week 4 - pain (copy)

define pain

• unpleasant or discomfort

• actual or potential tissue damage

• interactions btw physical, cognitive, spiritual, emotional, environmental

• subjective

pain threshold

• point at which stimulus is perceived as pain

• lower in children 5-18yo

• higher as you age due to:

  • peripheral neuropathies

  • changes in skin thickness

  • cognitive impairment

pain tolerance

• most intense pain an individual can endure before initiating overt responses

• 10 on pain scale

• decrease as you age:

  • decreased inhibitory modulation

  • decreased neurotransmitter synthesis (blocks pain)

  • decreased opioid receptor density

nociceptor system is functional by when?

15-20 weeks gestation

perceptual dominance

intense pain in one area may increase tolerance in another area

• “masking” another area of pain; dominating

• e.g, severe knee pain may lessen perception of chronic back pain

pain in the older adult also influenced by:

• cognitive, renal, liver function

• alteration of metabolism of drugs and metabolites

• age-associated brain changes

acute pain

• protective mechanism; alerts body of something immediately harmful

• less than 3 months

• clinical manifestations: tachycardia, hypertension, diaphoresis, dilated pupils, anxiety

acute somatic

• pain that arises from joints, muscle, bone, skin

• A-delta fibers: sharp pain, well localized

• C fibers: dull, aching, throbbing pain, poorly localized

acute visceral

• pain that arises from internal organs and linings of the body cavities

• poorly localized; fewer nociceptors

referred pain

• pain that moves away from area of origin to another that is supplied by the same spinal segment

chronic pain

• at least 3 months

• poorly understood

• doesn’t respond to usual therapies

• no protective purpose

• dysregulation of nociceptors and pain modulation processes

• behavioural or psychological change

neuroplasticity

maintains perception/experience of pain

types of chronic pain

• specific or nonspecific spinal pain

• myofacial pain syndrome (MPS)

• post-operative pain

• cancer pain

• central post-stroke pain

• phantom limb pain

• complex regional pain syndrome (CRPS)

neuropathic pain

• dysfunction or primary lesion of the nervous system

• most often chronic

• can cause hyperalgesia and allodynia

• burning, shooting, shocklike, tingling

hyperalgesia

unusually more severe pain than it should be

allodynia

pain from stimulus that doesnt provoke pain

peripheral neuropathic pain

injured nerves become excitable

central neuropathic pain

lesion or neuroplastic changes to brain or spinal cord

neuroanatomy of pain

sensation - afferent pathways

• 1st order neurons (nociceptors) - PNS to spinal gate of dorsal horn

• 2nd order neurons - immediate fibers; “dessucate” to thalamus via spinothalamic tract

• 3rd order neurons - to higher orders of brain

perception - interpretive centers

• brainstem, midbrain, diencephalon, cerebral cortex

response - efferent pathways

• CNS to dorsal horn of spinal cord

A-delta fibers

• myelinated

• transmit sharp, well-localized, fast pain sensations

C fibers

• unmyelinated

• stimulated by mechanical, thermal, and chemical receptors

• transmit dull, aching, burning pain sensations

• slow, poorly localized, longer lasting

A-beta fibers

• LARGE, myelinated

• transmit touch and vibration sensations

phases of nociception

1. transduction

2. transmission

3. perception

4. modulation

• multiple targets for pharmacological intervention

• NSAIDs act on the peripheral level

• opioids act on the CNS

transduction

tissue damage caused by mechanical, thermal, or chemical noxious stimuli that is converted to electrophysiological activity

transmission

pain impulses conduct through A-delta and C fibers to dorsal horn then higher orders of the brain

• afferent pathways

perception

conscious awareness of pain

• sensory-discrimination, affective-motivational, cognitive-evaluative systems

modulation

process of increasing or decreasing transmission of pain impulses throughout the nervous system

• descending tracts of spinal cord

what class of drugs act on the peripheral level

NSAIDS

what class of drugs act on the CNS

opioids

adjuvant analgesics

drugs that affect or mimic the inhibitory neurotransmitters

what are the pathways of modulation

• segmental inhibition

• conditioned pain modulation

• expectancy-related cortical activation

segmental inhibition/Gate Control Theory

• A-alpha and A-beta fibers (nonnociceptive) synapse with the dorsal horn with the A-delta and C fibers (nociceptive)

• travel faster because of larger size and myelination

• results in a decrease of pain

• nociceptive fibers = opens gate = increase pain

• nonnociceptive fibers = closes gate = alleviates pain

conditioned pain modulation

• when two noxious stimuli occur at the same time (pain inhibiting pain)

• basis of pain relief in acupuncture, deep massage, and intense heat or cold

expectancy related cortical activation

• cognitive expectations can exert control over analgesic systems to intensify or inhibit pain

• placebo effect - positive expectations

• nocebo effect - adverse expectations

inhibitory neurotransmitters

GABA and glycine

endogenous opioids

• enkephalins

• endorphins

• dynorphins

• endomorphins

• nociceptin/orphanin FQ

(endocannabinoid - neurotransmitter)

WHO analgesic ladder for baseline treatment

• mild to moderate pain (<4) = non-opioid analgesic

• moderate pain (4-6) = oral opioids

• severe pain (7-10) = parenteral opioids

adjuvant analgesics are added when chronic pain has neuropathic qualities

where do opioids extracted from the poppy plant exert their effects

mu and kappa receptors

true or false: perception and emotional response to pain is altered by opioids; opioids neither lower the threshold nor slow or block the transmission of the pain impulse

true

opioid effects other than analgesia:

• suppresses cough reflex

• slows GI motility

• respiratory depression

• euphoria and relaxation

• sedation

• nausea and vomiting

can cause physical and psychological dependence!!

how does acetaminophen reduce fever

acts on CNS (hypothalamus stopping prostaglandin synthesis)

adverse effects of acetaminophen

inhibits warfarin (Coumadin) metabolism, causing warfarin to accumulate to toxic levels.

high dose or long term usage may result in elevated warfarin levels and bleeding.

acute toxicity includes nausea, vomiting, chills, and abdominal discomfort. can cause liver toxicity and liver damage