Pain Flashcards
Pain definition
Subjective sensation of nociceptive stimulus
TRP acronym
Transient Receptor Protein
TRP types
TRP v1
TRP M (‘M’ = menthol)
TRP v1
Chilli pain receptors
TRP M
Cold
Pain nerve fibre classification
C fibres
A delta
C nerve fibre qualities
Non-myelinated
Slower longer onset of pain
A delta nerve fibre qualities
Myelinated -
Quicker shorter onset of pain
Common pain nerve fibres in viscera
C
Common pain nerve fibres in skin
A delta
Pathway of pain signal - Pain cascade
Nerve ending impulse ->
Dorsal root ganglion (glutamate in synapse) ->
Decussates at level of spinal cord ->
Spinothalamic tract ->
Thalamus ->
Signal splits to multiple parts of the brain:
- Cortex
- Periaqueductal grey
- Nucleus Raphe Magnus
- Locus Coeruleus
Excitatory synaptic neurotransmitter
Glutamate
Inhibitory synaptic neurotransmitter
GABA
Gate control theory of pain site
Substantia gelatinosa
Nerve input to substantia gelatinosa
A delta pain fibre
A beta motor fibre
Periaqueductal grey via Nucleus Raphe Magnus
Locus coeruleus
Location of periaqueductal grey
Around 3rd ventricle to base of brain stem
Neurotransmitter for Nucleus Raphe Magnus
Serotonin
Neurotransmitter for Locus Coeruleus
Noradrenaline
Receptor present in substantia gelatinosa
NMDA
NMDA receptor qualities
Ionotropic receptor (not g protein coupled)
Glutamatergic
Particularly permeable to Calcium ions (and Sodium)
How does Magnesium inhibit NMDA receptor
Magnesium and 2+ charge (same as Calcium) but is larger in size so does not pass Magnesium
Electrochemical gradient attracts Magnesium but blocks receptor
Competes with calcium but does not permeate
Use dependant blockade of NMDA receptors
Action of intravenous Lidocaine at non cardiotoxic doses
NMDA receptor antagonist
Ketamine mode of action
NMDA receptor antagonist
Methods to reduce pain in peripheral nerve tissue
Regional block
Reduce size of incisions
Anti-inflammatories (NSAIDs, Dexamethasone)
Drugs
Types of opioid receptors
Mu opioid receptor
Kappa opioid receptor
Delta opioid receptor
Opioid receptor qualities and action
Pre-synaptic G coupled metabotropic receptor
Gi (inhibitory)
Reduces cyclic AMP action
Reduces voltage gated calcium channel action
Location of action of opioid receptors
Spinal level - receptors in substantia gelatinosa
Further in pain cascade - inhibitory action on locus coeruleus
Mode of action of clonidine
Alpha 2 receptor agonist
Effects of clonidine
Anxiolytic - reduced sympathetic drive
Analgesia - not 100% know but possible reduced noradrenaline action (eg from locus coeruleus
Analgesia option which effects Nucleus Raphe Magnus and Locus coeruleus
Tricyclic antidepressants - Amitriptyline
Duloxetine
Mixed SNRI effects
Plane block definition
Anaesthetise ‘plane’ / area rather than specific nerve
More conducive to catheter insertion as less risk than when placed directly to nerve
Approach to regional block pain calls
Check block area with ethyl chloride spray
Does level of block need to increase (more volume, lower concentration)
Does level of analgesia need to increase (less volume, higher concentration)
