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167 Cards in this Set
- Front
- Back
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what is the primary concentration gradient in a neuron?
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3 Na out for 2 K in
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what does the concentration gradient favor in neuron?
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*extracellular diffusion of K
*intracellular diffusion of Na |
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what is the cell membrane more permeable to?
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K
*relative excess of - ions accumulate intracellularly |
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what accounts for the - resting membrane potential
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K
*excess accumuluation intracellularly |
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what is the resting membrane potential for neurons?
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-70mv
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what is active transport?
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Na/K/ATPase pump
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what is passive diffusion?
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concentration gradient
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what types of channels do LAs have an affinity for?
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active and inactive Na channels
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what passes through the neuronal sheath more easily?
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lipid soluble drugs
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what are nerve fiber actions dependent on?
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*axonal diameter
*degree of myelination |
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describe the cascade of the motor, sensory & ANS system in regards to LAs in spinal anesthesia?
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ANS > sensory > motor
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the initial response to LAs
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ANS is 2 dermatomes higher
motor block @ T10 sensory block @ T8 ANS block @ T6 |
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what are the relative measures of potency in LAs?
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*type of neuron
*diameter of neuron *sensitivity of neuron |
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what are the types of nerve fibers?
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*A alpha
*A beta *A gamma *A delta *B *C |
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describe the A alpha nerve fibers?
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*12-20micron
*1 sensitivity *proprioception/large motor |
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describe the A beta fibers?
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*5-12 microns
*1 sensitivity *sm motor/touch/pressure |
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describe the A gamma fibers?
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*3-6 microns
*1 sensitivity *muscle tone |
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describe the A delta fibers?
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*2-5 microns
*slower conduction *0.5 sensitivity *temp/sharp pain |
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describe the B fibers?
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*some myelination
*3 microns *0.25 sensitivity *preganglionic/ANS |
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describe the C fibers?
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*0.3-1.2 microns
*0.5 sensitivity *dull pain/temp/touch *blocked quickly *postganglionic/sympathetic |
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where are the C fibers located?
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sympathetic > highly conductive
*dorsal horn > pain/temp/touch |
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what are the properties of LAs?
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*affinity for Na channels
*action is voltage & time dependent *may block Ca/K channels *may block NMDA receptors |
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what is important about blocking Ca channels when using LA?
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*can decrease myocardial contractility
*can decrease NT release from presynaptic terminals |
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What is the sequence of LA?
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*sympathetic block
*loss of pain/temp(cold)/touch *loss of touch and pressure *motor paralysis *loss of proprioception * |
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what are the CV implications w/LAs?
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*all are generally myocardial depressants
*rarely impact CV d/t small amt given *don't usually get systemic effects |
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what are the properties of LAs?
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*onset is r/t pKa
*potency is r/t lipid solubility *DOA is r/t protein binding & lipid solubility |
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what two factors of LAs are determined by lipid solubility?
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*potency
*duration of action |
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what happens w/decreased lipid solubility?
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inc onset of action
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what happens w/alkalinization and LAs?
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*add bicarb 1cc 8.4%/10cc Lido
*speeds onset *improves quality of block *prolongs block (r/t inc amt of free base) *dec pain durin SQ infil |
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what happens w/increased protein binding?
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*inc elimination
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what happens w/molecular size and LAs?
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bigger the molecule, the longer it stays around
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what is the pKa range of LAs?
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8.0 - 9.0
*weak bases |
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if an LA pKa is closer to physiologic pH, what happens?
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*higher concentration of nonionized base
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what happens w/a larger nonionized base of LAs?
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passes through nerve cell membranes
*faster onset of action |
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what is pKa?
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the pH @ which 50% ionized and 50% nonionized
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what is the physiologic norm of pH?
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7.4
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what happens w/a nonionized drug?
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passes BBB/placenta
*has greater effect |
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what are weak acids of LAs?
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Na + drug
Ca + drug Mg + drug |
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what are weak bases of LAs?
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Cl + drug
Sulfate + drug |
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what is more effective @ the receptor site?
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cation form
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where is the primary site of action of LAs?
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intracellular side of Na channels
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what is the predominant form for an active LA?
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charged form
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what does the uncharged form of an LA do?
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important for rapid penetration of cell membranes
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what happens to a LA in an acidic environment?
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ECF cation is decreased
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what is an acidic environment for an LA?
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an infected site
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what is the structure of lipophilic LA?
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*benzene or aromatic ring
*physiochem properties r/t substitutions here |
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what is the structure of ester/amide linkage LA?
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intermediate hydrocarbon chain
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what is the structure of hydrophilic LA?
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tertiary amine
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what kind of charge is a/w a tertiary amine?
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+
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what are some lidocaine properties?
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*gold standard (for comparison)
*neural blockade *antiarrythmic (1 -1.5mg/kg) *blocks SNS effect of intubation (inc HR/BP) *blocks bronchospasms |
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what are important lido properties to consider during intubation?
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*dec CBF
*attenuates inc ICP *block SNS effects (inc HR/BP) *dec hypoxic drive |
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what are lido properties in r/t coagulation?
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*dec coag
*prevention of thrombosis *dec plt aggreg *enhance fibrinolysis |
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what are lido properties in r/t hepatic?
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*dec clearance r/t dec blood flow
*cimetidine & propanolol dec hepatic blood flow *any hepatic insult > dec hep BF --> dec clearance |
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how are LAs prepared commercially?
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*H2O soluble
*pH 6-7 |
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what happens when you add epi to a LA?
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*vasoconstriction
*prolongs block |
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what are the two classifications of LAs?
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*amides
*esters |
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how do you know an LA is an amide?
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I before aine in the name
(ie lidocaine, ropivacaine, etc) |
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What type of classification is lido?
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amide
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Does lido vasoconstrict/dilate?
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vasodilates
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what is the OA/DOA of lido?
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rapid onset
short-moderate DOA |
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what is the max dose of lido?
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3-5 mg/kg
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what is the max dose of lido w/epi?
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5-7mg/kg
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what is the toxic dose of lido?
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6.4mg/kg
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how long does epi prolong the effect of lido?
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50%
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what are the uses of lidocaine?
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*topical
*nerve block *infiltration *spinal *epidural |
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how is lidocaine met?
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rapidly by the liver
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what can lidocaine be used for besides LA?
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ventricular irritability
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what is the pKa of lido?
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7.8
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what classification is bupivicaine?
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amide
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what is the OA/DOA of bupi?
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slow onset (15-20 min)
long DOA (1-2 hrs) |
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what is the max dose of bupi?
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1.6mg/kg
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what is the max dose of bupi w/epi?
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2.5 mg/kg
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what is bupi used for?
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*epidural
*caudal *spinal *infiltration *nerve block |
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describe the protein binding of bupi?
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highly protein bound
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what is the elimination time of bupi?
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*210 min
*r/t protein binding |
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describe the potency of bupi?
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potent
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what are the CV effects of bupi?
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*very cardiotoxic
*protein affinity binds it to protein receptors in ion channels in heart *pt resistant to resuscitative efforts |
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what is the contraindication for its use?
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bier blocks (IV regional)
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can bupi cause allergic rxn?
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yes
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what is the pKa of bupi?
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8.1
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what is the classification of ropivicaine?
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amide
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describe the protein binding of ropi?
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highly protein bound
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compare the systemic toxicity of ropi to bupi?
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less toxic
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what is the elimination half time?
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108 min
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what is the max dose of ropi?
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in a 70kg pt it is 200mg
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what are uses of ropi?
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*useful in labor r/t good separation of sensory/motor
*infiltration *nerve block *spinal *epidural |
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what is ropi an analogue of?
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bupi
*less systemically toxic than bupi r/t dec protein binding |
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what is levo bupi?
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*an amide stereoisomer of bupi
*similar to bupi *less cardiotoxic |
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what is the classification of mepivacaine?
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amide
*prolocaine/carbocaine |
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what is the pKa of mepi?
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7.6
*close to physiologic pH, so large % is nonionized |
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why is mepi rarely used in OB?
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*crosses placenta
*effects fetus *fetal hep enzymes not developed, so unable to metabolize |
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what is the onset of mepi?
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medium
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what are the uses of mepi?
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*nerve blocks
*epidural *infiltration |
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what is the max dose of mepi?
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*7mg/kg to a max of 400mg
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what is the pKa of mepi?
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7.6
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what is mepi used for mostly?
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nerve blocks
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what is the class of procaine?
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ester
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what is the OA/DOA of procaine?
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*slow onset
*short DOA |
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what is procaine used for?
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*infiltration
*nerve block *spinal *epidural |
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why do ester LA particularly inc allergic rxn?
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formation of PABA
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what is the pKa of procaine?
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8.9
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what class if prilocaine?
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amide
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what are the uses of prilocaine?
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dental anesthesia
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what is EMLA?
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1:1 ratio of 5% lido and 5% prilocaine in oil/water emulsi
*eutectic mixture of LA |
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what is the depth of penetration of EMLA?
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3-5mm
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how long should EMLA stay on under an occlusive dressing?
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1 hr for effective analgesia
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what is the DOA of EMLA?
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1-2hrs
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what is the max dose of prilocaine?
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400-600 mg for 70kg pt
*7mg/kg |
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what are the uses of prilocaine?
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*infiltration
*nerve block *IV regional *epidural |
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what is the OA/DOA of prilocaine?
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slow onset
*DOA 60-120 min |
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what is the pKa of prilocaine?
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7.8
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what is the caveat regarding prilocaine?
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exception to the pKa onset rule
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what is a caution in prilocaine?
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methemoglobinemia
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what are the uses for EMLA?
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*IV start
*split thickness skin graft (STSG) *laser removal of port wine stains *lithotripsy *circumcision (EMLA contraindicated < 1yoa) |
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what is the max area for EMLA applicatin in:
kids? adults? |
<10kg 100cm2
2000 cm2 |
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what are the SE of EMLA?
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*skin blanching
*erythema *edema |
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what class is etidocaine?
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amide
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what is the OA/DOA of etidocaine?
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fast onset
long DOA (4-8 hrs) |
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what is the pKa of etidocaine?
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7.7
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what class if chloroprocaine?
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ester
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what is the OA/DOA of chloroprocaine?
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*rapid onset
*short DOA |
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*what are the uses of chloroprocaine?
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*infiltration
*nerve block *epidural *caudal |
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what is a SE of interthecal chlorprocaine?
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neurotoxicity
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what is the toxic dose of chloroprocaine?
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22.8mg/kg
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compared to other LA, rate the toxicity of chloroprocaine?
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lease toxic
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how is chloroprocaine metabolized?
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ester hydrolysis
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what is the pKa of chloroprocaine?
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9.0
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what is chloroprocaine's profile w/the onset rule
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it is an exception to pKa-onset rule
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what is the class of tetracaine?
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ester
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what is the DOA of tetracaine?
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intermediate to long acting
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what are the uses of tetracaine?
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*topical
*spinal |
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*what is the max dose of tetracaine?
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2.5mg/kg
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what is the pKa of tetracaine?
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8.2
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what is the sole determinant of tetracaine termination?
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vascular absorption
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what is the class of cocaine?
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ester
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what is unique about cocaine?
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only LA that is a vasoconstrictor
*used on topically on mucous membranes |
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what are the SE of cocaine?
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*highly addictive
*cardiotoxic chronic/acute use |
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what is the pKa of cocaine?
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8.7
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what is the class of benzocaine?
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ester
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what are the uses for benzocaine?
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topical
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what is the byproduct of benzocaine metabolism?
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methemoglobin
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what is the tx for methemoglobinemia r/t benzocaine use?
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methylene blue 1-2mg/kg
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how is benzocaine usually administered?
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*topical
*lozenges |
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describe the rate of absorption of LAs from least to greatest?
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IV > tracheal > Intercostal > caudal > paracervical > epidural > brachial plexus > sciatic/femoral > SQ
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what determines the rate of absorption in LAs?
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vascularity
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how are ester LAs metabolized? 2 types
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*pseudocholinesterases
*ester hydrolysis |
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describe the ester hydrolysis of LAs?
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ester hydrolysis
*rapid *water soluble metabolites excreted in urn |
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what are the two types of pseudocholinesterases that metabolize LAs?
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*plasma cholinesterase
*butyricholinesterase |
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what other drugs can be metabolized by pseudocholinesterases?
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*remifentanyl
*sux |
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what is PABA?
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*breakdown of ester LA
*responsible for allergic rxn |
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name a pt @ risk for toxic SE when using ester LAs?
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pts w/pseudocholinesterase
r/t slower metabolism of drug |
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what is methemoglobinemia in LA?
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a metabolite of prilocaine
*accumulates after large dose *converts heme to metheme |
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how are amide LAs metabolized?
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N-dealkylation
*hydroxylation by CYP 450 |
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is ester or amide LA metabolism quicker?
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ester
*route of metabolism is agent specific |
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list the LAs w/ rate of metabolism?
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Prilocaine > lido > mepi > ropi > bupi
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describe what happens w/LAs and hepatic fxn?
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any dec in hepatic fxn/flow will dec metabolic rate and inc risk of toxicity
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what happens in LA toxicity?
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*block Na channels
*affect AP throughout body *ability for systemic toxicity *toxicity proportionate to potency |
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what are the s/s of LA toxicity?
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*circumoral numbness
*metallic taste *tongue parasthesia *dizziness *tinnitus *blurred vision *restlessness/nervousness *agitation/paranoia *slurred speech *change of LOC *muscle twitching *resp arrest *CV collapse (r/t K/Ca channels) |
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what is the tx for LA toxicity?
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BZD (inc szr threshold)
O2 hyperventilate (dec CBF & drug exposure) |
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what terminates szr activity in LA toxicity?
|
pentothal 1-2mg/kg
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epidural vs subarachnoid blocks?
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*epidural is a volume block
*subarachnoid is a concentration block |
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which produce allergic rxns?
|
esters
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what is the MOA of LAs?
|
block nerve conduction pathways by blocking Na channels
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how can you tell if the pt has a successful block?
|
nerve fibers are blocked in a specific sequence
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what is the onset of action r/t in LAs?
|
pKa
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what is the DOA r/t in LAs?
|
protein binding
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what is the potency r/t in LAs?
|
lipid solubility
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