Pain Flashcards
Definition of pain
Unpleasant sensory or emotional experience associated with actual or potential tissue damage
Classification
Acute
- noxious signally from recently damaged tissue
Chronic
- last or recurs for 3months +
- Subclassified
- chronic primary
- chronic cancer related
- chronic post-surgical
- chronic neuropthic
- chronic headache
Assessing acute pain
History - SOCRATES
Examination
Investigations
Assessment tools
- numerical rating scales
- visual analogue
- verbal ratiging
- facial pain scale (pads)
Assessing chronic pain
As above
Psychosical - sleep, mood, function, relationships
treatments received
ideas, concerns, expectations
Chronic pain assessment tools
- Mcgill pain questionnaire
- neuropathic pain scale
- brief pain inventory
Features of neuropathic pain
Spontaneous
- shooting, burning, electric shock, tingling, parasthesias
Allodynia
Hyperalgesia
Cancer pain
- Compression of surrounding tissues
- damage to nerves - neuropathic pain
- damage to other tissue - nociceptive pain
- consequence of treatment e.g. radiotherapy neuritis, chemo and peripheral neuropathy
- related problems - infection, hypercalcaemia
Opioids in cancer pain
most patients require long acting background e.g. MR or TD
1/6 daily dose for breakthrough
WHO analgesic ladder
Adjuncts if appropriate - gabapentin, steroid, bisphosphonates
Opiod side effects
CNS
- Sedation
- tolerance
- addiction
Resp
- reduced respiratory rate
- Hypoventilation
CVS
- bradycardia
GI
- Nausea
- Constipation
Genral
- itch
- immunosuppression
CRPS
Pain disorder characterised by limb pain with associated sensory, vasomotor, trophy, sudomotr changes. Usually precipitated by surgery or trauma
type 1 - injury to tissues or bones but no nerve injury
type 2 - nerve injury without transection
Clinical features
Continuous pain disproportionate to inciting event
1 sign in 2 categories
1 symptom in 3
no other diagnosis
Sensory - severe continious pain, glove and stocking, allodynia, hyperalgesia
Vasomotor - colour change, temperature change
Sudomotor - eodema, sweating
Motor - decreased range of movement, power
Management
MDT
Physio, OT, psycho
Pain specialists
pharmacotherapy weak evidence
- simple analgesics
- TCAs
- Gabapentinoids
- topical capsaicin
Tolerance, dependance, addiction
tolerance = requiring increasing doses of drug for same pharmacodynamic effect
dependance - adaption by which withdrawal of drug leads to unpleasant withdrawal symptoms
addiction - pattern of behaviours seeking reward from drug despite physical, social, psychological harm
Methadone
racemic mixture of R and S enantiomers
R-methadone has mu receptor agonism
S-methadone has anti-NMDA and help with withdrawal
bioavailability is 35-100%, liver metabolism, reanal excretion, protein bound
can cause prolonged QT
Assessing post-operative pain
Systematic approach
- reviewing anaesthetic chart, operation notes, surgical notes and drug chart
- history of pain e.g. SOCRATES
- Physical examination
DDX of pain post amputation
- Equipment issue (PCA) e.g pump failure, run out of drug, cannula tissued
- Surgical complications - bleeding, haematoma, infection
- stump pain
- PLP
Phantom limb pain
Perception of pain or discomfort in limb that is no longer there.
Common
1st week post-op
cramping, burning, shooting
Risk factors
- high pre-op pain
- emergency surgical intervention
- Bilateral amputation
- stump pain
Management
- multimodal
- gabapentinoids
- ketamine iv
- local - lignocaine patch, IV lignocaine, nerve catheter
Post herpetic neuralgia
chronic painful condition causing neuropathic pain within the sensory dermatome of a previous herpes zoster invection
Pathophysiology of PHN
- varicella zoster (chicken pox) remains dormant in DRG of sensory nerve
- herpes zoster (shingles) is a painful vesicular skin rash confined to a dermatome caused by reactivation of VZV
- sensory nerve becomes damaged by VZV leading to spontaneous discharge and neuropathic pain
Clinical features PHN
Pain 3 months + beyond shingles healing
- single unilateral dermatome, thoracic or V1
- burning stabbing, lancinating
- allodynia and hyperalgesia
Risk factors
- pyrexia during shingles
> 50
- female
- psychosocial risk e.g. anxiety
Management
- antivirals within 72hrs of shingles - no effect on PHN
- topical capsaicin and lignocaine patches
- gabapentinoids, TCA, opioids
Spinal cord stimulator
Implantable device using low voltage electrical stimulation to modulate nociceptive inputs into the spinal cord
MOA
- stimulations of dorsal column, dorsal roots
- inhibit nociceptive pathways - wide dynamic range neurones in dorsal horn, glial and immune cells
- activate descending pathways - GABA
- suppression of sympathetic fibres
SCS indications
- failed back surgery syndrome
- CRPS 1
- Chronic leg ischaemia
- diabetic neuropathy
- PLP
Persistent 6mo+ neuropathic or ischaemic pain resistant to conventional treatment, positive trial
insertion - theatre, sterile, epidural space, x-ray guidance, tuohy or surgical
tonic stimulation, burst suppression, high frequency
Management of SCS in periop
pre-op
- indication
- function
- pain team involvement
- deactivated (avoid interference, avoid risk of reporgrammin)
Intra-op
- positioning - mindful of device
- bipolar diathermy if possible
- if monopoly - avoid current path over SCS
- avoid neuraxial
post-op
- switch on
- pain team
NB. PPM and SCS - contraindicated (interference). deactivate in pregnancy
gate control theory of pain
account for physical and psychological influences on pain transmision
interneurones modulate synaptic transmission between primary and secondary
inhibitory interneurones close the gate (either pre-synaptically or post-synaptically)
activation of inhibitory interneurones by non-painful stimuli
practical - rubbing sore spot, TENS
Classification of trigeminal neuralgia
Classical
- women 50-60yrs
- neurovacqlar compression of the trigeminal nerve root near entry to pons resulting in local demyelination
- superior cerebellar artery, anterior inferior cerebellar artery, basilar artery
Seconary
- neurological disease such as MS, cerebellopontine angle tumours
Idiopathic
- no cause found
