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nocioception
process of transduction, transmission, perception, and modulation of pain
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T or F, nocioception varies widely among individuals?
F, similar
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T or F, pain experience and response is similar among individuals?
F, varies widely
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pain threshold
point where a stimulus is perceived as painful
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pain tolerance
max intensity of pain that an individual can endure before they want action taken
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how do pain threshold and pain tolerance vary among individuals?
- threshold is fairly uniform
- tolerance varies widely
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2 major classifications of pain
nocioceptive and neuropathic
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2 types of nocioceptive pain
somatic or visceral
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nocioceptive pain
results from ongoing stim of nerves from a noxious stim
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somatic pain
- type of nocioceptive pain
- identifiable focal point
- follows nerve distribution
- well localized, sharp, pain at point of stimulus
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visceral pain
- type of nocioceptive pain
- diffuse and can be referred to another area
- dull and vague
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What type of pain med does nocioceptive pain respond best to?
NSAIDs and opioids
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neuropathic pain
- caused by abnormal processing of painful stimuli
- CNS dysfunction allows for spontaneous excitation leading to severe pain
- peripheral or central generation
- difficult to treat
- described as burning, tingling, or shock like
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T or F, neuropathic pain may be associated with subjective numbness, loss of sensation, or weakness
T
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What type of pain med is effective in treating neuropathic pain?
- Adjunctive meds
- NSAIDs and opioids are not very effective
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Adjunctive analgesic
- med used primarily for other reasons than analgesia
- ex: TCA, anti-convulsant meds
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acute pain
- mostly nocioceptive
- peripheral nocioceptive response is activated by noxious stimuli
- associated with neuro endocrine stress response proportional to level of stimulus
- resolves within a few days to weeks
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chronic pain
- lasts longer than course of disease or injury (1-6 months post healing)
- nocioceptive or neuropathic
- psych or enviro factors play a major role
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What nerve fibers carry pain sensation?
- A delta and C fibers
- sensory (afferent)
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Describe the pain that A-delta fibers carry
- fast pain, AKA 1st pain
- fibers are myelinated
- sharp prickling pain that is acutely localized
- duration coincides with duration of the stimulus
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Describe the pain that C fibers carry
- slow pain, AKA 2nd pain
- unmyelinated
- burning and diffuse pain
- pain may exceed the duration of the stimulus
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Acute pain is ___ (fast or slow?) pain and is carried by ___ fibers
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Chronic pain is ___ (fast or slow?) pain and is carried by ___ fibers
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Deafferentiation pain
- chronic pain associated with a loss of sensory input
- ex: amputation
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T or F, chronic pain is complex and involves changes in the nervous system both centrally and peripherally?
T
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Neospinothalamic tract
- fast A-delta fibers travel via this pathway
- synapse at lamina 1 and 5
- pain travels to midbrain (thalamus)
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Main afferent (sensory) pathway of the spinal cord
spinothalamic
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paleospinothalamic
carries slow (C fiber) pain transmission to reticular formation in the brain stem
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What are the 2 divisions of the spinothalamic tract?
neospinothalamic and paleospinothalamic
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Where do afferent C fibers synapse in the spinal cord?
lamina 2 and 3
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substantia gelatinosa
- AKA lamina 2
- afferent C fibers synapse here in the spinal cord
- plays a major role in processing and modulating nocioceptive input
- major site of action of opioids
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What part of the spinal cord receives all the afferent neuron activity?
dorsal horn
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dorsal horn
principle site of modulation of pain by both ascending and descending neuro pathways
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pain pathway is the _____ tract
spinothalamic
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T or F, pain sensations cross the spinal cord?
T
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Describe the path of pain sensations traveling in either A-delta or C nerve fibers
- synapse in the dorsal horn of the SC
- ascend 1-3 segments in the tract of lissauer
- synapse with a 2nd order neuron
- crosses midline
- ascends via contralateral spinothalamic tract to the brainstem
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What are the 2 types of 2nd order neurons?
- nocioceptive- serve only noxious stimuli
- wide dynamic range neurons- carry noxious and non-noxious stimuli
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What type of neurons are capable of wind up
wide dynamic range neurons
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What is "wind up"
- with repeat stimulation, wide dynamic range neurons increase their firing rate in a graded fashion
- preemptive analgesia is thought to prevent this
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periaqueductal grey
- grey matter in the mid brain
- when there is afferent stimulation of the periaqueductal grey the efferent (downward) pathway is activated
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How is the periaqueductal grey area stimulated?
when there is afferent stimulation of the periaqueductal grey the efferent (downward) pathway is activated
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Major NT released from C fibers
substance P
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T or F, release of substance P activates the arachidonic pathway?
T
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How does the substantia gelatinosa modulate pain?
- c fibers synapse with inter neurons in the SG
- this causes substance P to be released
- SG releases enkephalins which decreases the release of substance P
- this decreases the number of action potentials in the interneuron pain pathway and ultimately the pain perception is decreased
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Major NT released from A delta fibers
glutamate, an excitatory NT
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substance P works via what receptor
NK-1
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glutamate works via what receptor
NMDA
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What are examples of alpha 2 adrenergic agonists?
clonidine and precedex
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activation of the alpha 2 receptor leads to...
where are the receptors located?
- pain inhibition
- dorsal horn of the spinal cord
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ketamine MOA
NMDA antagonist
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What are the old names for opioid receptor 1?
2?
3?
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supra spinal analgesia is mediated primarily by ____
mu 1, although mediated by all opioid receptors
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spinal analgesia is mediated primarily by ____
mu 2, although mediated by all opioid receptors
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what opioid is unique in that it is a potent mu receptor agonist but has minimal kappa and delta activity?
remi
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properties of mu 1 receptor activation
decreased HR, euphoria, low abuse potential, urine retention
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properties of mu 2 receptor activation
resp depression and physical dependence
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properties of delta receptor activation
resp depression and physical dependence
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properties of kappa receptor activation
dysphoria, sedation, low abuse potential
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T or F, opioids stimulate different receptors than the body's endorphins and enkephalins?
F, opioids stimulate the same receptors
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how does spinal analgesia work?
- opioid is injected into the spinal or epidural space
- it diffuses into the substantia gelatinosa (lamina 2)
- unites with opioid receptors in the nerve terminal
- release of substance P is reduced and
- transmission of nerve impulses thru the substantial gelatinosa is inhibited
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IV opioids affect what area of the brain
periaqueductal grey in the midbrain
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what is primary hyperalgesia
- increased pain sensitivity
- mediated by release of substances from damaged tissues
- type of peripheral pain modulation
- prostaglandins are released after tissue damage, phospholipids form, arachidonic cascade is set off
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what is secondary hyperalgesia
- increased pain sensitivity
- type of peripheral pain modulation
- neurogenic inflammation
- mediated by substance P
- allogens? are released from the damaged tissue (bradykinin, 5HT3) and can irritate nerve endings leading to pain
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is wind up an example of central or peripheral pain modulation?
central
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3 types of central modulation
- wind up
- receptor field expansion
- hyper excitability of flexion reflexes
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what is receptor field expansion?
- a type of central pain modulation
- dorsal horn neurons increase their receptor fields such that adjacent neurons become responsive to stimuli to which they were previously unresponsive
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what are the 2 pathways of arachidonic acid breakdown?
- cyclooxygenase to prostaglandins to bradykinin and O2 free radicals leading to inflammation and pain
- lipoxygenase to leukotrienes to inflammation
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allogen
- pain producing substance
- all end products of arachidonic acid breakdown are allogens
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what are examples of meds that interrupt the arachidonic acid breakdown pathway?
corticosteroids, NSAIDs, tylenol, ASA
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what systemic effects can tissue injury have?
- anxiety and demoralization
- DVT (decr flow and Plt aggregation)
- muscle splinting
- PNA (immobile)
- coronary ischemia (increased O2 consumption)
- poor wound healing (increased cortisol and hyperglycemia)
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T or F, activation of the RAAS and immunosuppression may result from tissue damage and pain
T
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what are risk factors for reap depression with PCA use?
- OSA
- older age
- basal infusion
- hypovolemia
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most common SE of opioid PCA
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risk of using demerol in an elderly or renal failure pt
accumulation of normeperidine leading to seizures, anxiety, tremors, myoclonus
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why might clonidine be added to an epidural
- alpha 2 agonist
- reduces sympathetic outflow from the brain stem; inhibit 2nd order neurons in the dorsal horn of the spinal cord
- sedation is dose related
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dose of nalaxone recommended for respiratory depression but to avoid reversal of analgesia
0.04 mg increments
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epidural onset time is directly proportional to
lipid solubility
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fent is highly ____ ____ and thus has a ___ onset
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fent can cause (early or late) resp depression
early (fast onset and short DOA)
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morphine is ___ and thus has a ___ onset
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which has more rostral spread- morphine or fentanyl? why
morphine, it's water soluble and thus diffuses out of the CSF slowly and thus can travel up toward the brain
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morphine can cause (early or late) resp depression
late
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Patho r/t complex regional pain syndromes
SNS dysfunction
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T or F, neuropathic pain is easily treated with opioids
F
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T or F, a different opioid at an equianalgesic dose may be effective in treating chronic pain
T
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how do TCA work to decrease neuropathic pain?
block NMDA mediated activity
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how do SSRIs work to decrease neuropathic pain?
- block reuptake of serotonin and NE
- serotonin is an important INHIBITORY NT in the pain pathway
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how do anti-convulsants help with chronic pain?
- alter ion channels along the nerve fiber and block the action potential and thus the painful stimuli
- helpful for neuropathic pain
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reasonable treatment goals for LT pain management
- reduction of pain intensity
- increased physical functioning
- proper medication use
- improvement of sleep, mood, and interactions with others
- return to work for normal daily activities
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