Pain Flashcards
What is Nociception? (pain process)
Transduction
Transmission
Perception
Modulation
Types of noxious stimuli
Mechanical: incision, tumor mass
Thermal: burn, frostbite
Chemical: toxin, chemotherapy
Transduction
conversion of a mechanical, thermal, or chemical stimulus to a neuronal action potential
Starts in the periphery in response to noxious stimuli; where primary nociceptive fibers (afferents) are activated
Which causes the nociceptors cause the release of serotonin, bradykinin, histamine, substance P, and prostaglandins
Opioid receptor sites can be found in the CNS, peripheral nerves, and GI tract
Naturally occurring morphine-like substances :
Endorphins
Enkephalins
Transmission
Second step of nociception
Where the stimuli move from the peripheral nervous system, to the spinal cord through the dorsal root ganglion, into the ascending tract to the brain
Types of Nociceptive fibers:
A – delta (δ) fibers:
Thinly myelinated, large in diameter, and fast-conducting fibers
Transmit sharp, localized (somatosensory) pain that is sensitive to mechanical and thermal stimuli
C-fibers:
Unmyelinated, small in diameter, and slow-conducting fibers
Transmit dull, aching (visceral) pain that is diffuse
Mu (μ): Primarily pain receptors (most common)
Analgesia, respiratory depression, euphoria,
decreased GI activity, sedation, and physical dependence
Kappa (k):
Some analgesia, sedation, decreased GI motility
Dysphoria
Somatic Pain
Well-localized
Sharp, aching, throbbing, gnawing
Activation of nociceptors resulting from cutaneous, musculoskeletal, and deep tissues
Examples: Bone pain, soft tissue injury
Visceral
Poorly localized
Deep, aching, cramping, pressure, referred
Activation of nociceptors resulting from stretching, distention, or inflammation
Examples: bowel obstruction, biliary colic
Full Opioid Agonists
Bind to opioid receptors resulting in activation
Activation of mu receptors leads to analgesia (pain reliever) as well as respiratory depression, euphoria, and sedation
Activation of the kappa receptors leads to analgesia as well as sedation and decreased GI motility
Medications:
Morphine, Fentanyl, Codeine, Oxycodone, Hydromorphone, Meperidine, and methadone
Common side effects: respiratory depression, constipation, orthostatic hypotension, and urinary retention
High risk of dependence; are controlled substances
Morphine
Is the GOLD standard
Affect central and peripheral receptors
Not the drug for everyone (can be allergic)
Major side effects: analgesia, drowsiness, mental clouding, respiratory depression, constipation, urinary retention, nausea and vomiting, hypotension, pruritis
Has active metabolites, such as M6-G, which can accumulate
Multiple routes of administration and formulations
Hydromorphone (Dilaudid)
Pharmacologic effects essentially identical to Morphine
Often confused with morphine (stronger than Morphine)
Most potent than Morphine, but not more effective
No active metabolites
Both drugs are available in short-acting forms
No extended-release form hydromorphone – available
Oxymorphone extended-release available in 4 dose sizes
Food and drink can affect absorption of extended-release formulation
Hydromorphone (Dilaudid)
Pharmacologic effects essentially identical to Morphine
Often confused with morphine (stronger than Morphine)
Most potent than Morphine, but not more effective
No active metabolites
Both drugs are available in short-acting forms
No extended-release form hydromorphone – available
Oxymorphone extended-release available in 4 dose sizes
Food and drink can affect absorption of extended-release formulation
Codeine, Hydrocodone, and Oxycodone (take for mild pain)
Codeine
About 10% is metabolized to morphine by CYP 2D6 pathway
About 10% of Caucasians are poor metabolizers
25% Ethiopians are rapid metabolizers
Constipation a major side effect
Effectiveness basically the same of ASA or acetaminophen
Hydrocodone
Has a better side effect profile than Codeine
Not available as a single entity
Oxycodone
Available in short-acting (tablets and liquid) and extended-release formulations
Meperidine (Demerol)
Proven to be not as effective as originally thought
Rapid onset but with short duration of action
Active metabolites- 2-4 hours
No evidence that efficacy enhanced by Vistaril or Phenergan
Does not have a lesser effect on the sphincter of Oddi
300 mg PO = 10 mg of IV morphine
Now limited to use in short procedures or to treat rigors
NOT used for long term
Tramadol (Ultram)
-Weak mu opioid agonist
-Blocks reuptake of norepinephrine and serotonin
Is not a controlled substance
Analgesic ceiling
Has active metabolites
Side effects: nausea, dizziness, confusion, seizures, dry mouth
