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Nervous System II > Pain Management > Flashcards

Pain Management Flashcards

1
Q

Enkephalins

A

Endogenous pentapeptides derived from pro-enkephalin

Two families: (Met) enkephalin and (Leu) enkephalin

Rapidly broken down by peptidases, so act only at a short distance (synapse)

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2
Q

Endorphins

A

Derived from proopiomelanocortin (POMC)

B-endorphin - 31 amino acid peptide; less susceptibility to degradation by proteases allows it to act more systemically as both a neuropeptide and a neurohormone

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3
Q

Dynorphins

A

Derived from prodynorphin

Dynorphin A is K-opioid receptor selective

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4
Q

Where do opioid receptors function in the brain?

A 
PAG (descending pain)
Medulla nuclei (respiratory depression) 
Spinal cord dorsal horn (ascending pain) 
Limbic regions (affective response to pain) 
Reinforcement regions (addiction/abuse)
Gut (constipation)
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5
Q

Indications for clinical use of opiates

A

Relief of moderate to severe pain associated with:

Malignancy
Post-operative pain
Obstetrical anesthesia
Patient-controlled analgesia
Alleviation of pain and myocardial load in MI
Alleviation of dyspnea associated with cardiac dysfunction

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6
Q

What is the mechanism of respiratory depression in opiate use?

A

Decreased sensitivity to CO2 levels in brain stem respiratory centers

Increased blood CO2 levels leads to cerebral vasodilation, which can exacerbate head injury via elevation of ICP

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7
Q

Contraindications to opioid use

A 
Compromised respiratory function (asthma, emphysema, severe obesity) 
Suspected head injury 
Hypotension / Shock 
Histamine release
Hypothyroidism 
Impaired hepatic function
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8
Q

Use of opiates in cough

A

Provide symptomatic relief from cough at lower doses than necessary for analgesia and respiratory depression

Codeine
Dextromethorphan - non analgesic opiate

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9
Q

Which opiate use effects do not demonstrate tolerance?

A

Pupillary Constriction (Miosis)

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10
Q

Use of opiates in GI

A

Anti-diarrheal / induction of constipation following GI surgery

Loperimide (Imodium) and diphenoxylate act locally in GI tract and are not absorbed into bloodstream; Schedule IV (low abuse potential)

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11
Q

Histamine-mediated side effects of opiates

A

Itching
Urticaria (hives)
Local vasodilation
Headache

Exacerbation of asthma symptoms
Peripheral vasodilation with decreased blood pressure

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12
Q

Cardiovascular effects of opioid drugs

A

Decreased cardiac work load
Orthostatic hypotension via inhibition of baroreceptor reflex

Therapeutic uses: MI (analgesia and decreased cardiac load)

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13
Q

Therapeutic use of opioids in pulmonary edema

A

Useful in pulmonary edema associated with cardiac dysfunction

Alleviation of dyspnea

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14
Q

Opioids - DDIs

A

Barbituates - synergistic CNS depression

Antipsychotics - synergistic respiratory depression

MAOI Inhibitors and TCADs - increased respiratory depression; risk of CNS excitation, delirium, seizures

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15
Q

Opioids - Pharmacokinetics

A

Absorption: Oral, but efficacy is increased if given parenterally due to first-pass hepatic metabolism

Rapidity of onset (and abuse potential) is highly correlated with lipid solubility

Metabolism: morphine is conjugated with glucuronide in the liver; morphine-6-glucuronide is a potent metabolite

Excretion via urine

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16
Q

Tramadol - Mechanism

A

Acts at mu receptors but also blocks monoamine reuptake; potentiates descending analgesic pathway

17
Q

Demerol

A

Used to treat severe, short term pain

Faster onset/offset than morphine with decreased biliary spasm, constipation, tolerance

Not antitussive

Toxic metabolites cause CNS excitation; limits use to short-term

18
Q

Buprenorphine - Mechanism

A

Partial mu agonist; can cause analgesia but precipitates withdrawal in opiate dependent patients

19
Q

Pentazocine & Butorphanol

A

K agonist, mu antagonist

Used for spinal analgesia with less respiratory depression

Precipitates withdrawal in patients dependent on mu agonists

20
Q

Naloxone vs. Naltrexone

A

Competitive antagonists of mu receptors

Naloxone is short acting and not orally active; Naltrexone is longer acting and orally active

21
Q

Codeine metabolism

A

Codeine is an agonist at mu opioid receptors; additionally, 10% of the dose is metabolized to morphine by CYP2D6

10% of Caucasians are deficient in this enzymatic pathway and may experience diminished analgesia with codeine

22
Q

Delta opioid receptors

A

Endogenous agonists - Met/Leu enkephalins, B-endorphins; produce analgesia without respiratory depression

No exogenous agonists available

23
Q

Kappa opioid receptors

A

Endogenous agonists - Dynorphins

Exogenous agonists - Pentazocine

Produce spinal analgesia with reduced respiratory depression

24
Q

Opioid withdrawal

A

Characterized by:

Dilated pupils
Insomnia / restlessness
Rhinorrhea
Sweating
Diarrhea
Nausea
Cramps
Chills

Clonidine (a2-adrenergic agonist) treats withdrawal symptoms

25
Q

Neuropathic Pain

A

Pain that persists and has become disengaged from noxious stimuli or the healing process; often a result of nervous system damage or pathology

Often presents with paresthesias, hyperalgesia, allodnia; ex: postherpetic neuralgia, diabetic neuropathy

26
Q

Nociceptive Pain

A

“Normal” pain resulting from active of nociceptive nerve fibers; may be somatic or visceral

27
Q

Acute Pain Management Guidelines

A

Mild Pain (1-3): NSAID +/- adjuvant

Moderate Pain (4-6): slow titration of short acting opioids + NSAID +/- adjuvant

Severe Pain (7-10): rapid titration of short acting opioid + NSAID +/- adjuvants

28
Q

How do NSAIDs affect post-op opioid requirements?

A

Reduction by 20-40%

29
Q

Acetaminophen

A

Inhibits COX-2 in the CNS to block central sensitization only; no peripheral anti-inflammatory action

Major dose-limiting side effect is hepatotoxicity; daily dose should not exceed 3.25-4g/day

30
Q

Multimodal pain management - drug classes

A 
Opioids
NSAIDs / Acetaminophen 
Local anesthetics 
a-2 adrenergic agonists (Clonidine) 
NMDA receptor antagonists (Ketamine)
31
Q

Role of a-2 adrenergic agonists in pain management

A

i.e. Clonidine

Act on post-synaptic receptors on dorsal horn neurons to decrease ascending pain transmission

May decrease opioid requirements; administered via epidural infusion in cases of severe, intractable pain as adjunct to neuraxial opioids

Side effects: Hypotension, bradycardia, sedation, rebound hypertension

32
Q

Role of NMDA receptor antagonists in pain management

A

i.e. Ketamine

Blocks glutamate binding at NMDA receptors in ascending pain pathway; reduces development of tolerance to long-term opioid use

Nervous System II (12 decks)

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