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Epicritic
Pain is easily discernible and well localized
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Protopathic
Pain is not definitely localized & can only be described in a general way
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What are the four subclasses of chronic pain
- Neuropathic
- Mixed
- Nociceptive
- Viscera
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What is the difference between chronic and acute pain
Chronic extends beyond the healing period, and has inadequate explanation for the presence and extent of the pain
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What is the role of A delta fibers in pain
They are thin myelinated fibers that carry localized intense pain that is felt first (fast)
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What is the role of C fibers in pain
They are small unmyelinated fibers that are slow, throbbing and long lasting
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What lamina does pain go through on the way to the brain
- First order neuron: Lamina 2 (Substantia gelatinosa)
- Second order neuron: Lamina 5 (Nucleus proprius)
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What is the role of Periaqueductal Grey (PAG) in pain
They are usually inhibitory to Nucleus Raphe Magnus (NRM), but when activated they no longer inhibit, and the pain is reduced do to the NRM activation
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What does Nucleus Raphe Magnus system excite to reduce pain sensations
Enkephalinergic interneurons in the spinal cord reducing the activity in afferent pain fibers
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How does Lidocaine work
It is a nerve block
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What are the endogenous opiates
- Enkephalin
- - Endorphins
- - Dynorphins
- Opioids
- Endomorphins
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What is lost in a unilateral lesion of the spinothalamic tract
Contralateral loss of pain and temp sensation, symptoms appear 1-2 levels below the lesion
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What will result from a dorsal root lesion
Ipsilateral loss of pain and temperature limited to the dermatomal levels of the lesioned roots
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What causes referred pain
Neurons that are both nociceptive and and non-nociceptive are in lamina V and due to proximity, the brain gets the message wrong
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What is NMDA
An amino acid derivative that acts as a specific agonist at the NMDA receptor mimicking the action of glutamate
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Wind up Theory
Repeated activation of NMDA receptors causes increased response to the same stimulus, like kindling in seizures. Nerve damage can cause this effect.
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Allodynia
Stimuli that is usually non-painful becomes painful
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Hyperalgesia
General perception of painful stimuli becomes more intense
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TCA (anitdepressants) drugs have what contraindiction
They should not be taken by those over 60 years old
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What are some effective local anesthetics
- Capsaicin (lasts weeks)
- Lidocaine (patch available)
- Both can be used topically
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Which Anticonvulsant is preferred Gabapentine or Pregabalin and why
Pregabalin requires a lower dose for the same effect
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TRPV1
Also known as the capsaicin receptor and the vanilloid receptor 1
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What are the contraindictions of the anticonvulsants gabapentine and pregabalin
Dizziness
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What drug has been shown given to patients with herpes zoster can prevent postherpatic neuraglia
Gabapentin
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Low doses of Ketamine during surgery has what effect
It decreases the amount of Opioids needed
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Gabapentin and Pregabalin are anticonvulsants that have what MOA
They block alpha-2-delta subunit calcium channels
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Ketamine and Dextromethorphan are used for what
To help reduce the dose of Opioids needed
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What are the side affects of Opioids
- Sedation
- Confusion
- Respiratory distress
- Pruritis (severe itching)
- Nausea and vomiting
- Constipation
- Miosis
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For what conditions can Opioid therapy be used
- Acute pain
- Cancer Pain
- AIDS pain
- Pain in advanced illnesses
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Opioids fall under a schedule II rating of controlled substances which means
It has a high abuse potential with severe psychic or physical dependence
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Naloxone
This is an Opioid antagonist
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Mu receptors
A class of Opioid receptors
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Endorphin neurotransmitters use what type of receptors
Mu receptors
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Enkephalin neurotransmitters use what type of receptors
Delta receptors
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How do Opioids work on ascending fibers
- They close voltage gated Ca2+ ions on the presynaptic neurons and block neurotransmitter release
- They also hyperpolarize and inhibit postsynaptic neurons by opening K+ channels
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How do Opioids affect descending fibers
They inhibit GABA's actions, GAbA normally inhibit neurotransmitters that prevent pain in the dorsal horn thus increasing the inhibition of pain
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Codeine and Acetaminophen together is equal to
600mg of Ibuprofen
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Why is Fentanyl a popular choice for surgery, and what other uses does it have
- It works fast & doesn't stay in the the system long
- Nasal spray is used for break through pain
- 80-500x more potent then morphine
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What is considered the Gold standard Opioid
Morphine
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Why is Morphine not taken by pregnant women
It reaches the fetus and can cause the baby to be dependent on Morphine
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What are some of the side effects of Morphine
- Depression of Respiration
- Euphoria
- Drowsiness
- Mental clouding
- Nausea and vomiting
- Constipation
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Why is pupillary constriction (Miosis) an important marker with a patient on Morphine
When extreme, it can be a sign that the dosage is too high for the patient
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Meperidine
Part of the strong agonist class of drugs and has a tenth the potency of Morphine, it should not be used for more then 48 hours
Serotonin should not be taken with it because it raises Serotonin levels
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Methadone
- Strong agonist that has a long half life
- This is often used when there are limits to the use of morphine
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Oxycodone (Percodon & Oxycotin)
- In the strong agonist group
- Percodon is the short acting form
- Oxytocin is the long acting form
- Morphine substitute
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Hydrocodone
- Moderate/Weak agonist
- Used for moderate pain
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Vicodin
Combination of Hydrocodon and Acetominophen
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Tapentadol
- New mu-opioid strong agonist
- Can substitute for morphine or oxycodone
- Anti-inflammation effects
- Less side affects
- Less abuse likely
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Buprenorphine
- Partial agonist
- More potent then morphine (binds strongly)
- Less likely to be abused
- Less risk of respiratory depression
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Tramadol
- Weak agonist
- Same side effect issues as other Opioids
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Pentazocine
- Mixed agonist
- Used for mild to moderate pain
- Little respiratory depression
- Little physical dependance
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Buprenorphine, tramadol or pentazocine can by used for what condition
Can help with withdrawal in physically dependent Opioid patient or addicts
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Naltrexone
- Opioid antagonist
- Orally given and has a long duration of action
- Used in drug addiction treatments
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