Pain Flashcards
What is the definition of pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
What are two main types of pain?
- Immediate pain (A delta)
- Persisting pain (C fibres)
How can diabetes cause neuropathic ulcers?
- Through peripheral neuropathy (loss of pain fibres)
- Damage to toes for example, will continue, ulcers can form which can become infected
- Poor vascular supply will extrapolate the issue
Where is the nerve cell body located in the nociceptor cells?
Dorsal Root Ganglion
At what speed do A delta fibres carry pain signals?
2 - 10 m/s
At what speed do C fibres carry pain signals?
1 m/s
WHat nociceptor fibres are unmyelinated?
C fibres
What type of pain is transmitted through A-delta fibres?
Sharp, localised
What type of pain is transmitted through C fibres?
Dull, throbbing, diffuse pain
What type of fibres are the majority of nociceptors?
C fibres
What types of stimuli do A-delta fibres respond to?
Extremes (not usually visceral)
Do nociceptors adapt?
No - in fact if anything they do the opposite - become more intense
What are the 4 categories of the physiology of pain?
- Transduction (stimulus translated into action potential)
- Transmission (movement of AP from periphery centrally to brain)
- Modulation (can down or up modulate the pain)
- Perception (conscious acknowledgement of pain)
What can cause a transduction of pain (what are the noxious stimuli)?
- Heat: >45deg or less than 15deg
- Chemical: K+, ATP, Bradykinin, histamine, Substance P
- Mechanical
What is primary hyperalgesia?
The recruitment of ‘sleeping’ C fibres
What does polymodal mean?
Responding to several different forms of sensory stimulation (as heat, touch, and chemicals)
- Such as in nociceptors
What substances can cause an increase in sensitization of nociceptors?
- Prostanoids
- Leukotrienes
- Substance P
- CGRP
- Glutamate
“Sensitizing soup”
What substances can activate nociceptors?
- K+
- H+
- Serotonin (5-HT)
- Bradykinin
- Histamine
Where do the primary afferent pain fibres synapse?
Dorsal horn
What are the excitatory neurotransmitters between 1st and 2nd order neurons?
- Glutamate (mainly)
- Substance P
- CGRP
What does glutamate bind to?
- AMPA (mainly)
- NMDA
- G-protein couple receptors
What fibres compose the neospinothalamic tract?
A delta fibres
What fibres compose the paleospinothalamic tract?
C fibres
Where do neospinothalamic tract fibres terminate?
Ventral posterior lateral nucleus
Where do paleospinothalamic fibres terminate?
Dorsomedial and intra laminar areas
What are the inhibitory substances of the dorsal horn?
- GABA and glycenergic interneurons
- Descending inhibition PAG-RVM-DH
- Endogenous opioids
Describe the GAte Control Theory? (rubbing to make a pain better)
Mechanoreceptor fibres synapse on inhibitory neurons of nociceptor fibres
- This allows A beta fibres to synapse on the target cell in dorsal horn
What can the gate control theory be used clinically for?
- TENS (transcutaneous electrical nerve stimulator)
- Used often in early stages of labour
- Patient has control over frequency of pain
- 2 electrodes on skin set up buzzing sensation modulates pain going into dorsal horn
What system elicits an autonomic response to pain?
Reticular system
What system links perception of pain with mood?
Limbic system
What do visceral nociceptors respond to distension or ischaemia?
Visceral nociceptors
What do visceral nociceptors converge on to give ‘referred’ pain?
Second order neurons with somatic input
What are some associated autonomic features of pain?
- Sweating
- Pallor
- nausea
- Tachycardia
- Hypertension
WHat can prevent and prepare for pain?
- Anticipation and simple adjustments (e.g. ICE)
- Distraction
- Education
- Challenge misconceptions
- Ametop, EMLA
- Re-brand tell patient they may be tender e.g instead of painful
- Patient control “raise hand if want to stop”
What are pain scoring systems scored from?
0 - 15 (above 10 being extreme pain)
What medications can be used to treat step 1 (mild pain)?
Simple analgesics
What medications can be used to treat step 2 (moderate pain)?
Mild opioids (e.g codeine, tramadol, continue simple analgesics)
What medications are used to treat step 3 (severe pain)?
Strong opiods
(e.g morphine)
Continue simple analgesics
What other medications can be added on at any pain stage on the WHO ladder?
Medications for neuropathic pain (e.g amitriptyline, gabapentin)
What was the WHO pain ladder developed to treat?
Cancer pain (nociceptive pain) (emphasises oral treatment)
What is neuropathic pain?
A pain arising as a direct consequence of a lesion or a disease affecting the somatosensory system
- Shooting/stabing
- Spontaneous and evoked pains
- Allodynia
- Common (3-18%)
- Challenge to manage
What is the most common causes of neuropathic pain?
- Traumatic (phantom limb pain)
- Diabetic neuropathy
- Posthepatic neuralgia
- Trigeminal neuralgia
- Post-stroke pain
What can be used to treat neuropathic pain?
- Gabapentin
- TCAs
- Anticonvulsants
What can be seen on examination in neuropathic pain?
changes in colour and sensation
How long does pain have to persist for it to be deemed chronic?
12 weeks
What is thought to be responsible for the neuroplasticity behind chronic pain?
- Prolonged inflammatory response results in decreased pain threshold in primary afferents
- Increased production of substance P and CGRP
- Recruitment of NMDA receptors (wakes up WDR, wind up phenomenon)
- Changes in gene and receptor expression in DRG and dorsal horn neurons
What is the fear-avoidance model?
- If patient is fearful of pain (something may be underlying it)
- Patient will be more negatively affected by it and it will disable them more than an ordianry person
- Constant negative - downward spiral
What are the non-modifiable risk factors for chronic pain?
- Female
- Age
- Genetic predisposition
- lower socio-economic status
- Occupational factors
- History of abuse
- Compensation
What are the modifiable risk factors for chronic pain?
- Past experience of pain (that site and others)
- Anxiety and depression
- Catastrophizing beliefs
- Surgical approach
- Attitude
- Communication
What are complex regional pain syndromes?
- Severe continous neuropathic pain
- Abnormal sensation
- Vasomotor change
- Sudomotor change
- Motor / trophic change
- Regionally restricted e.g. hand
- Disproportionate to the trauma
What can complex regional pain syndrome show on examination?
- Brawny discolouration
- Shiny skin
- Cyanotic fingers
- Brittle ridged fingernails
What is the budapest criteria?
Diagnoses complex regional pain syndrome
- Patients must report continuing pain disproportionate to the trauma
- Patients must report at least one symptom in three of the four following categories (sensory hyperalgesia and/or allodynia, vasomotor, sudomotor oedema, motor/trophic weakness)
- Patients must display one sign in two of the categories above
- Signs and symptoms must not be better explained by another diagnosis
