Pain Flashcards
Definition of Pain
- unpleasant sensory and emotional experience
- associated with tissue damage
- international association for the study of pain, 1994
Types of Pain
Acute
- 3 months
- tissue damage
- single or recurrent episodes
- anxiety provoking
Chronic
- persists beyond normal healing time (IASP, 1986)
- no adaptive function
- recurrent and progressive
- depression link
Assessment:
Verbal Rating Scale
- unidimensional measure
- 4 point scale (no pain, mild, moderate, severe)
- number associated with adjective
- combine to create pain intensity score
- critique : assumes equal intervals between ranks
Assessment:
Visual Analogue Scale
- unidimensional measure
- score marks across line to represent pain intensity
- distance measured from start to mark indicates pain intensity
Strength - has ratio qualities
- high number of response outcomes
Critique - scoring time consuming
- no account for psychological factors
Assessment:
Numerical Rating Scale
- unidimensional measure
- 0 = no pain, 10 = worst pain possible
Strength - good validity
- easy to administer to wide variety of patients
Critique - no ratio properties
- Jensen and Karoly, 2002
Assessment:
McGill Pain Questionnaire
(Melzack, 1975)
- multidimensional measure
- measures 20 classes of words
- sensory (gnawing)
- affective (punishing)
- evaluative (intense)
- choose word from each subclass
- measure number and word combo (0 = no pain, 5 = excruciating)
Strength - able to discriminate between conditions
Weakness - confusion about word meaning
Early Theories of Pain
Plato
- pain peripheral and emotional response in the soul
Galen
- established anatomy of cranial and spinal nerves, brain the centre for sensitivity
Aristotle
- brain has no direct function in sensory processes
Hippocrates
- pain due to deficiencies/excess in one of four humours or fluids
Main and Spanswick, 2000
Specificity Theory
Von Frey, 1895
- stimulus-response, direct relationship between pain and injury
- painful stimuli picked up by receptors in the skin and transmitted to the pain centre in the brain
- intensity proportional to damage
Specificity Theory Critique
- pain without injury (tension headache, some back pain)
- pain disproportionate to injury (gall stone, kidney stone)
- pain after injury heals
- episodic analgesia (Beecher’s soldiers, 1959)
- phantom limb pain (explains acute not chronic pain)
Pattern Theories
Skevington (1997)
- excessive stimulation of the nerves creates patterns of nerve impulses
- summated in dorsal horns of the spinal cord and cause pain
- pain due to excessive stimulation of peripheral non specific receptors which is interpreted centrally as pain
- can lead to pain after I just had healed (Livingstone, 1943)
Pattern Theories Critique
Strength
- can explain chronic pain mechanisms
Critique
- does not consider complex experience of pain
- requires that stimuli triggering pain must be intense
Gate Control Theory of Pain
Melzack and Wall, 1965
Pain signal ⬇️ C fibres (throbbing, chronic) or A delta fibres (quick, intense) ⬇️ Laminae ⬇️ A beta nerve fibres (inhibitory neurone not activated) ⬇️ Spinal cord ⬇️ Brain
Gate Control Theory
Continued
- pain is a pathophysiological process
1. Pain receptors in skin transmit damage info to “gates” in the dorsal horns in the spinal cord
2. Psychological factors (at brain level) can activate nerve fibres taking info from brain to spinal cord - worry/ catastrophising; reduce endorphins and open pain gate
- positive; increase endorphins and close pain gate
- level of pain felt results in differing activation of both systems (Morrison and Bennett, 2006, Main and Spaswick, 2000)
Types of Pain Receptors
Myelinated a-delta (types 1 and 2) - light touch, mechanical and thermal - short lasting pain Unmyelinated c-fibres - slow conducting - dull throbbing pain A-beta fibres -tactile info related to touch - if site of injury actions by a-delta, a-beta activates and supersedes a-delta at spinal cord
Pain Receptor Actions
- a-delta and c-fibres transmit info to substantia gelatinosa in dorsal horn
- SG contains executory and inhibitory cells
- nerve impulses trigger chemical release to SG that activates t-fibres
- a-beta inhibits t-fibre activity
- balance of activity influence gate being open or closed
- a-fibres; info to hypothalamus and cortex
- c-fibre; info to limbic system, hypothalamus, ANS
- reticulospinal fibres - results of neural activity to spinal gating mechanism may cause chemical release to SG