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320 Cards in this Set

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Name the 5 "ester" Local Anesthetics
Procaine (Novacaine), Chloroprocaine (Nesacaine), Tetracaine (Pontocaine), Benzocaine (Hurricane Spray), Cocaine
Name the 6 "amide" Local Anesthetics
Lidocaine (Xylocaine), Mepivacaine (Carbocaine), Prilocaine (Citanest), Bupivacaine (Marcaine), Ropivacaine (Naropin), Levobupivacaine (Chirocaine)
What type of nerve fibers are continuously encased by Schwann cells without interruption?
Unmyelinated Fibers
Which type of nerve fibers has a myelin covering that is interrupted by nodes of Ranvier, allowing the passage of drugs and ions?
Myelinated nerve fibers
In Myelinated nerve fibers, impulse propagation occurs where?
Nodes of Ranvier
Following a peripheral nerve block, what percentage of the dose reaches the nerve?
<2%
What 2 nerve characteristics result in more rapid conduction?
increased myelination and increased nerve diameter
Which 2 nerve fiber types are myelinated?
Type A and Type B
Which nerve fiber type is unmyelinated?
Type C
Type A nerve fiber is the only type with 4 subtypes; What are the subtypes?
Alpha, Beta, Gamma and Delta
What is the resting membrane potential?
-90 mv
What is the resting membrane potential maintained by?
ATP dependent pump which expels Na+ in exchange for K+ via voltage-gated K+ channels
What is the threshold potential?
-65 mv
What does the generation of an action potential rely on?
Activation of voltage-gated Na+ channels in sufficient number to reach threshold potential of -65mv
What's the general effect of Local Anesthetics on generation of an action potential?
They don't allow enough Na+ channels to open to generate an action potential
Are Local Anesthetics mainly weak acids or weak bases?
Weak Bases
Tonic or Phasic Inhibition? "Time between action potentials exceeds time for dissociation of local anesthetic from the Na+ channel"
Tonic
Why is it crucial for Local Anesthetics to be lipophilic?
They must traverse the lipid membrane to affect Na+ channel from the intracellular side
What kind of hydrophobicity results in more rapid onset of the Local Anesthetic, Poorly, moderately or extremely hydrophobic Local Anesthetic?
Moderately hydrophobic
Potency is directly related to ________.
Hydrophobicity
Which LA has a "low potency?"
Procaine
Which LAs have an "intermediate potency?"
Mepivacaine, Prilocaine, Chloroprocaine, Lidocaine
Which LAs have a "high potency?"
Tetracaine, Bupivacaine, Etidocaine
What form (charged, hydrophilic or lipid soluble neutral) must LA be in before it can directly inhibit the Na+ channel?
Charged, hydrophilic form (must be reprotonated after enters through lipid membrane)
Na+ channels have many conformations; which conformation has a low affinity for LAs?
Resting Conformation
What Na+ channel conformation has the highest affinity for LAs?
Open conformation
Which type of inhibition, tonic or phasic, is defined as "time between action potentials is less than time needed for local anesthetic to dissociate from Na+ channel?"
Phasic
Which type of inhibition, tonic or phasic, can more rapidly build a better block?
Phasic Inhibition
Which nerve fibers are MOST susceptible to local anesthetic block?
Small, myelinated (Aγ Motor and Aδ sensory)
Which nerve fibers are intermediately susceptible to local anesthetic block?
Large, myelinated (Aα and Aβ)
Which nerve fibers are LEAST susceptible to local anesthetic block?
Small, non-myelinated (C)
What are some situations in which rate of Neural firing is high or abnormal repetitive firing occurs?
Tissue injury or trauma, various disease states such as neuropathic pain
How can you use local anesthetics to treat situations in which rate of neural firing or abnormal repetitive firing occurs?
May often be treated with local anesthetic concentrations lower than necessary to block normal nerves (by taking advantage of Phasic inhibition)
Increasing concentrations of local anesthetic will usually produce blockade in what sequence?
Autonomic (preganglionic sympathetics), Sensory (Pain, temperature), Motor (large motor)
Sympathetic, sensory, and motor block will reach _____ levels following central neuraxis anesthesia
different
How can you determine where the SNS block is located in a particular patient?
Run your hand lightly up the side of the patient; where skin gets "sticky" is where the SNS block is
Sensory block is located approximately ____ Dermatomes ____ SNS block
2 Dermatomes BELOW
Motor block is located approximately ____ Dermatomes ____ sensory block
2 Dermatomes BELOW
Chemically, what do all local anesthetics consist of?
a Hydrophobic aromatic ring joined by an ester OR amide bond to a hydrophilic amine
What are the determinants of Local Anesthetic Onset, Duration, and Potency?
pKa, lipid solubility, protein binding, concentration and vasoconstrictive or vasodilatory properties
Only the _____ form of the LA may penetrate the lipid membrane
Neutral (lipophilic)
Percentage of LA drug in neutral (lipophilic) form is inversely proportional to the pKa; therefore, a ______ pKa equates to a more rapid onset
LOWER
Net result of INCREASED lipid solubility of LA drugs is ______ onset of action
DELAYED
Why does increased lipid solubility of LAs delay the onset of action?
While increased lipid solubility allows the drug to pentrate the lipid membrane more rapidly, increased lipid solubility may also result in the drug being "stuck" in myelin and other lipid-soluble compartments, including the axonal membrane itself; "stuck" drug is less able to get to the site of action, delaying onset
What factor causes an increased DURATION of action of LAs?
Slow release of drug from the lipid depot
Potency parallels _______.
Lipid solubility
The more lipid soluble the LA is, the (higher/lower) the Na+ channel receptor affinity?
Higher
What effect do lipid soluble LAs have on the Na+ channel?
Ability to alter conformation of Na+ channel through direct membrane altering effects
Increased protein binding of LAs is asscoiated with increased _________.
Duration of action (not able to be metabolized)
Increasing dose/concentration of LAs results in (more rapid onset, less rapid onset, or no change in onset) of action?
More rapid onset (Ex. 3% Chloroprocaine will have a faster onset than 2%)
Other than slow release from lipid depot and protein binding, what's another property that plays a major role in determining DURATION of ACTION of LAs?
Vasoactive properties
MOST are (Vasodilators, vasoconstrictors) at clinically useful concentration?
Vasodilators
Most LAs are vasodilators; what are 3 exceptions to this?
Cocaine, Ropivacaine, and Levobupivacaine
Why are Ropivacaine and Levobupivacaine vasoconstrictors?
They are both supplied as S-enantiomers, which have inherent vasoconstrictive activity
How does Vasodilation effect the duration of action of LAs?
The more potent vasodilator drugs cause more blood flow, which washes out the drug more quickly
Lidocaine is a more potent vasodilator than _______ (drug) and has a duration of 30-60 minutes; will (the other drug) have a shorter or longer duration of action than Lidocaine?
Prilocaine; Longer duraton of action (because it's a less potent vasodilator--less washout of drug)
What are the benefits of adding a vasoconstrictor to a LA that vasodilates?
Decreases the rate of vascular absorption, creating a denser block (more drug reaches the site of action) and prolongs the duration of action (decreased clearance of drug from site of injection--not getting "washed" out)
Adding vasoconstrictors to the LA (peripheral nerve block) regimen is most effective with drugs of ______ to ______ duration
Short to moderate
What is most commonly given as a vasoconstrictor in conjunction with LAs?
Epinephrine (5 mcg/ml)
What are 2 vasoconstrictors (other than Epinephrine) that are given in conjunction with LAs?
Phenylephrine and Norepinephrine
What sites should you avoid injecting a vasoconstrictor?
sites which may experience vascular compromise (distal extremities, etc)
Adjusting the pH of the LA via ALKALINIZATION may produce what effects?
Speed up the onset of the block, provide a greater depth of block and increase the spread of epidural block
What mechanism occurs when the pH of a LA is adjusted and made more alkaline?
Increases the percentage of drug existing in the neutral (lipid soluble) form which may rapidly diffuse across the neural membrane
What is the appropriate "technique" for making the LA more alkaline?
Addition of 1 ml of sodium bicarbonate to 10 ml of Local
What is important to remember regarding LAs prepackaged with Epinephrine in regards to pH?
the pH of LAs prepackaged with Epinephrine is is Lower than normal to extend the shelf life of Epinephrine
Toxicity when giving multiple LA drugs (mixture) is _______
Additive
When administering a "mixture" of multiple LAs, should you give (maximum dose, lower dose) of each agent in the mixture?
You have to administer lower doses of each agent in the mixture; effects are additive and toxicity can occur
Binding of the LA to the Na+ channel occurs primarily from the ______ side of the neural membrane
Intracellular
Some alteration of the Na+ channel may occur from within the lipid membrane, particularly in the case of the highly _______, highly ______ local anesthetics
Lipophilic, Potent
What's the problem with administering an EXTREMELY hydrophobic (lipophilic) LA?
An extremely hydrophobic LA molecule will rapidly enter the lipid membrane, but may become "stuck" there, unable to reach the intracellular side, therefore having a SLOWER onset of action
What's the benefit of administering a LA that is "moderately" hydrophobic?
A moderately hydrophobic LA can enter the lipid membrane relatively quickly, and can also exit the membrane to the intracellular side to interact with the sodium channel--therefore has a faster onset of action
A highly hydrophobic LA has a ______ affinity for the Sodium channel; what does this mean?
HIGH; this means it stays bound to the Na+ channel longer
Lower pKa=more non-ionized drug=???
Faster Onset of action
Increased lipid solubility=???
increased duration of action and increased potency
Increased protein binding=???
Increased Duration of action
Increased Concentration=???
More rapid onset
Increased dose=???
Increased Duration of action
Increased vasodilatory properties=???
Decreased Duration (because increased blood flow and more anesthetic washout)
Addition of Epinephrine (vasoconstrictor) is more effective in increasing the duration following infiltration and peripheral nerve blocks than following ___________.
Central Neuraxis anesthesia (spinal, epidural)
The injection of LA into infected (acidotic) tissue will be relatively _______
ineffective (will become ionized fairly quickly and unable to cross the neural membrane)
Why is alkalinizing the LA solution a good idea before injecting the LA via IV?
Alkalinization of LA solution may also reduce the burning of injection caused by the acidic pH of the drugs (in a solution)
Which LA is the first injectable LA?
Procaine (Novacaine) (Ester)
Procaine (Novacaine) is a derivative of para-aminobenzoic acid; what is significant about this fact?
There are allergy complications with it
Does Procaine (Novacaine) have a high or low pKa? Does it have poor or good lipid solubility?
High pKa; poor lipid solubility
Because Procaine (Novacaine) has a high pKa with poor lipid solubility, what does this implicate about its onset and duration of action?
Slow onset and short duration of action (30-60 minutes)
What are the 2 main side effects/complications of Procaine (Novacaine)?
high incidence of nausea and increased potential for allergic reactions
Is Procaine (Novacaine) used frequently or rarely used anymore?
Rarely used
Which LA is a derivative of Procaine?
Chloroprocaine (Nesacaine) (ester)
Which LA has the most rapid metabolism?
Chloroprocaine (Nesacaine) (ester) (plasma half-life = <30 seconds
Which LA is primarily used as an epidural anesthetic for C-section?
Chloroprocaine (Nesacaine)
Why is Chloroprocaine beneficial for epidural anesthesia for a C-section?
Rapid onset, short duration and limited potential for systemic toxicity
What undesirable effect does Chloroprocaine (Nesacaine) have on analgesia?
Reduces the analgesic effect of concurrently, or subsequently administered Bupivacaine and Opioids
Which LA is used primarily in topical (opthlamologic) and spinal anesthesia?
Tetracaine (Pontocaine) (ester)
Is Tetracaine (Pontocaine) highly lipophilic or poorly lipophilic?
Highly
Which LA has a slow rate of metabolism (for an ester)?
Tetracaine (Pontocaine)
Tetracaine (Pontocaine) has a long duration of action. Why?
Highly Lipophilic, highly protein bound, slow metabolism (for an ester)
In relation to the receptor, because Tetracaine (Pontocaine) is very lipophilic it is also highly ______
POTENT
What 2 things do Tetracaine (Pontcaine) block?
Profound Sensory and Motor block
Tetracaine (Pontocaine) is supplied as a crystalline form; this allows it to be more stable and allows for variation in ________.
Baricity
What makes Benzocaine (Hurricane) (ester) unique from the other LAs?
It's a weak acid
What's the pKa of Benzocaine (Hurricane)?
3.5
Which LA is best suited and most often used for topicalization of mucous membranes?
Benzocaine (Hurricane) (ester)
Does Benzocaine (Hurricane) have a rapid or delayed onset of action?
EXTREMELY rapid onset
How long is the duration of action of Benzocaine (Hurricane)?
30-60 minutes
Which LA has the potential to produce methemoglobinemia (esp. in neonates and doses exceeding ~300mg)?
Benzocaine (Hurricane) (ester)
Which ester LA produces INTENSE Vasoconstriction?
Cocaine
Which LA is used as a 4% or 10% solution for nasopharyngeal topicalization prior to surgery or other instrumentation?
Cocaine
Which ester LA has a LOW therapeutic index (least safe)?
Cocaine
Which ester LA has a high abuse potential?
Cocaine
What's the brand name for Procaine?
Novacaine
What's the generic name for Novacaine?
Procaine
What's the brand name for Chloroprocaine?
Nesacaine
What's ther generic name for Nesacaine?
Chloroprocaine
What's the brand name for Tetracaine?
Pontocaine
What's the generic name for Pontocaine?
Tetracaine
What's the brand name for Benzocaine?
Hurricane
What's the generic name for Hurricane?
Benzocaine
What's the brand name for Lidocaine?
Xylocaine
What's the generic name for Xylocaine?
Lidocaine
Is Lidocaine (Xylocaine) an amide or an ester?
Amide
Which amide LA was the first aminoamide introduced and most widely used?
Lidocaine (Xylocaine)
Is Cocaine an amide or an ester?
Ester
Is Procaine (Novacaine) an amide or an ester?
Ester
Is Chloroprocaine (Nesacaine)an amide or an ester?
Ester
Is Tetracaine (Pontocaine) an amide or an ester?
Ester
Is Benzocaine (Hurricane) an amide or an ester?
Ester
Which amide LA has a rapid onset, intermediate duration of action and a broad range of uses?
Lidocaine (Xylocaine)
Does Lidocaine (Xylocaine) have a rapid or slow onset of action?
Rapid
Lidocaine has many uses (including infiltration); what type of Lidocaine solution (percent) is used for infiltration and how long is the duration of action?
0.5-1.0% solution; Duration of action is 30-60 minutes
When Lidocaine (Xylocaine) is used as topical anesthesia of mucous membranes, what type of Lidocaine solution is used (percent) and what type of drug is administered with it?
Typically a 4% solution; used in combination with a vasoconstrictor
What type of surgery is "Tumescent anesthesia" associated with?
Liposuction
Is Lidocaine often used for epidural (central neuraxis) anesthesia?
YES
Which amide LA is the most commonly used drug for the Bier Block (IV regional block)?
Lidocaine (Xylocaine)
Does Lidocaine (Xylocaine) blunt the hemodynamic response to intubation?
YES
Which route of Lidocaine administration is most effective when used for intubation: Laryngotracheal spray or Intravenous? Why?
Intravenous; spray may not have enough time to work before ET tube is placed
In addition to blunting the HD response to intubation, what other effects are attenuated associated with tracheal instrumentation?
attenuates increases in IOP, ICP, and intra-abdominal pressure associated with tracheal instrumentation
What unique use does Lidocaine (Xylocaine) have in association with the heart?
Antidysrhythmic
How does Lidocaine (Xylocaine) help with chronic neuropathic pain?
Low doses are effective in blocking increased ectopic discharges in a damaged nerve, possibly through inhibition of hippocampal and thalamic neurons
What is the brand name of the LA amide Mepivacaine?
Carbacaine
What is the generic name for the LA amide, Carbacaine?
Mepivacaine
Which 2 drugs are very similar to Lidocaine (Xylocaine)?
Mepivacaine (Carbacaine) and Prilocaine (Citanest)
Which amide LA is very similar to Lidocaine (Xylocaine) but slightly less potent with a slightly longer duration of action?
Mepivacaine (Carbacaine)
Which 2 ester LAs most similar to Lidocaine (Xylocaine) produce less vasodilation, so therefore less need for a vasoconstrictor?
Mepivacaine (Carbacaine) and Prilocaine (Citanest)
What is Mepivacaine (Carbacaine) primarily used for?
Peripheral nerve block
What concentration (percent) of Mepivacaine (Carbacaine) is used for peripheral nerve block and what's the duration of action?
1-1.5% solution; duration of action is 2-4 hours
Which amide LA is poorly metabolized by a fetus and accumulation may lead to poor fetal muscle tone?
Mepivacaine (Carbacaine)
Which amide LA should you avoid using in OB as an epidural due to its negative effects on the fetus?
Mepivacaine (Carbacaine)
What's the Brand name of the LA amide Prilocaine?
Citanest
What's the generic name for Citanest?
Prilocaine
Is Mepivacaine (Carbacaine) an ester or an amide LA?
Amide
Is Prilocaine (Citanest) an Ester or an amide LA?
Amide
Which amide LA is very similar to Lidocaine (Xylocaine) except it is more rapidly metabolized, has decreased CNS toxicity and causes less vasodilation?
Prilocaine (Citanest)
What is the metabolite of Prilocaine (Citanest) that at large doses can accumulate and produce methemoglobinemia?
Orthotoluidine
At what dose can the metabolite of Prilocaine accumulate and cause methemoglobinemia?
Large dose (>600 mg)
What does Prilocaine's metabolite Orthotoluidine produce in large doses (>600 mg)
methemoglobinemia
Which amide LA is used most commonly in equal parts with Lidocaine (Xylocaine) as EMLA cream?
Prilocaine (Citanest)
What's the brand name for Bupivacaine?
Marcaine
What's the generic name for Marcaine?
Bupivacaine
Is Bupivacaine (Marcaine) and ester or an amide LA?
Amide
Does Bupivacaine have a fast or slow onset? Duration of action?
Slow onset; prolonged duration of action
With Bupivacaine (Marcaine) at concentrations below _____% sensory block is greater than motor block
0.25%
What are 2 indications for using 0.25% concentration of Bupivacaine (Marcaine) (causing a greater sensory block than motor block?
Labor analgesia, Post-operative pain management
What is considered to be the largest complication/side effect of Bupivacaine (Marcaine)?
Cardiotoxicity
What are the 3 uses of Bupivacaine (Marcaine)?
Spinal anesthesia, Epidural anesthesia and peripheral nerve block
Bupivacaine (Marcaine) has a slow onset in most all cases except ______.
with spinal and infiltration anesthesia
When used as spinal anesthesia, does Bupivacaine have a slow or a rapid onset of action? What is it?
Rapid; ~5 minutes
What is the duration of action of Bupivacaine when used as spinal anesthesia?
~1-4 hours (dose dependent)
Which amide LA is the most common drug used for spinal anesthesia?
Bupivacaine (Marcaine)
What concentration do you use with Bupivacaine (Marcaine) when using it for an epidural?
<0.1%-0.5% depending on depth of anesthesia needed
Which concentration of Bupivacaine (Marcaine) works for most people in keeping them comfortable (epidural)?
0.1%
What percentage % concentration of Bupivacaine (Marcaine) is no longer recommended due to its potential for cardiac toxicity?
0.75%
What is extremely important to remember regarding the injection of Bupivacaine (Marcaine)?
INCREMENTAL injection is extremely important
What's the brand name for Ropivacaine?
Naropin
What's the generic name for Naropin?
Ropivacaine
Is Ropivacaine (Naropin) an amide or an ester?
Amide
Ropivacaine (Naropin) is similar in structure to which 2 amide LAs?
Bupivacaine (Marcaine) and Mepivacaine (Carbacaine)
What are 4 uses for Ropivacaine (Naropin)?
Epidural, Spinal, Peripheral Nerve Block, Brachial Plexus Block
What is unique about Ropivacaine (Naropin) among the amides?
causes vasoconstriction
What's the brand name for Levobupivacaine?
Chirocaine
What's the generic name for Chirocaine?
Levobupivacaine
Is Levobupivacaine (Chirocaine) an ester or an amide LA?
Amide
How does Levobupivacaine (Chirocaine) relate to Bupivacaine (Marcaine)?
It's the S(-) enantiomer of Bupivacaine
Levobupivacaine (Chirocaine) is similar to Bupivacaine except has a slightly _____ duration.
Longer
Levobupivacaine (Chirocaine) is known to have decreased cardiac and CNS toxicity; why?
Likely due to decreased affinity of Levobupivacaine for these tissues
What is beneficial of both Ropivacaine (Naropin) and Levobupivacaine (Chirocaine)?
both have decreased incidences of cardiac and CNS toxicity
Potency of a given local anesthetic varies with ____; what is the significance of this fact?
application; this may make certain drugs more appropriate for certain blocks
Which LA do you use for infiltration anesthesia?
Most LAs are effective
What are the 2 most commonly used LAs for infiltration anesthesia?
Lidocaine (xylocaine) and Bupivacaine (Marcaine)
What concentration of Lidocaine (Xylocaine) do you typically use for infiltration anesthesia? What's the max DOSE?
Typically 0.5-1%; Max DOSE=5 mg/kg; with epinephrine=7 mg/kg
What's the concentration of Bupivacaine (Marcaine) used for infiltration anesthesia? What's the max DOSE?
Typically 0.25-0.5%; Max DOSE= 2mg/kg; with epinephrine= 3mg/kg
What can be added to infiltration anesthesia to reduce the burning on injection (particularly valuable in children)?
Addition of Neutracaine (sodium bicarbonate)
A plain 0.5-1% solution of Lidocaine has a duration of how long?
30-60 minutes
What's the max dose of Lidocaine (plain solution) in mg?
300 mg
An epinephrine-containing solution of Lidocaine (0.5-1%) has a duration of how long?
120 minutes
What's the max dose of Lidocaine (epinephrine-containing solution) in mg?
500 mg
Plain solution Bupivacaine (Marcaine) (0.25-0.5%) has a duration of action of how long?
120-240 minutes
What's the max dose of plain solution Bupivacaine (Marcaine) in mg?
175 mg
Epinephrine-containing solution of Bupivacaine (Marcaine) has a duration of action of how long?
180 minutes
What's the max dose of epinephrine-containing solution of Bupivocaine in mg?
225 mg
What is the most common LA used for a BIER Block?
Lidocaine (xylocaine)
Is Lidocaine given with or without Epinephrine when performing a BIER Block?
Without Epinephrine
When performing a BIER Block with Lidocaine (Xylocaine) what concentration and dosage do you use in an UPPER extremity?
Concentration=0.5% solution;
Dosage=40-50ml
When performing a BIER Block with Lidocaine (Xylocaine), what concentration and dosage do you use in a LOWER extremity (calf)?
concentration=0.25% solution;
Dosage=50-100 ml
Why do you not use ester LAs for a BIER Block?
Potential for thrombophlebitis with the ester LAs
What's considered a "minor" peripheral nerve block?
blocking a single nerve
What's considered "major" peripheral nerve blocks?
Blocking 2 or more nerves or blocking a nerve plexus
What determines which LA drug to use for a peripheral nerve block?
Duration of block required
For "single shot" epidural techniques, what is a very important consideration?
Duration of action
When using epidural CATHETER techniques, what are very important considerations?
speed of onset of action, and characteristics of the block
Which drug, when given with short and intermediate acting LAs, produces an increase in duration of action?
Epinephrine
Which drug, when used as epidural anesthesia, produces greater sensory than motor block at lower concentrations?
Bupivacaine (Marcaine)
Which drug decreases the effectiveness of concurrent or subsequent adminstration of Bupivacaine (Marcaine) or opioids via epidural?
Chloroprocaine (Nesacaine)
What are 3 considerations for Spinal anesthesia?
Duration, Baricity and Toxicity
Which is more reliable, hyperbaricity or hypobaricity?
Hyperbaricity
What are 3 uses of EMLA for topical anesthesia?
IV starts, Skin grafting, Circumcision
What are 4 indications of topical anesthesia of mucosal membranes?
Bronchoscopy, Endoscopy, Nasal surgery, Intubation
What does "tumescent anesthesia" include?
Large volumes of dilute local anesthetic with epinephrine
Which LA and concentration (%) is typically used for Tumescent anesthesia?
Lidocaine--0.1% or less (dilute)
What other drug is given with Lidocaine in Tumescent anesthesia? What concentration?
Epinephrine--1:1,000,000
What DOSE of Lidocaine (Xylocaine) do you administer with tumescent anesthesia?
Up to 35-55 mg/kg
Why does delayed absorption occur in tumescent anesthesia? What does this mean?
Delayed absorption occurs because drug gets stored in the fat; peak blood levels at 11-15 hours after injection; prolonged analgesia of 18-24 hours in some patients
What's tachyphylaxis?
Decreased response to a repeated injection of the same dose
True/False: If dosing intervals are short enough that pain doesn't recur, tachyphylaxis doesn't develop
TRUE
TRUE/FALSE: The longer the periods of pain allowed before redosing, the more slowly tachyphylaxis occurs
FALSE; the more rapidly tachyphylaxis occurs
What is thought to be the mechanism behind tachyphylaxis?
thought to be due to a central mechanism, i.e. spinal cord sensitization
Which ester LA is metabolized the fastest?
Chloroprocaine (Nesacaine)
Which ester LA is metabolized the slowest?
Tetracaine (Pontocaine)
How are ester LAs metabolized?
hydrolysis of the ester bond by plasma cholinesterase
How are amide LAs metabolized?
Via enzymatic degradation in the Liver and by renal excretion of metabolites
Because amide LAs are degraded in the Liver, what 4 things does this metabolism depend on?
Hepatic extraction, Hepatic perfusion, Hepatic metabolism, and Protein Binding
What's the initial step of liver metabolism of Amide LAs?
Oxidative dealkylation
What factors decrease clearance of Amide LAs?
Hepatic dysfunction, PIH (Pregnancy-induced HTN), and presence of volatile anesthetics (decreases liver blood flow and therefore decreases metabolism)
Pulmonary extraction of which 3 amide LAs limits the concentration reaching the systemic circulation?
Lidocaine, Bupivacaine, and Prilocaine
What does "Lung Extraction" do?
Moderates the potential for systemic toxicity by reducing the amount reaching the cerebral and coronary vessels
What drug inhibits Pulmonary Extraction?
Propranolol
Many people report _____ to local anesthetics
Allergy
Of the allergic reactions to LAs reported, fewer than ____% are true allergic reactions
1%
Which group of LAs, the esters or the amides, have the highest incidence of reported allergic reactions? Why?
Esters; metabolism of esters results in compounds related to PABA
Patients may experience allergic reactions from ______ in both amide and ester solutions
preservatives
What are 3 uses of EMLA for topical anesthesia?
IV starts, Skin grafting, Circumcision
What are 4 indications of topical anesthesia of mucosal membranes?
Bronchoscopy, Endoscopy, Nasal surgery, Intubation
What does "tumescent anesthesia" include?
Large volumes of dilute local anesthetic with epinephrine
Which LA and concentration (%) is typically used for Tumescent anesthesia?
Lidocaine--0.1% or less (dilute)
What other drug is given with Lidocaine in Tumescent anesthesia? What concentration?
Epinephrine--1:1,000,000
What are 3 uses of EMLA for topical anesthesia?
IV starts, Skin grafting, Circumcision
What are 4 indications of topical anesthesia of mucosal membranes?
Bronchoscopy, Endoscopy, Nasal surgery, Intubation
What does "tumescent anesthesia" include?
Large volumes of dilute local anesthetic with epinephrine
Which LA and concentration (%) is typically used for Tumescent anesthesia?
Lidocaine--0.1% or less (dilute)
What other drug is given with Lidocaine in Tumescent anesthesia? What concentration?
Epinephrine--1:1,000,000
Which drug, when given with short and intermediate acting LAs, produces an increase in duration of action?
Epinephrine
Which drug, when used as epidural anesthesia, produces greater sensory than motor block at lower concentrations?
Bupivacaine (Marcaine)
Which drug decreases the effectiveness of concurrent or subsequent adminstration of Bupivacaine (Marcaine) or opioids via epidural?
Chloroprocaine (Nesacaine)
What are 3 considerations for Spinal anesthesia?
Duration, Baricity and Toxicity
Which is more reliable, hyperbaricity or hypobaricity?
Hyperbaricity
What's considered a "minor" peripheral nerve block?
blocking a single nerve
What's considered "major" peripheral nerve blocks?
Blocking 2 or more nerves or blocking a nerve plexus
What determines which LA drug to use for a peripheral nerve block?
Duration of block required
For "single shot" epidural techniques, what is a very important consideration?
Duration of action
When using epidural CATHETER techniques, what are very important considerations?
speed of onset of action, and characteristics of the block
What's considered a "minor" peripheral nerve block?
blocking a single nerve
What's considered "major" peripheral nerve blocks?
Blocking 2 or more nerves or blocking a nerve plexus
What determines which LA drug to use for a peripheral nerve block?
Duration of block required
For "single shot" epidural techniques, what is a very important consideration?
Duration of action
When using epidural CATHETER techniques, what are very important considerations?
speed of onset of action, and characteristics of the block
What 5 things does ABSORPTION of LAs depend on?
Vascularity of injection site, Fat content of injection site (slows absorption), Dose of Local Anesthetic, Physiochemical properties of the drug, and Presence of a vasoconstrictor
How do they "Physiochemical Properties" of LAs effect their absorption?
More potent agents have higher lipid solubility and protein binding resulting in less systemic absorption
What 5 things does "ICEBS" stand for?
I=intercostal; C=Caudal, E=Epidural, B=Brachial Plexus, S=Sciatic femoral
What's the order of effect in regards to blood levels of LAs?
ICEBS
There's a new LA technique called "Liposomal Encapsulation;" What's the benefit of this technique?
Slow, extended release; longer duration; reduced toxicity
What mechanism causes LA neurotoxicity?
Exposure to desheathed nerve to high concentrations of LA results in injury
What is important to be mindful of in regards to LA injection and neurotoxicity?
Be careful; do not inject LA into a site where parasthesias exist; back needle out
Which is more prone to injury, peripheral nerves or spinal cord and nerve root?
Spinal cord and nerve root
What are the signs of LA neurotoxicity?
Non-specific patchy numbness, Transient Neurologic Symptoms (TNS), and Cauda Equina Syndrome (it is unclear whether these are distinct entities or a spectrum of severity of the same underlying injury
True/False: Permanent neurologic injury following regional anesthesia is a fairly common occurrence
FALSE; it is an extremely RARE occurrence
What are the Transient Neurologic Symptoms (TNS) after spinal anesthesia?
Moderate to severe pain in the lower back, buttocks, and posterior thighs
When do Transient Neurologic Symptoms (TNS) typically occur?
Usually noted within 6-24 hours of resolution of the block (fairly quickly postop)
When attempting to diagnose "Transient Neurologic Symptoms" is the sensory and motor exam normal or abnormal?
NORMAL
How long does it take to recover from Transient Neurologic Symptoms (TNS)?
Full recovery typically within 1-7 days
Since Transient Neurologic Symptoms (TNS) often require pain management in the interim (between onset and recovery), what types of pain management are used?
NSAIDs, trigger point injections and Opioids
Which LAs cause the highest incidence of Transient Neurologic Symptoms (TNS)?
Incidence is highest following intrathecal (spinal and subarrachnoid) LIDOCAINE (Xylocaine) and Mepivacaine (Carbacaine)
Does incidence of Transient Neurologic Symptoms (TNS)decrease by using a smaller concentration of LA?
NO
Usage of ______ in spinal anesthesia produces a higher incidence of Transient Neurologic Symptoms (TNS)
spinal microcatheters
Why is it proposed that spinal microcatheters possibly increase the incidence of Transient Neurologic Symptoms (TNS)?
Possibly related to deposition of local in a small area without adequate mixing in CSF (not being rapidly washed away; increased concentration in a specific area over a prolonged time)
Which "procedure" offers the lowest incidence of Transient Neurologic Symptoms (TNS)?
C-section
Which body positioning offers the highest incidence of Transient Neurologic Symptoms (TNS)?
Highest incidence in Lithotomy and knee arthroscopy positions (due to increased amount of nerve stretch related to these positions)
What are the main 3 etiologic factors in developing Transient Neurologic Symptoms (TNS)?
Patient positioning, neural ischemia secondary to STRETCH, and Maldistribution of local anesthetic (pooling)
What is "Cauda Equina Syndrome?"
Diffuse injury across the Lumbosacral Plexus
What are 3 undesirable effects from "Cauda Equina Syndrome?"
Varying degrees of sensory loss, Bowel and bladder dysfunction and paraplegia
What are other causes of "Cauda Equina Syndrome" other than LA administration?
Trauma and Compression (hematoma, infection)
Why is it important to rule out "Cauda Equina Syndrome" before instituting symptomatic treatment for "Transient Neuronal Syndrome (TNS)?"
Don't want to mask with a bunch of Opioids and steroids in case it is an ischemic cord
Above what concentration of Lidocaine (Xylocaine) do you get increased CNS effects?
>5 mg/ml
Do LAs readily cross the blood-brain barrier?
YES
Are LA CNS effects dose dependent?
YES
What CNS effects do low plasma concentrations of LAs cause?
CNS depression
What CNS effects do moderate to high plasma concentrations of LAs cause?
CNS excitation, seizure activity
What CNS effects do HIGH plasma concentrations of LAs cause?
generalized CNS depression
Potential for CNS toxicity ______ drug potency
Parallels
What factors cause an increased potential for CNS toxicity?
Acidosis, Increased PCO2, decreased protein binding (more free drug available), decreased drug clearance, more rapid IV injection
What 2 drug classes decrease the potential for CNS toxicity from LAs?
Barbiturates and Benzos
Potential for CNS toxicity varies with ___________.
What type of block you're doing
Which type of block appears to have the highest incidence of CNS toxicity?
Peripheral nerve blocks (due to unintentional vascular injection)
Cardiac toxicity from LAs generally require a higher or lower plasma concentration than CNS toxicity?
HIGHER
Potential for cardiac toxicity _____ anesthetic potency
Parallels
Higher potency, more lipid-soluble agents have a greater or smaller inherent cardiotoxicity?
GREATER (increased affinity for Na+ channels)
Which 3 LAs have a higher potency (lipid solubilty) and therefore higher risk for cardiotoxicity?
Bupivacaine, Ropivacaine and Etidocaine
When you increase doses of the LESS potent agents (e.g. Lidocaine), what 3 CV effects generally occur?
Hypotension, Bradycardia, and Hypoxia
What is really scary about the CV effects of the MORE potent agents (e.g. Bupivacaine)?
The more potent agents more often result in SUDDEN cardiovascular collapse with ventricular dysrythmias which are resistant to resuscitation
Lidocaine and Bupivacaine have equivalent effects on myocardial _______.
contractility
Bupivacaine has a much _____ affinity for resting and inactive sodium channels than Lidocaine
HIGHER (it's more potent and more lipid soluble than Lidocaine)
Bupivacaine dissociates much more _____ than Lidocaine during diastole such that sodium channels never completely recover, and conduction block by Bupivacaine accumulates
SLOWLY
Threshold for Bupivacaine induced cardiac toxicity is _____ in pregnancy
REDUCED
Which 3 cardiac drugs decrease the threshold for cardiac toxicity with LAs?
Beta blockers, calcium channel blockers and Digoxin
Which 2 drugs are approximately equipotent to Bupivacaine for plexus anesthesia and nerve block?
Ropivacaine and Levobupivacaine
Why is it that Ropivacaine and Levobupivacaine have less CNS and Cardiac toxicity?
Preparation as single isomers may decrease affinity for brain and myocardium
True/False: Local Anesthetic-Induced Cardiotoxicity is difficult to treat
TRUE
Prevention is important in preventing LA-induced cardiotoxicity; what are 2 important aspects of prevention?
Careful assessment of appropriate dose and
Frequent aspiration=fractional injection
What are 4 ways to treat Cardiotoxicity if it occurs?
Maintenance of ventilation and oxygenation, pressure and rate support as necessary, management of ventricular dysrythmias, lipid therapy
Why is management of ventricular dysrythmias problematic in cardiotoxicity?
May be extended, may require large, and multiple doses of: Cardioversion, epinephrine, Vasopressin, and Amiodarone
What drug is NOT indicated in treatment of ventricular dysrythmias in LA cardiotoxicity?
Calcium channel blockers
What's the concentration and dosing requirements of lipid therapy used for treating cardiotoxicity?
20% lipid solution; bolus 4 ml/kg, followed by infusion of 0.5 ml/kg/min x 10 minutes