Week 6 Review of Local Anesthetics Flashcards
T/F: Local anesthetics can produce a reversible conduction blockade of impulses along the central and peripheral nerve pathways.
True
When and what was the 1st local anesthetic?
- Cocaine
- 1884
When and what was the 1st synthetic local ester?
- Procaine
- 1905
When and what was the 1st local amide?
-lidocaince
1943
What separates the lipophilic and hydrophilic portion of the chemical structure?
-hydrocarbon
which makes it a amide or ester
What part of the chemical structure makes the drug lipophilic active?
-Benzene Ring
What is the chemical chain for a ester?
-CO
What is the chemical chain for a amide?
-NHC
T/F: The quaternary amine is hydrophilic.
TRUE
What is the pH extracellular (usually)?
7.4
What is the pH intracellular (usually)?
7.0
What type of enantiomers does racemic use?
-s enantiomers and r enantiomers
T/F: A pure isomers uses both enantiomers s and r.
FALSE
What two drugs are pure isomers and what enantiomer do they use?
- Ropivacaine
- Levobupivacaine
- Enantiomers s
What is the benefit of a S enantiomer?
- Less nuero toxic
- Less cardio toxic
What is the mechanism of action for a local anesthetic?
-INHIBITS Na IONS PASSAGE THROUGH ION-SELECTIVE Na CHANNELS
- Slows rate of depolarization
- Threshold potential not reached
- No action potential propogated
What does a local anesthetic NOT alter?
- Resting membrane potential
- Threshold potential
What does the alpha Na+ channel subunit do?
Allows ion conduction and binds local
T/F: Local anesthetic bind to receptors in inactivated or open states.
True
What occurs if local is not permeable to the Na+?
The threshold and action potential cannot be obtained.
Is local anesthetic a strong or weak bond?
Weak
The local anesthetic binds both to the internal and external Na+ channel: which is the to be more important?
Internal channel
How does frequency dependent blockade work for local anesthetics?
- Access only obtained when receptor is in activated open state
- Nerves with more activity means faster blockade
- More frequent firing means more opportunity for access
What is minimum concentration?
minimum concentration to produce conduction blockade
What factors influence minimum concentration?
INCREASES
-Nerve diameter
DECREASES
- Higher frequency
- Higher pH
About how much more blockade is required for a motor blockade then a sensory blockade?
2 times as much
How many nodes of Ranvier must a local anesthetic block to obtain local anesthetic?
2 to 3
Which nerve fibers are preganglionic sympathetic efferent?
B fiber
Which nerve fibers are responsible for pain, temperature, and touch?
- C fibers
- A fibers
List the blockade order in which sensation will be last first?
ATP - TP - MVP
A - utonomic
T - Temperature
P - Pain
T - touch
P - Pressure
M - otor
V - ibration
P - Proprioception
A differential blockade will NOT B fibers, C fiber, and small medium A fibers.
FALSE
What nerve fiber will most likely not be blocked?
Large A Fibers
What will a differential blockade achieve?
- sympathectomy
- Loss of sensation for pain and temp
- May still have proprioception and moter.
What is the pH on a weak base local anesthetic?
7.6 to 8.9
Which form (ionized/unionized) crosses the lipid bylayer?
-unionized
What local will have a faster onsent?
-locals with pH nearest physiologic pH
Adding bicarb to a local will cause what to happen with the onset?
Faster onset by 3 to 5 minutes
T/F: The lower the pH of a local anesthetic the less it will sting.
FALSE
List the area of the body where 1st, 2nd, and 3rd distribution occur.
1st - Lungs
2nd - Heart, brain, kidney (high perfused tissue)
3rd - Muscle and fat (Low distrubution)
Which class of local is more widely distributed?
-AMIDES
Why do we worry about which vasopressor can cause fetal acidosis>
-Once the unionized local crosses the placental it become ionized do to the baby’s lower pH and can not transport.
What does lipid solubility mean?
The more lipid soluble means easier to cross lipid bylayer (POTENCY)
Amides are metabolized where mainly.
- mainly in the hepatic system
- Minimal renal exretion
Name to local amides from fastest to slow onset?
- prilocaine (FASTEST)
- Lidocaine and mepivicaine (Intermediate)
Etidocaine, Bupicaine, Popivacan (SLOW)
Where are ester metabolized and how?
- Plasma
- Cholinesterases found in the plasma through rapid hydrolysis
What one esters is not metabolized by cholinesterases?
Cocaine
What metabolite do ester make that are the main concern?
-Paraaminobenzoi acid (PABA)
What common local infection site contains little to no cholinesterase enzyme?
CSF
What factors will inhibit plasma cholinesterase?
- Deficiency
- Liver disease
- Increase BUN
- Parturients
- Chemotherapy
Which vasoconstrictor not an ester or amine can be added to a local?
- Epinephrine
- phenylephrine
- norepinephrine
Calculate the the mcg/mL if Epinephrine were labeled 1:200000.
5 mcg/cc
By how much can a vasoconstrictor prolong an effect?
1/3 time longer
Which two local anesthetic contain no vasodilator activity?
- Cocaine
- Ropiviaine
How much can clonidine prolong the effects of an epidural or a spinal?
Epidural from 1.8 hour to 5.3 hours
Spinal from 170 minutes to 215
What does epi do to lidocaines pH when mixed?
Causes the pH to go down to 4.5
T/F: Mixing locals together has a synergistic effect.
FALSE (Additive)
Which local may cause more of an allergic reaction
Esters.
If a local is injected intravascularly what are the symptoms?
- Hypotension
- syncope
- tachycardia
List Hadzic’s Progression from least to greatest.
- vertigo
- Tinnitus
- Ominous feelings
- Circumoral numbeness
- Garrulousness
- Tremors
- myoclonic jerks
- Convulsions
- Coma
- Cardiovascular collaspe
List the systemic levels related to blood flow of tissue from fastest to slowest for a local?
- IV
- Tracheal
- Intercostal
- Caudal
- Paracervical
- Epidural
- Brachial Plexus
- Subarachnoid
- Subcutaneous
Acronym: In Time I can Please Everyone But Suzi and Sally.
List important information about Transient Neurologic Symptoms (TNS)?
-Moderate to severe pain
Lower back, buttocks, and posterior thighs
-Unknown etiology
-Highest risk after intrathecal lidocaine
List important information about Cauda Equina Syndrome?
-Diffuse injury across lumbosacral plexus
Various degrees of sensory anesthesia
Bowel and bladder sphincter dysfunction
Paraplegia
-Related to Lidocaine
List important information about Anterior Spinal Artery Syndrome?
-Lower extremity paresis and variable sensory defecit.
What must the Bupivacaine levels be to see cardiotoxicity?
- 8 to 10 mcg/mL
How would you treat local anesthetic toxicity?
- Airway management
- Seizure suppression
- Management of arrhythmias
- Lipid emulsion (20%)
What drugs would be avoided for local toxicity especially if you had arrythmias.
- vasopressin
- calcium channel blocker
- Betablockers
- local anesthetic
Methemoglobinemia is related to local, but how would it be treated?
-methylene blue 1 to 2 mg/kg over 5 minutes
What is the correct dosage for a lipid emulsion (20%) therapy?
- 1.5 mL/kg (LEAN BODY MASS)
- 0.25 ml/kg
How long after would you continue to treat for a local cardiogenic toxicity?
10 minutes
