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Describe the basic aspects of the pain pathway.
- Transduction- conversion of noxious stimuli into electrical signal via nociceptors (thermal, mechanical, chemical)
- Transmission- A-delta fibers (fast, localized pain), A-beta fibers (poorly reactive, light touch), C fibers (poorly localized, dull, delayed pain)
- Modulation- signal travels up spinal cord dorsal horn, incoming signals are summated and altered
- Projection- signal travels to brainstem
- Perception- integration, processing of pain, behavioral or motor responses
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What pain management tools alter perception? (7)
- opioids
- tramadol
- alpha-2 agonists
- ketamine
- tricyclic antidepressants
- NSAIDs
- benzos
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What pain management tools alter modulation of pain? (5)
- opioids
- alpha-2 agonists
- local anesthetics
- ketamine
- NSAIDs
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What pain management tools prevent transmission of pain signals? (1)
local anesthetics
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What pain management tools prevent transduction from local nociceptors? (3)
- NSAIDs
- local anesthetics
- opioids
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Describe A-delta, A-beta, and C fibers.
- A-delta: low threshold (pressure, vibration), mechanoreceptors, fast, myelinated
- A-beta: high and low threshold (pressure, pain), mechanoreceptors and nociceptors, fast, myelinated
- C: high threshold mechanoreceptors, thermoreceptors, nociceptors, slow, unmyelinated
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Describe peripheral nerve terminal sensitization.
inflammatory soup converts high threshold receptors to low threshold receptors (more sensitive), activated silent ("sleeping") receptors--> more input to nociceptors
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What is central sensitization?
- persistent nociceptive input after peripheral sensitization causes signal recruitment and amplification locally and at the level of the spinal cord
- repetitive firing of excitatory neurons
- minor, non-painful stimuli result in excessive pain sensation
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Describe pre-emptive analgesia.
goal is to prevent amplification (sensitization) from occurring, resulting in decrease post-op pain and decreased anesthetic requirements (reduced MAC)
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Describe multi-modal analgesia.
aim to impact the amplification response in as many places as possible to decrease pain
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__(2)__ are more sensitive physiologic indicators of pain than __(2)__.
- resp rate and character; HR or BP
- [still, better to use behavioral indicators than physiologic]
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Describe emergence delirium and how it is differentiated from pain?
- emergence delirium- dissociative behavior on emergence from anesthesia; looked similar to pain in vocalization, thrashing, altered mentation
- Begin with analgesia (err on the side of pain); if it doesn't resolve with analgesia, titrate opioid antagonist; if still bad, consider sedation
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