Local Anesthetics Flashcards
local anesthetics
reversibly block the propagation of electrical impulses along nerves
effect of local anesthetics on nerve conduction physiology
prevent stimuli from reaching the threshold, NOT lowering the resting state
Main MOA of local anesthetics?
block voltage-gated sodium channels
Order of the Differential Blockade
- Vasodilation
- Loss of sensation of temperature
- Loss of sharp pain
- Loss of feeling of light touch
- Loss of motor activity
Why does the differential blockade occur the way that it does?
dependent on type of nerve fiber - less or non-myelinated axons will be the first susceptible to anesthetic
Critical Length
anesthetic must block 3 OR MORE NODES OF RANVIER to stop the impulse from propagating (otherwise it could jump and continue down the nerve)
3 Parts of the Chemical Structure of a Local Anesthetic
- lipophilic benzene ring
- intermediate chain (ester or amide)
- hydrophilic amine group
What intermediate chain do we see more of - esters or amides?
amides (they are metabolized by the liver)
4 Main Properties Influencing Local Anesthetic Activity
- Molecular Weight
- pKa (MOST IMPORTANT)
- Lipid Solubility
- Degree of protein binding
pKa effect on speed of onset
higher pKa = slower onset
physiologic pH
7.4
pKa of local anesthetic and physiologic pH
the pKa which is closer to physiologic pH will have a faster onset
effect of lipid solubility on speed of onset
higher lipid solubility = delayed onset (there’s fat in lots of places in the body so it will go there instead)
effect of protein binding on duration of action
higher protein binding will INCREASE the duration of action
What drug is pharmacologically active - free or bound?
free
Nocita
encapsulated bupivacaine to slow release
Do local anesthetics work in inflammation?
no, because the pH is so low (6.0)
order of absorption of local anesthetics
brachial plexus - sciatic/femoral - intercostal - epidural
- Intercostals (HIGHLY VASCULAR)
- Epidural
- Brachial Plexus
- Sciatic/Femoral
True or False: Local anesthetics are the only analgesics that stop transduction or transmission of nociception.
TRUE
Adverse effects of local anesthetics are mainly caused by?
HUMAN ERROR (inadvertent IV injection or too high of a dose)
What two systems will be adversely affected if a local anesthetic is overdosed?
- CNS (at two times the safe dose)
- Cardiovascular (at ten times the safe dose, and can be fatal)
Best treatment if overdosed?
IV lipid emulsion (aka le bacon) and SUPPORTIVE CARE
Lidocaine
most versatile, intermediate acting, MAC sparing
can be given IV
Mepivacaine
similar to lidocaine, lasts a little longer, more commonly used in our horses
Bupivicaine
slow onset, long acting, highly cardiotoxic; good for differential blockade
Short Acting Ester Local Anesthetic?
procaine (won’t really see used clinically)
3 Common Uses of Local Anesthetics
- Peripheral Nerve Blocks (dentistry, ortho, incisional blocks)
- Epidural (tail amps, C-sections)
- Topical (IV catheter placement)
