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61 Cards in this Set

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How do LA work?
By blocking sodium channels, which doesn't allow membrane depolarization.
It slows the impulse conduction, thereby decreasing the action potential.
It then increases the threshold for excitation until no action potential can be generated.
What does LA potency correlate with?
Lipid solubility
What does local onset of action correlate with?
lipid solubility (less soluble = faster onset)
Local concentration (higher concentration = faster onset)
pKa (lower pKa = faster onset)
addition of NaHCO3 (increases onset)
What does LA duration of action correlate with?
Lipid solubility (high solubility = long duration)
Addition of epinephrine, neosynephrine, clonidine
How are esters metabolized?
pseudocholinesterase / plasma cholinesterase
(temperature & pH dependent)
How are Amides metabolized?
P-450 enzyme of the liver
What are the early signs of local toxicity?
circumoral numbness, tongue paresthesia, dizziness, tinnitus, blurred vision.
The resting membrane potential in excitable tissues is determined by what?
potassium, all other ions are impermeable in the resting neuron because sodium and calcium channels are closed.
What is the treatment of methemoglobinemia?
Methylene blue (1-2mg/kg IV)
What are the risk factors for transient neurolgic symptoms?
Lidocaine, lithotomy position, obesity, outpatient status
What are the predisposing risk factors for bupivacaine induced cardiovascular toxicity?
Pregnancy, hypoxemia, respiratory acidosis, young children
What are the differences between bupivacaine and ropivacaine?
Ropivacaine is less lipid soluble and has less motor blockade. It has a larger therapeutic range and is 70% less likely to cause severe cardiac arrhythmias
What are LAs impact on ND-neuromuscular blockers?
LA potentiate them.
What is the preferred drug treatment for LA induced ventricular tachyarrhythmias?
Amioderone or bretylium
In what state do LA "lock" the sodium channel thereby preventing the impulse?
When the sodium channels are in the inactivated state after depolarization. Its called the Absolute Refractory Period.
What is the likely site of nerve entrence for local anesthetics in myelinated nerves?
the nodes of Ranvier.
Which two LAs cause vasoconstriction?
Ropivacaine and cocaine
How does epinephrine increase the duration of action of LAs?
The vasoconstricting properties reduce the rate of vascular absorption.
Which class of locals has a greater potential to cause an allergic reaction?
Esters, because of the metabolite para-aminobenzoic acid (PABA).
What physiological factors antagonize local blockade?
Acidic pH, hypokalemia, hypercalcemia
What is tachyphylaxis?
It is the decreased efficacy of drugs when giving repeated doses.
Which patients are at increased risk for local toxicity with esters?
Those with abnormal psudocholinesterase / plasma cholinesterase
List these amides in order of duration of action: lidocaine, bupivacaine, ropivacaine, prilocaine, mepivacaine.
Prilocaine, Lidocaine, Mepivacaine, Ropivacaine, Bupivacaine
Which drugs may cause methemoglobinemia?
Prilocaine & Benzocaine
How many mg of 0.75% Bupivacaine is in 2 mls?
15mg
What is the maximum dose of Lidocaine with and without epi?
4mg/kg without epi
7mg/kg with epi
What concentrations does lidocaine come in?
0.25% - 4%
What is the OOA & DOA of Lidocaine?
Fast onset
intermediate duration (60-120min)
What is the OOA & DOA of Mepivacaine?
Fast onset
intermediate duration (90-180min)
What is the OOA and DOA of Etidocaine?
Fast onset (??slow)
Long duration (4-8hrs)
Which LAs are commonly used for epidurals?
Lidocaine, Bupivacaine, Ropivacaine, Chlorprocaine
Which LAs are commonly used for spinals?
Bupivacaine, Tetracaine
What is the OOA and DOA of Prilocaine?
Fast onset (??slow)
Intermediate duration (60-120min)
What is the OOA and DOA of Bupivacaine?
intermediate onset
Long duration (4-8hrs)
WHat is the maximum dose of Prilocaine?
600mg single injection
What is the maximum dose of Bupivacaine?
3mg/kg or 175mg single dose w/o epi
225mg single does w/epi
What is the OOA and DOA of Ropivacaine?
Slow onset
Long duration (4-8hrs)
What is the maximum single dose of Ropivacaine?
200mg
What is the OOA and DOA of Cocaine?
Fast onset
Short duration
What is the mechanism of action of cocaine?
blocks the reuptake of norepinephrine and dopamine
How is cocaine metabolized?
by plasma cholinesterase
What is the OOA and DOA of Procaine (Novacaine)?
Slow onset
Short duration (45-60min)
What is the OOA and DOA of Chloroprocaine (Nesacaine)?
Fast onset
Short duration (30-45min)
What is the benefit of using Chlorprocaine for urgent c-sections?
It has a very rapid onset for epidural use, but must be followed with a longer acting local. The can start cutting sooner.
What is the OOA and DOA of Tetracaine?
Slow onset
Long duration (1-3hrs)
What is the maximum single dose of tetracaine?
20mg
What is the OOA and DOA of Benzocaine?
Fast onset
Short duration (30-60min)
At doses greater than 300mg Benzocaine can cause what?
Methemoglobinemia
Which local is the only one that is a weak acid vs. being a weak base?
Benzocaine, all others are weak bases.
That is why it is only used for topical anesthesia.
Which two LAs are generally used in EMLA cream?
Prilocaine and Lidocaine
What is the concentration and dose of epinephrine that is used in LAs to prolong DOA?
1:200,000
0.2mg
What is the procedure for a Bier Block?
Start IV in distal extremity
Inflate tourniquet (should not be able to draw blood from IV)
0.5% Lidocaine is injected into IV (3mg/kg)
After min. of 20min tourniquet is released
What are the principle sites of action for Spinal Anesthesia?
The superficial layers of the spinal cord and the preganglionic fibers
In local toxicity the seizure threshold is inversly related to what?
PaCO2, hyperventilation decreases CO2 thereby increaseing the seizure threshold (less likely to have seizures)
What does hypokalemia and hyperkalemia do LA toxicity?
Hypokalemia decreases toxicity
Hyperkalemia increases toxicity
List the following in order of first occuring to last occuring with local toxicity: Circumoral & tongue numbness, convulsions, CVS depression, Visual disturbances, Coma, Muscle twitiching, Respiratory arrest, unconsiousness
circumoral & tongue numbess
visual disturbances
muscle twitiching
convulsions
unconsiousness
coma
respiratory arrest
CVS depression
What is the dose of lipid for cardiotoxicity treatment?
20% Lipids - 1.5ml/kg bolus
then 0.25ml/kg
* can repeat bolus 2 times at 5min intervalls
* can increase infusion to 0.5ml/kg
What nerve fibers carry pain signals to the brain?
Afferent nerve fibers. A-delta and C fibers
What is the resting membrane potential in the neuron?
-70mV
What occurs with the sodium channels during depolarization?
Sodium channel snaps open and sodium flows inward.
What part of the alph subunit do locals bind to?
H subunit