Flashcards in EXAM #3: LOCAL ANESTHESIA Deck (39):
What are the types of local anesthesia?
2) Perineural Infiltration
3) Nerve Block
4) Spinal Block
5) Epidural block
What is the difference between a spinal block and an epidural block?
Spinal= injection into subarachnoid space
- More reliable
Epidural= injection into the extradural space
- Less reliable
- More reversible
Outline the path of a pain signal to the brain.
2) Sensory afferent
3) Dorsal horn
4) Spinothalamic tract
5) Somatosensory cortex
What is the result of blocking Na+ channels on primary sensory afferents?
Inhibition of firing i.e. less pain signals going to the brain
What is the difference between protonated and non-protonated LAs?
- Non-protonated (LA) are more lipophilic
- Protonated (LAH+) binds to the Na+ receptor and inhibits it
What are the three sites of action on a Na+ channel?
1) Extracellular side of receptor
2) Intracellular side of receptor*
3) Embed in the lipid bilayer and disrupt the geometry of receptor--impedes function*
****Most drugs do a combination of these two*****
What are the two broad categories of local anesthetics?
What two portions of amides and esters are conserved?
What is the difference between amides and esters?
Intermediate chain of the chemical structure
What is the mnemonic for telling the difference between amides and esters?
Amides= 2x "i"
Esters= 1x "i"
Generally, is the important clinical difference between the amides and esters?
Amides= longer half-life/ duration of action
Esters= short half-life/ duration of action
Why is there a difference in metabolism between amides and esters?
- Amides are metabolized in the liver
- Vs. esters that are metabolized in the blood
What enzyme metabolizes esters?
What is Cm?
Minimum anesthetic concentration: minimum concentration for a standard block
What is the relationship between fiber size and Cm?
Bigger fiber= bigger Cm
List the order in which nerve fibers will be blocked.
What is the effect of pH on Cm?
Increased pH= decreased Cm
What is the effect of Ca++ on Cm?
Increased Ca++ = Increased Cm
What is the effect of vasoconstrictors in local anesthesia?
Reduction in local blood flow will:
1) Increase duration of action
2) Reduce systemic absorption
What drug is used as a common vasoconstrictor in local anesthesia?
What areas should NOT be injected with epi as a vasoconstrictor in local anesthesia?
What is the most important factor that will affect the reversal of local anesthesia?
Absorption into general circulation
What enzyme metabolizes amides?
How will the half life of an amide change in a patient with liver disease?
Increased half-life/ duration of action
What is an important clinical factor to remember about Esters and allergies?
- The inactive metabolite of esters is "PABA"
- PABA is prone to allergic reaction
Is there cross-reactivity between amides and esters in terms of allergic reactions?
No, if allergic to one you can give the other
Which class of local anesthetics are less prone to systemic toxicity?
Esters b/c they are metabolized in the blood
Which local anesthetic is associated with systemic toxicity/ cardiac toxicity that leads to complete cardiac collapse and death?
What is the treatment for LAST or Local Anesthetic Toxicity?
IV lipid emulsion that functions as a "lipid sink" to absorb lipophilic toxin
List the amides.
List the esters.
What local anesthetic can be given topically and injected?
What is the reference standard for local anesthesia?
What drug is used most often as a spinal anesthetic for epidural infusion/ post-op pain?
What is Articaine indicated for?
Analgesia in dentistry
What is cocaine indicated for?
Topical anesthesia for ENT procedures
What is the clinical use of Benzocaine?
This drug has enhanced lipid solubility and is used as a topical anesthetic
What is the clinical indication for Chloroprocaine?
Epidural agent for labor
- Lower risk of systemic toxicity
- Lower risk for fetal exposure