic effect
cannababidiol is non-psychotropic
What receptors do cannababidol (CBD) 1 and 2 act on?
CB1 - nervous system
CB2 - immune
What is the relevance of cannabinoids to chronic pain?
limited evidence for use in pallative care
no evidence to support use in chronic pain of non-cancer origin
harms probably outweigh the benefits
What is involved in the non-medical management of chronic pain?
- psychological assessment
- management implications
- cognitive behavioural therapy
- acceptance & commitment therapy
- stress management
- attention/distraction techniques
What are the four dimensions of pain conceptualized by Loeser?
nociception:
- activation of Ad fibres by potentially damaging energy on specialised nerve endings
pain:
- the input of the Ad and C fibres into the nervous system
suffering:
- the negative affective response to pain, generated by higher cortical processes
pain behaviours:
- any behaviours that indicate the presence of pain
- e.g. grimacing, taking medicines
How are the four dimensions of pain related?
the factors are not linearly related
i.e. some patients may have significant nociception with little suffering
some patients may have severe pain behaviours with little nociception
What is meant by “pacing”?
How should activity levels be increased?
pacing is knowing the baseline level of activity that you can complete before being in too much pain
- basing what you do on this plan
- doing a regular amount of activity on each day
- doing more than the minimum on a bad day
- doing less than the maximum on a good day
- working to gradually increase activity level from this baseline
What is pacing NOT?
- basing what you do on how you feel
- doing lots on a “good day” and doing nothing on a “bad day”
- taking things easy or giving up on things you want to do
