LA: Intro to LA Flashcards
What is the individual axon bundled by?
Endoneurium
What does the perineurium encase?
It bundles axons into fascicles
What are the fascicles encased by?
Epineurium
What is important to note about the histology of the axon fascicles in terms of solubility?
There are a lot of fat cells so the fat solubility of the anesthetic is important
What type of neurons are A fibers?
Large and Myelinated
How many subtypes of A fibers are there?
4: Alpha, Beta, Gamma, Delta
Which A fiber type is afferent?
Delta
What type of neuron in a B fiber?
Autonomic, Preganglionic
What type of neuron is a C fiber?
Small, Unmyelinated
Autonomic post-ganglionic
Sensory for pain and temp
Rank the A, B, and C fibers in order of sensitivity to LA
A > B > C
What cell myelinates axons in the CNS?
Oligodendrocytes
What cell myelinates axons in the PNS
Schwann
During a nerve impulse propagation what is the first step?
Opening of the Sodium channels creating a depolarization
After depolarization to +40 mV what is the next step of the nerve impulse?
Sodium channels close and the K permeability increases allowing K to flow out of cell down its gradient repolarizing the cell
What is the special receptor theory of LA action?
LA acts by binding to receptor site within the sodium channel.
This prevents sodium influx and hence prevents nerve depolarization
What are the three parts of the basic LA molecular structure?
Hydrophobic Aromatic Group
Intermediate chain (ESTER or AMIDE)
Hydrophilic Amino Group
Which is the commonly used LA that is an ester?
Procaine (Novocaine)
How does pH effect the molecular structure of the LA?
All LA exist in equilibrium between a neutral and ionized form, the ion is acidic.
The balance is dependent upon the molecule’s pKa and can be calculated using the HH equation
Once the LA is injected how do its components work? (ACID VS BASE)
LA is injected as an acid, but it is the free base that is lipid soluble and does the actual work
What is the most commonly used LA in the USA and UK?
Lidocaine
Lignospan, Octocaine, Xylocaine
Is lidocaine and amide or ester?
Amide
What is the max safe dose of Lidocaine?
4.4 mg/kg
300 mg MAX
What is the max safe dose of Articaine?
7 mg/kg or 500 mg
Why might articaine result in greater penetration into the nerve?
More lipid soluble
Which LA has an extra ester linkage?
Articaine
What nerve block should be used cautiously with Articaine?
IAN
Why might Articaine have more neurotoxicity?
4% Solution
How much solution does each cartridge of LA have?
1.8 ml
Each 1% of LA is the equivalent of…?
10 mg/ml
So how much in a 1%, 2%, 3%, 4% Carpule?
1%: 18 mg/cc
2%: 36 mg
3%: 54 mg
4%: 72 mg
What does 1:100,000 mean
1 gram in 100,000 mL
What is the max safe dose of epi for a normal adult?
.20 mg
What is the max safe dose of epi for a cardiac patient?
40 micrograms
What is important to balance with cardiac patients however?
Profound nerve block is key because too much pain could cause the patient to release endogenous epi.
