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21 Cards in this Set
- Front
- Back
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Compare procaine to tetracaine
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substitution of butyl group for amine group on benzene ring results in tetracaine
tetracaine more lipid soluble more lipid soluble ten times more potent longer duration of action 4-5 fold decrease in rate of metabolism |
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compare mepivicaine to bupivicaine
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bupivicaine is 35 more times more lipid soluble
potency and duration 3-4 times that of mepivacaine |
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Frequency dependent blockade
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a resting nerve is less sensitive to local anesthetic-induced conduction blockade than is a nerve that has been repetivley stimulated
EX: etidocaine blocks motor nerves before sensory nerves because of frequency-dependent blockade |
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Cm
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the minimum concentration of local anesthetic necessary to produce conduction blockade of nerve impulses
larger nerve fibers require higher concentrations of local anesthetics for production of blockade (analogus to MAC of inhalationals) |
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cm with motor and sensory
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Cm of motor fibers is twice that of sensory
(may not have have skeletal muscle paralysis with sensory blockade) |
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what do you need for conduction blockade
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A fiber: expose at least two and preferably three successive nodes of Ranvier (1 cm) to adequae concentration of local
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why use epinephrine with locals
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duration of local anesthetic is proportional to the time the drug is in contact with nerve fibers, so epi is added to produce vasoconstriction which limits systemic absorption and maintains concentration in the vicinity of the nerve fibers
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transient neurologic symptoms of locals
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moderate to severe pain in the lower back, buttocks and posterior thighs that appear within 6-36 hours after complete recovery from eventful spinal
no etiology full recovery in 1-7 days |
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what could increase lumbosacral nerve irritation
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exaggerated when the nerves are stretched by placement of the patient in the lithotomy position
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what happens with cauda equina syndrome
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diffuse nerve in jury across the lumbosacral plexus producing:
-sensory anesthesia -bowel and bladder sphincter dysfunction -paraplegia |
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what is anterior spinal syndrome
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lower exremity paresis with a variable snesory deficit that is usually diagnosed as neural blockade resolves
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dose dependent effects of lidocaine in mcg/ml
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1-5: analgesia
5-10: circumoral numbness tinnitus skeletal muscle twitching systemic hypotension myocardial depression 10-15: unconsciousness apnea coma 15-25: apnea coma >25: cardiovascular depression |
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how do local effect the heart
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low doses: cardiac antidysrhythmic
high doses: conduction and automatcity blocked |
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methemoglobinemia
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decreased oxygen carrying capacity
causes oxidation of hemoglobin to methemoglobin cannot bind to O2 or CO2 resulting in loss of the hemogloin molecules transport function central cyanosis when metHgb exceeds 15% probable when there is difference between calculated and measured arterial saturation confirmed with qualitative measurement of metHgb reversed with methylene blue 1-2 mg/kg IV over 5 minutes (total dose not to exceed 7-8 mg/kg levels normal in 20-60 minutes therapeutic levels short b/c methylene cleared before all metHgb converted to Hgb |
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six sites of placement of local anesthetic solution
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topical or surface anesthesia
local infiltration peripheral nerve block IV regional anesthesia epidural anesthesia spinal anesthesia |
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what affects onset of emla cream
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skin blood flow
epidermal and dermal thickness duration of application presence of skin pathology |
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how are peripheral nerve blocks taken up
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local anesthetic solutions diffuse from outer surface (mantle) toward the center (core) of nerve along a concentration gradient
so nerve fibers located in the mantle of the mixed nerve are anesthetized first |
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contrast epidural to spinal
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no zone of differential sympathetic blockade
zone of differential motor may be up to four segments below sensory larger doses required to produce epidural anesthesia |
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what do dosages of spinals vary according to
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height of pt which determines volume of subarachnoid space
segmental level of anesthesia desired duration of anesthesia desired |
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risk factors for hypotension with spinal
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sensory anesthesia above T5
baseline systolic BP <120 |
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risk factors for bradycardia with spinal
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sensory anesthesia above T5
baseline heart rate <60 BPM prolonged PR interval beta blockers |
