Test 3 Flashcards
transition from acute to chronic pain can be initiated or maintained by peripheral and/or central mechanisms
dorsal root ganglion
cord
supratentorial
chronic pain definition
pain that has no biological benefit and lasts longer than 3 months (or the normal healing time)
what is the clinical manifestation of peripheral sensitization?
hyperalgesia
what is peripheral sensitization?
enhanced excitability of nerves
reduced nociceptive thresholds
renders high-threshold nerve endings responsive to normally non-noxious stimuli
some effects of nerve injury
- sprouting of new hyperexcitable nerve endings
- neuroma
- reduced thresholds
pain caused by CHANGES in peripheral or CNS is defined as
neuropathic pain (which leads to hyperalgesia and allodynia)
central sensitization involves __ neurons, which is responsive to __
second order wide dynamic range
responsive to GLUTAMATE (NMDA receptor)
(usually in the dorsal horn)
what’s the difference between acute and chronic pain?
constant dumping of quanta of glutamate and opening of the magnesium plug
how do anticonvulsants help?
inhibit neuron excitation and stabilize membrane
what are the first generation anticonvulsants?
carbamazepine and phenytoin
what are the second gen anticonvulsants?
gabapentin and neurontin
what do anticonvulsants treat?
postherpetic neuralgia, diabetic neuropathy, trigeminal neuralgia, others
what is the mech of action of anticonvulsants?
block alpha 2 delta subunit of PREsynaptic voltage gated calcium channels in CNS
how do antidepressants work?
- block reuptake of serotonin and norepi, which are inhibitory neurotransmitters in the descending inhibitory pathway
- block sodium and ca++ channels
- decrease prostaglandin and TNF
- block NMDA receptors
- enhance opioid receptors
How long does it take for antidepressants to enhance opioid receptors?
4-10 days
what are the three classes of antidepressants?
tricyclics, selective norepi reuptake inhibitors, and selective serotonin reuptake inhibitors
name 2 selective norepi reuptake inhibitors
effexor (venlafaxine) and cymbalta (duloxetine)
Cymbals effect norepi
name 2 selective serotonin reuptake inhibitors
prozac (fluoxetine) and celexa (citalopram)
Prozac is the flux that holds Alexis’ pram together
what are the side effects of tricyclics?
muscarinic (think glyco), histaminergic (think benadryl), and adrenergic (think alpha blocker)
caution: recent MI, prolong QT interval
what might happen if you combine a selective norepi reuptake inhibitor with a selective serotonin reuptake inhibitor or a triptan?
serotonin syndrome (anxiety, agitation, delirium, seizures, hyperthermia, diaphoresis, tachycardia, htn or hypotension, hyperreflexia, myoclonus, muscle rigidity)
how would you treat serotonin syndrome due to concomitant use of SNRI and SSRI
lipid emulsion
how do corticosteroids work?
prevent release of arachidonic acid by inhibiting phospholipase A2 on cell membranes (precursor of prostaglandins)
what nerve fibers are blocked by corticosteroids?
C fibers
the effects of corticosteroids are dependent on the degree of HPA axis suppression
hypothalamic - pituitary - adrenal axis
how long can an epidural steroid injection cause HPA suppression?
4-5 days after injection up to 5 weeks
in the event of major surgery during that time, you should give them a dose of exogenous steroid
how does methadone work?
the S isomer antagonizeS NMDA receptorS and inhibits reuptake of Serotonin and norepi
the R isomer binds to opioid Receptors
side effects of methadone
resp depression, excessive sedation, QT interval
