Pain and analgesia Flashcards
What is the definition of pain?
unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
What is chronic pain?
pain that persists beyond the normal healing time or pain that persists in conditions where healing has not or will not occur
What is the difference between acute and chronic pain?
acute: obvious cause, relatively short duration, protective mechanism, easier to tx
chronic: multiple causes, persists after healing, non adaptive mechanism, often refractory to tx
What are the 3 types of pain?
nociceptive
inflammatory
maladaptive-pathological
What is nociceptive pain?
noxious stimuli activate neural receptors
What is inflammatory pain?
response of immune system to injury or infection
What is maladaptive-pathological pain?
amplification of pain, peripheral and central hypersensitization
What is the transduction pain pathway?
noxious stimulus is converted to electrical signal at a nociceptor
What is the transmission pain pathway?
transmission of nerve impulse along the nerve fiber to dorsal horn of spinal cord
What is the modulation pain pathway?
modulation of incoming pain at various CNS sites
What are the fiber systems that transmit pain impulses?
myelinated ao fibers: fast sharp well localised pain,fast conduction velocity
unmyelinated c fibers: slow dull poorly localised/visceral pain, slow conduction velocity
What is the gate control theory?
there are thought to be gates at the spinal cord, if these can be closed the pain cant be transmitted to the brain
What is hyperalgesia?
when peripheral sensory nerves impulses are amplified by the spinal cord
get confused and touch can feel like pain
What is part of the pain matrix?
primary and secondary somatosensory cortex, insular, anterior cingulate cortex and prefrontal cortex, thalamus
What is the role of the descending pathways in pain?
inhibitory and facilatory pathways
project to dorsal horn and inhibit pain transmission
What are the 4 tiers of descending inhibition (blocking pain)?
cortex and thalamus
prei-aquductal grey matter in midbrain
nucleus raphe magnus in pons, rostral medulla
medulla oblongata, spinal cord
What are the neurotransmitters involved in the descending pathways for inhibition of pain?
mainly: noradrenaline and serotonin
alose: dopamine, endocannabinouds, GABA, glycine, tonic control
What is central sensitisation?
sensitisation of nerves in the spinal cord and brain
amplification, facilitation of synaptic transfer from the periphery
What is the trigger and key role of central sensitisation?
trigger: intense nociceptor input
key role: nmethyldaspartate NMDA receptors
What is peripheral sensitisation?
injury/inflammation of tissue causing alterations of the chemical environment of the peripheral nerve terminal = activation/sensitisation
What is hyperalgesia?
increased sensitivity to a normally painful stimulus
How does hyperalgesia come about?
occurs at site of injury due to the inflammatory mediators
activation/sensitisation of nociceptors
spreads to surrounding non-injured tissues due to spinal cord events (central sensitisation)
What is allodynia?
painful response to a normally innocuous stimulus
mechanical receptors recruited to relay pain info
What are the ideal characteristics of a pain assessment tool?
discriminate presence or absence of pain
evaluate both the sensory and emotional aspects of the conditiion
evaluate pain in different contexts or at least clearly state the possible limitations
be as simple as possible, requiring minimal training and instrumentation
What are the 3 domains of the psychological state of pain?
sensory-discriminatory: intensity, location, duration of pain
affective motivational: emotional, unpleasantness and aversive aspects
cognitive-evaluative: evaluation upon quality of life
What are physiological and neuroendocrine markers for pain?
HR
RR
BP
circulating stress hormones
What is an algometer?
pressure testing device to determine pain in a quantitative way
What are the subjectives measure of pain?
behavioural assessment!
body posture and activity
locomotor activity
vocalisation
altered facial expression
appetite
response to manipulation
urinary and bowel habits
physiological signs
anxiety
What are the unidimensional pain scales?
simple descriptive scales
numerical rating scale
visual analog scale
Why do we use pre-emptive analgesia?
prevention or minimization of pain by the dministration of analgesics before the production of pain or the induction of noxious stimulus (surgery) if pain already exists
decreased need for follow up meds
What is multimodal analgesia?
administration of multiple drugs that act by different mechanisms of action to produce the desired analgesic effect
What are pharmacological interventions that provide analgesia?
opioids
nsaids
local anaesthesia
alpha 2 adrenergic agonist
ketamine
tramadol
gabapentin
amantadine
tricyclic antidepressants
maropitant
biphosphates
What are non pharmacological modalities that can provide an analgesic effect?
weight optimization
acupuncture
physical rehabilitation
nutrition amanagement
thermal modification
environement modification
chiropractic care
homeopathy
surgical intervention
What are opioids?
general term that refers to any naturally occuring, semi-synthetic and synthetic substance with morphine like activity