Pain Flashcards
What is pain?
Pain is the feeling or perception of irritating, sore, stinging, aching, throbbing, miserable, or unbearable sensations arising from a part of the body.
What is the sensory process for pain?
Nociception is the sensory process that provides the signals that trigger pain.
What is Congenital Analgesia?
The inability to feel pain from birth
Where are nociceptors found?
Nociceptors are found in the periphery as simple free nerve endings.
Where do peripheral nerve fibers terminate?
Peripheral nerve fibre branches & terminates as naked, unmyelinated endings in dermis.
What is the process of pain and hyperalgesia?
Tissue damage and inflammation triggers release of substances e.g prostaglandins, bradykinin and histamine that can sensitize peripheral nociceptors and induce hyperalgesia.
What is hyperalgesia?
Abnormally heightened sensitivity to pain.
What are the types of nociceptors?
Transduction of nociceptive stimuli occurs in the free nerve endings of unmyelinated ‘C’ fibres and thinly myelinated ‘Ad’ fibres.
What are the different modalities that nociceptors respond to?
Mechanical: respond to strong pressure.
Thermal: respond to burning heat / extreme cold.
Chemical: respond to histamine or other chemicals
Most nociceptors are polymodal and respond to what?
Mechanical, thermal & chemical stimuli.
What is the use of microneurography?
To see the distribution of nociceptors on the skin
What is the process of microneurography for comparison of thermoreceptor and nociceptor?
Thermal stimuli applied to receptive field of cutaneous thermoreceptor and nociceptor
B. Record afferent firing in response to incremental temperatures
C. Graph plotting afferent firing frequency versus temperature
What type of fibres do thermal and mechanical nociceptors have?
Aδ fibres (myelianted)
What type of fibres do polymodal nociceptors have?
C fibres ( unmeyelinated)
What is the general prinicpile of large diameter fibres?
Large diameter, rapidly conducting afferents (I/II) associated with low threshold mechanoreceptors.
What is the general prinicpile of small diameter fibres?
Small diameter, slow conducting afferents (III/IV) associated with nociceptors and thermoreceptors.
What is the characteristic of 1st pain?
Fast A-delta fibres Sharp or prickling Easily localised Occurs rapidly Short duration Mechanical or thermal nociceptors
What is the characteristic of 2nd pain?
Slow C-fibres Dull ache, burning Poorly localised Slow onset Persistent Polymodal nociceptors
How are the role of each sensory afferent in pain perception investigated?
It is possible to selectively anaesthetise C fibres and A delta fibres to dissect out the role of each sensory afferent in pain perception
What is the role of perception of nociception that is small and myelianted and one that is unmyelianted?
Small and myelinated –> sharp pain
Unmyelianted –> burnign pain
What is the route of nociceptive fibres?
Nociceptive fibres have their cell bodies within the dorsal root ganglion.
Afferent terminals enter the dorsal horn and travel up/down a short distance within the Zone of Lissauer.
Afferent terminals synapse onto neurones within the superficial laminae of the dorsal horn.
Principle areas innervated by nociceptor afferents are lamina I and lamina II (substantia gelatinosa).
How is nociceptive input from viscera and skin detected?
Nociceptive afferents from internal organs e.g. viscera and the skin enter spinal cord through common routes and target overlapping populations of spinal neurons
This ‘cross-talk’ accounts for referred pain whereby visceral pain is perceived as having a cutaneous source by the sufferer.
What is the referred pain of angina?
Pain is localised by the patient to the upper chest wall and the left arm
Where is referred pain for appendicitis at early stages ?
Pain is referred to the abdominal wall around the navel.
Pain afferent release what excitatory neurotransmitter?
Glutamate
What is the important neuropeptide in pain afferents?
Substance P
What type of pathway is the ascending pain pathway?
Contralateral pathway
What are the 3 components of the ascending pain pathway?
Lateral (neo-) spinothalamic tract.
Spinoreticulothalamic tract
Anterior spinothalamic tract to the reticular formation and
periaqueductal grey matter
What is dissociated sensory loss?
A unilateral spinal lesion will produce sensory loss of touch, pressure, vibration and proprioception below the lesion on the same side.
Diminished sensation of pain below the lesion will be observed on the opposite side.
Give a example of a syndrome where dissociated sensory loss occurs?
Brown-Sequard syndrome
What type of scan can you see pain?
PET scan
What is the process of pain and temperature from the face and head?
Trigeminal System:
(5th Cranial nerve)
Small diameter afferents descend in the spinal trigeminal tract to the brain stem.
Synapse with second-order sensory neurons in the pars caudalis.
Axons then ascend contralaterally to thalamus in the trigeminothalamic tract (also called the trigeminal lemniscus).
Projects to cortex via the ventral posteromedial nucleus.
What is phantom pain?
Pain and touch sensations with no sensory inputs
What are features of chronic pain and pathological pain?
Increased pain (hyperalgesia) or touch -evoked pain (allodynia)
In who’m is phantom pain usually seen in?
50-80% of amputees
pathological pain
A possible link between any pain existing pre-amputation i.e. acute injury or chronic pain
What is the possibly causes of phantom pain and is there any treatment?
Aetiology unclear
May be result of cortical re-organization in the ‘virtual’ body maps of thalamus and cortex
In phantom limb patients, maps distorted such that stroke on ‘face’ felt on missing limb
Highly resistant to treatment
What is central sensitization?
Is a condition of the nervous system that is associated with the development and maintenance of chronic pain
What causes central sensitization?
Permanent change in the synaptic structure of the dorsal horn
What is a function of opoid?
Presynaptic inhibition
GIve example of acute pain?
skin abrasions deep tissue injury postoperative dental superficial burn labour
Give examples of chronic pain?
inflammatory pain neuropathic pain neuralgias musculo-skeletal pain amputation/phantom visceral cancer migraine
What can hyperalgesia be?
A reduced threshold for pain
An increased intensity of painful stimuli
Spontaneous pain
What occurs in hyperalgesia?
Nociceptors normally respond to stimuli which damage tissue.
However, tissue that has already been damaged or inflamed is unusually sensitive.
What doees the gate theory of pain explain?
This theory explains why pain can be reduced by stimulating mechanoreceptors e.g. rubbing your knee after falling over.
Give example of opiate receptors?
mu, kappa and sigma
What is Dysaesthesias ?
unpleasant abnormal sensations
What is Allodynia ?
Pain in response to non painful stimuli
What is nociceptive pain?
Caused by actual tissue damage
and painful stimuli at nociceptors
Can be subdivided by its:
- Location
- Quality / character
What are the benefits of acute pain?
Part of trauma response
Protective–> avoid further damage
Learning experience
What is the adverse effects of acute pain?
Humanitarian issues
Cardiovascular stress
Respiratory compromise
Hypercoagulation!
What is the first analgesia in the analgesia ladder?
Acetaminophen
Aspirin
NSAIDs
COX-2 inhibitors
What is the second analgesia in the analgesia ladder?
Codeine
Dihydrocodeine(Propoxyphene)
Tramadol
What is the third analgesia in the analgesia ladder?
Morphine
Fentanyl
Hydromorphone
Buprenorphine
Methadone
what is the main use of non opoid analgesia?
Efficacy in acute pain management
and control of nociceptive pain
Where do NSAIDs/COX-2 inhibitors act mainly?
Peripherally white paracetamol is more central activity
Where do opoid analgesia mainly act?
Presynaptically pain signal
transmission is reduced
- Postsynaptic membrane is hyperpolarised, decreasing the probability of action potential
generation
When do you not give opoids?
Renal failure
Do not use morphine or codeine
sedative metabolites accumulate
What is a epidural analgesia?
Epidural analgesia is a specialised technique of pain management. It is obtained by administering drugs directly into the epidural space. An epidural catheter is usually placed to allow repeated doses or an infusion of the drug to be given
When is epidural analgesia used?
Postoperatively: thoracic, abdominal, groin/perineal, lower limb surgery – Labour pain – Chronic pain
What are the benefits of epidural analgesia?
High quality pain relief • Improved pulmonary function • Reduced sepsis and chest infection • Reduced cardiac morbidity • Reduced vascular graft failure • Reduced incidence of deep venous thrombosi
Where is the epidural space? What does it contain?
Potential space –> Between dura mater and the wall of the vertebral canal.
•
Composed of connective tissue, fat and blood vessels and nerve roots
Tissue in folds
What is Neuropathic pain?
Spontaneous pain and hypersensitivity
to pain in association with damage to,
or a lesion of, the nervous system
Give examples of neuropathic pain?
Post herpetic neuralgia – Painful diabetic neuropathy – Trigeminal neuralgia
Post traumatic / post operative
What is neuropathic pain assoicated with?
Intense pain that may be accompanied by other pain phenomena
Often persistent or recurrent
Associated with severe comorbidity and poor quality of life
What is the Features suggesting 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
How do you measure pain quality?
McGill Pain Questionnaire
MPQ
What is the advantages of McGill Pain Questionnaire
(MPQ)?
Well validated
Quality assessed
What is the disadvantages of McGill Pain Questionnaire
(MPQ)?
Time consuming
Insensitive to small
change in intensity
What are the Drug Therapy for neuropathic pain?
NSAIDs - poor
Antidepressants
Anticonvulsants
Opioids
Membrane stabilising drugs
Topical drugs
What are the Non medical management of Chronic Pain?
Models of pain modulation
Psychological assessment
Management implications:
Cognitive behavioral therapy
Stress management
Attention/distraction techniques
