EXAM 3 -Local Anesthetics- COMP Flashcards
Comment on desirable characteristics of LA as far as OA, DOA, toxicity degree and reaction
Desirable characteristics are:
Very fast onset of action
Long duration of action
NO tachyphylaxis
What was the first Local anesthetics
Cocaine
What was the first synthetic ESTER
Procaine
Gold standard of local anesthetics? (amide or ester)
Lidocaine ; amide
• Local anesthetics and water solubility ? are they acids or bases?
Poorly water soluble
They are BASES
When mixed with Hydrochloric acid
Become water soluble
Because local anesthetics are poorly water soluble they are supplied as
Hydrochloric salts
Local anesthetics since they are supplied as hydrochloric salts become
Acidic ph 6.0
How does the fact that they are acidic affect Local anesthetics
More painful on injection
Slower onset of action (because they become ionized and only unionized can penetrate)
Benefits of Alkalization of local anesthetic solution
Makes onset of action shorter
Less pain when you inject
Some providers may add ________to alkalinized
Sodium bicarbonate
What is the Functional unit of peripheral Nerve?
Axon
Extension of Centrally located neuron
Axon
Function of schwann cells
Insulation and Support
In unmyelinated cells, one schwann cell for
multiple axons
In LARGER cells, one schwann cell cover___________ with several layers of ______ (lipid)
one axon with several layers of MYELIN
Small segment of Axon without myelin
Node of Ranvier
What does the Node of ranvier has making it able to generate impulse? how does the impulse travel? what is the term use for that?
Contains large number of Sodium channles
Impulse travel from node to node
Saltatory conduction
What is the PRIMARY area where LOCAL anesthetics EXERT THEIR ACTIONS?
Node of RANVIER
Which one is more difficult to block with local anesthetics, myelinated or unmyelinated?
MYELINATED
Myelinated fibers are _____and conducts impulses _____
larger; faster
How many nodes of ranvier must be blocked for prevention of nerve conduction?
2-3 Nodes of ranvier
Bundle of axons together is called
Fasciculi
What are the 3 layers of the Fasciculi?
Endoneurium
Perineurium
Epineurium
Role of epineurium
Act as a barrier that Local anesthetics must get through to work.
Resting membrane potential or peripheral nerve? Cause by?
-70 to -90 ; ionic imbalance as accomplished by Na-k+ ATPAse
Local anesthetics exert their effects by
Blocking the Na+ Channel
Local anesthetics have greater affinity for Na+ channels in _____and _____states. Known as the ________hypothesis (extra)
Active
Inactive
Guarded receptor
Some receptors have affinity for both the ionized and UN-ionized form of the local anesthetics? Which form can penetrate the membrane
UNIONIZED
MOA of benzocaine______only occur in the ______Form
interact with ion channel within the membrane
uncharged form
Define minimum blocking concentration (Cm)
The lowest concentration of drugs needed for blocking impulse propagation. think of it like MAC for local anesthetics
Because the ______form of the molecule crosses
the cell membrane, compounds that are more lipophilic have a _____onset of blockade
nonionized ; faster onset
Can local anesthetic bind when Na+ in resting state?
NO
The more frequently the sodium channel depolarized the
the more time for LA have to bind, the faster the drug action will be to block
Effect of : Increased nerve fiber diameter on Cm
Increase Cm
Effect of Increased myelination on Cm
Increased Cm
Greater distance between nodes of Ranvier on Cm
Increased Cm
Summary of factors that increase Cm
Increased nerve fiber diameter
Greater distance between node of ranvier
Increased myelination
Effect of “increased tissue pH” on Cm:
Decreased Cm
Effect of “ high frequency of nerve stimulator” on Cm
Decreased Cm
Effect of “ Pregnancy” on Cm
Decreased Cm
Effect of “ elevated tempature” on Cm
Decreased Cm
Summary of factors that decrease Cm
Increased tissue ph
high frequency of nerve stimulator
Pregnancy
Elevated temperature
Nerve fibers classified based on
Diameter and myelination
Conduction faster on
Wider diameter and myelination
What are 3 classes of PN fibers?
A, B, and C
What are the subtypes of PN A fibers
Alpha
Beta
Gamma
Delta
Largest fibers
A- Alpha
Fastest conduction velocity
A-Alpha (60-120m/s)
Most myelinated
A-alpha
A-ALPHA RESPONSIBLE FOR (MP)
MOTOR FUNCTION
PROPRIOCEPTION
what is the fiber last blocked by LOCAL anesthetics?
A-ALPHA
A-BETA CONDUCTION velocity is
30-70m/s
A-BETA responsible for
Touch
Pressure
A -GAMMA responsible for
Skeletal muscle tone
Reflexes
A- gamma CV
15-35 m/s
A- Delta responsible for
Pain, temperature and Touch
The fibers constitutes pre-ganglionic autonomic nerves
B fibers
Fibers that local anesthetics BLOCK FIRST
B fibers
Which are the ONLY UNMYELINATED FIBERS?
C fibers
Slowest conduction out of all fibers
C fibers (0.5 m/s)
2nd fibers to be BLOCKED is ____ along with _____Fibers
C fibers
A-delta fibers
C fibers conduct
Pain , temperature, touch and post ganglionic symp neurons
Clinically , sequence of Differential blockade is
***Autonomic function BLOCKED FIRST by B fibers
Pain, touch and Temperature by A delta and C fibers)
Motor and proprioception BLOCKED LAST by A-alpha, beta and gamma
Blocked first in differential blockade
Autonomic function
Blocked last in differential blockade
Motor and proprioception
Best example of differential blockade is
Bupivacaine
0.125 % blocks autonomic function some pain and touch BUT NOT motor and proprioception, same with 0.25%
However, 0.5% block them all
NEURONS blocking order
Blocking order
1st –> B fibers, autonomic function block
2nd –> A-delta fast pain and temp; C slow pain
3rd –> A-gamma, muscle tone and motor
4th –> A-beta, sensory touch and pressure
5th –> A-alpha, motor and , skeletal muscle
Block throbbing pain and temperature
C fibers
Para and sympathetic PREGANGLIONIC Neurons are______ but POST GANGLIONIC neurons are _____
B fibers; C fibers
Block SHARP, prickling pain and temperature
A-delta
What are the 3 characteristics segments of Local anesthetics?
Aromatic ring (lipophillic) Intermediate Carbon group (ester or amide) Tertiary amine (hydrophillic)
All local anesthetics are (acids/bases)
weak bases
***Best determinant of POTENCY for LOCAL anesthetics is
Lipid Solubility (Oil water partition is m
The more lipid soluble the agent
Onset of action determines by
the more drug enters the axon
Ionization
***The duration of action of local anesthetics is related to
PROTEIN BINDING
Linkage characterizes drugs as either
Ester or amide
How can you tell ester from amide?
Ester “one i”
amide “ two i’s)
Ester are Hydrolized by
Plasma cholinesterase (blood)
Hydrolysis of Ester results in which metabolites? and what is it associated with>
PABA ( Paraaminobenzoic acid); asscociated with allergic reactions
Amides are metabolized by
Liver
Amides allergic reaction are RARE and are due to
Methylparaben- structurally similar to PABA
Systemic toxicity ( more likely or less likely with agents)
Amide (more likely )
Ester (less likely )
Which one is chemically stable in solution
Amide
Onset of action of amide vs ester
Amide (mod to fast)
Ester (slow)
pKa of Ester compared to amide
Ester 8.5-8.9
Amide close to ph 7.4 which is 7.6 - 8.1
Distribution of local anesthetics is dependent on________and there is _________> what is a major factor?
Blood flow
High initial uptake by lung
Redistribution
Relative clinical potency and chloroprocaine; Oil/ water partition
1; 1
Relative clinical potency and Mepivacaine; Oil/ water partition
2; 1
Relative clinical potency and Lidocaine Oil/ water partition
2;4
Relative clinical potency and Tetracaine Oil/ water partition
8; 80
Relative clinical potency and BUPIVACAINE Oil/ water partition
8;30
The short duration local anesthetics are
PC
Procaine
Chloroprocaine
The Intermediation duration local anesthetics are
Mepivacaine
Lidocaine
The LONG duration of action Local anesthetics are
Tetracaine
Etidocaine
Bupivacaine
Ropivacaine
The most important determinant of onset of action is
IONIZATION
Drugs with lower pKa such as _______have SHORTER onset of action
AMIDE
Speed of onset of local anesthetics related to
pKa
Decreased tissue pH leads to
more ionized local
poorly absorbed in tissue
Pt at high risk due to decreased tissue ph are
Septic w/ metabolic acidosis
Renal failure patients
Agent with the slowest onset of action
Procaine
2 drugs with SLOW onset of ACTION
Procaine
Tetracaine
Moderate onset of action : % unionized at physiologic pH of 7.4
Bupivacaine
17%
Fastest onset of action of LA (CLEM)
Chlroprocaine
Lidocaine
Etidocaine
Mepivacaine
Lidocaine : % Unionized at physiologic pH of 7.4 ____ph is
24%; 7.7
Which drug has the HIGHEST % of Unionized at physiologic pH of 7.4?
Mepivacaine 39%
pH of 7.6
________may reduce the latency of onset and increase the duration of action of local anesthetics
• Sodium bicarbonate
Drugs that help increasing duration of action
Sodium bicarbonate
Dextran
theoretically improve the onset &
intensity of block
Carbonation
• All local anesthetics produce ________ of vascular smooth muscle except____ and___
Relaxation
Mepivacaine & Cocaine
The vasodilation caused by local anesthetics result in
Increase blood flow to the site where it is applied
reduce duration of action
INCREASED potential for systemic toxicity
Degree of systemic vasodilation from more to least?
Lidocaine > Procaine > Mepivacine (none)
Effects of SYSTEMIC TOXICITY depends on
TOTAL DOSE GIVEN
Area where local anesthetics is applied also affects
Speed and extent of systemic absorption/toxicity
***Most to least absorbed MUST KNOW WELL IvTIc CaudPaEpiBP SubaScif SuQ
Intravenous>Tracheal>Intercostal>
Caudal>Paracervical>Epidural>BrachialPlexus > Subarachnoid/Sciatic/Femoral >
Subcutaneous
Why add vasoconstrictors such as EPI to local anesthetics??
it Decrease rate of systemic absorption by increasing the concentration of the drug at the site of action resulting in more intense block and less toxicity
Epinephrine prolongs the duration of action for local infiltration, peripheral nerve block and epidural administration of 3 drugs >ProLiMe
The other ones yes but no effects on epidural
Procaine
Mepivacaine
and lidocaine.
Epinephrine proven to be the
most effective agent
Usual Concentration of Epi for lidocaine
1:200,000 or 5mcg/ml
Explain why Chrorprocaine has a 2% unionized at physiological pH but still has a fast onset of action
because HIGHER concentration administered
Plasma half time of procaine and chlorprocaine
less than 1 minute
What is the most TOXIC ester with limited clinincal use
Tetracaine
There are no_________cholinesterases meaning drug is eliminated out of the CSF by?
Spinal ; diffuse out of the CSF
Rate of hydrolysis of Ester from more to least (CPT)
Chloroprocaine > Procaine > Tetracaine
Drugs that can reduce metabolism of Ester
Succinylcholine
because it is also metabolized by plasma cholinesterase which can saturate metabolism
Toxicity unlikely with liver disease when given those 2 drugs
Procaine and Chlorprocaine
Amide are metabolized by the _______and metabolism are affected by
Liver;
Hepatic Blood flow
Hepatic enzyme activity
Amide metabolism from GREATER To least (PELMeB)
Prilocaine Etidocaine Lidocaine Mepivacaine Bupivacaine
What are the 2 MAJOR factors affecting the clearance of AMIDE local anesthetics?
HEPATIC Enzyme activity
Hepatic blood flow
For amide, clearance is independent of
Potency, lipid solubility, protein binding or chemical structure.
Sequence of local anesthetics toxicity
CircLTVS
MURCA
Which is the FIRST SIGN of Toxicity
- Circumoral numbness (mouth, lip, tongue) FIRST SIGN
- Lightheadedness
- Tinnitus
- Visual Disturbance
- Slurring of speech
- Muscle twitching
- Unconsciousness
- Grand mal seizures
- Coma
- Apnea
Lidocaine manifestations at 1-5mcg/ml
Analgesia
Lidocaine manifestations of toxicity when is there CV collapse
> 25mcg/ml
Lidocaine manifestations of toxicity when is there Coma/Apnea
15-20 mcg/ml
Lidocaine manifestations of toxicity when is there Seizures/Unconsciouness
10-15mcg/ml
MMCTS occurs with 5-10mcg/ml of lidocaine
Muscle twitching Myocardial depression CIRCUMORAL /TONGUE NUMBNESS Tinnitus Systemic Hypotension
What can be aministered to prevent the CNS toxicity of local anesthetics?
Midazolam 5-10 minutes prior to LA injection
Agents less likely to cause toxicity are (CPL)
Chloroprocaine
Prilocaine
Lidocaine
Prevention of Toxicity:
aspirate syringe before injection (watch for blood or CSF)
Inject small amount 5ml q 30-60 monitor for s/s toxicity
know expected pharmacokinetics of drugs
Continuous monitoring, blood levels may not peak for 30 minutes
Acid base disorders that increase risk for toxicity
Respiratory and metabolic acidosis
Acid base disorders that decrease risk for toxicity
Alkalosis
At 1st sign of toxicity have patient voluntarily
Hyperventilate which will decrease the transfer of agent in to the cell
CNS toxicity primary concern is
Seizures
2 types of neurological disease that can occur
Transient neurological sydnrome
Cauda equina
Associated with continous spinal catheters
CV toxicity of LA are dose dependent
- Lower concentration_____and ______and higher conentration_____and ______
Vasoconstriction, increase SVR
Vasodilation, hypotension
Electrophysiology effect of toxicity
Decrease automaticity
Prolong conduction time
Increase PR and QRS
Selectivity of LA with CARDIOTOXICITY from greatest to lowest? (BEL)
Bupivacaine
Etivacaine
Lidocaine
Cardiac toxicity associated with BEL are SEVERE AND RESISTANT, use
INTRA-LIPID THERAPY
For Bupivacaine , use
IV lipid emulsion 20%, 100 ml enough to resuscitate from bupivacaine induce arrhythmias
Methimobglobinemia what is it?
Iron oxidized from ferrous to ferric, cannot bind to or carry O2
Treatment of Methymoglobinemia
Methylene blue 1-2 mg/kg
Lidocaine onset of action
< 2min
Lidocaine DURATION of action ? Longer with ?
30-60 min; Epinephrine
Max dose of lidocaine
3mg/kg
Bupivacaine onset of action is
5-10 min
Bupivacaine Duration of action is
200min ; 540 with epi
Bupivacine MAX dose
2.5mg/kg
Mepivacaine and prilocaine onset of action is
3-5 min; 5 min
Mepivacaine and prilocaine Duraction of action is
45-90 min; 30-90min
Max dose of Mepivacaine and prilocaine
5-6 mg/kg; 5mg/kg
Procaine onset of action is
10-20 min
Procaine Duration of action is
40 min
Procaine max dose
7mg/kg
Ropivacine onset of action is
5-15 min
Ropivacaine max dose
3mg/kg
Initial intake of lidocaine in this organ_____
LUNG
Which will have faster onset of action, drugs with pka close to physiological pH or farther from physiologic pH
CLOSEST to physiological pH have a more RAPID onset of action
Which is responsible for the Neural blockade?
IONIZED
Greater vasodilation – ________systemic absorption;_______duraction of action
Increased; reduced duration of action
Localization of local anesthetic receptor relative to the cell membrane: where is the receptor localized to?
Internal membrane surface
More chances of Allergic reaction
Ester because of PABA
Minimum Blocking concentration
Lowest concentration of a drug that is needed for blocking impulse propagation
Lidocaine and bupivacaine
Low pKA
fastest onset of action
Concentration use for obstetric NOT FDA approved
0.75%
LA with EPI
Prolonged Duration of action
Decreased Toxicity
PRILOCAINE
MOST Associated with Methemoglobinemia
Chlorprocaine
Rapid onset
low potential due to RAPID HYDROLYSIS
Not recommended for spinal
Not recommended for spinal
Chlorprocaine
Procaine
First synthetic Anesthetic produce
Slow onset and low potency
Procaine
Limited use due to short duration of action
Procaine
Toxicity and slow regional onset limit this agent in application such as regional anesthesia
Tetracaine
Bupivacaine 0.75%
Not recommended for pregnant women
Bupivacaine 0.75%
Not recommended for pregnant women
prolonged asystole
Drug of choice for AMI when episodes of vfib and vtach are not easily concerted by defi and epineprhine (persistent afib and vtach)
Lidocaine
Duration of action of lidocaine
Short
May cause toxicity at high concentration
Lidocaine
Lidocaine primary metabolite is
Monoethylglyceinexylidide (use to assess hepatic functions to predict morbidity and mortality)
Intranasal lidocaine
use to assess migraine headache
Lidocaine can use to treate
Seizure
Lidocaine and sodium channels
Fast sodium channel blocker
Max dose of lidocaine without epi
4mg/kg
Total dose not to exceed 300mg
Max dose of lidocaine with epi
7mg/kg
Total dose not to exceed 500mg
Bupivacaine onset, duration and potency
onset slow
potency high
duration long
Preferred local for Obstetric_____________but IF EMERGENCY C SECTION , _______May be preferred
Bupivacaine 0.125 -0.5%; Chloroprocaine
Indications for Bupivacaine
when long acting needed
Provide sensory analgesia with less motor block
Significant advantage of bupivacaine
Longer duration
Differences amount local anesthetics agents is the duration of block is dependent on
Concentration of the anesthetic
Contraindications for bupivacaine
0.75% NOT BE USED FOR OB (Cardiac arrest, death)
NOT BE USED IN OB PARACERVICAL block due to FETAL bradycardia and death
Max single dose of BUPI without epi
175mg
Max single dose of BUPI with epi
225mg
Do not repead dose at interval less than ___hours for bupi
3 hours
Max dose of Bupi in 24 hours
400mg
If you use the 0.5% solution for bupivacaine without epineprhine used in obstetrics for continuous epidural anesthesia
Total dose should be limited to 320mg
Onset, potency and duration of Mepivacaine
Rapid onset, potency weak, duration of action intermediate
This local anesthetic is NOT FOR SPINAL DOSING . However used for?
MEPIVACAINE
Epidural and caudal
Preferable use in OB patients with hx of HTN or cardiac disease bcause long duration
Mepivacaine
Less cardiotoxicity and less adverse effects
Ropivacaine
Onset of action of ropivacaine
Moderate
Motor block is less intense than bupivacaine
Ropivacaine
Preferred for procedures where sensory block is desired but intense motor blockade is not required
Ropivacaine
Long acting lidocaine derivative
Etidocaine
Used for regional , limited epidural and not used for spinal
Etidocaine
Cardiotoxic properties similar to bupivacaine
Max dose 300mg without epi
400 with 1:200000 epi
Onset of action rapid and major drawback is methemoglobin
Prilocaine
Use in EMLA cream
Prilocaine
With Prilocaine: Methemoglobin, Due to oxidation of normal hemoglobin by the
Prilocaine hepatic derived metabolite O-Toluidine
Methomoglobin serum concentrations usually appear
8mg/kg or greater max 600mg
Chloroprocaine duration of action? onset?potency ?
short ; rapid; low
Appropriate anesthetic for OP surgery as long as it’s less than 1 hour long
Chloroprocaine
Chloroprocaine without epi
11mg/kg
Chloroprocaine with epi
14mg/kg to 1000mg
Procaine rapid
Hydrolysis –> PABA (allergic reactions )
Max single dose of Procaine
1000mg
Tetracaine use for
Opthalmic analgesia
Prolonged used for not recommended due to
Severe Keratitis
Corneal adverse effects