Quiz 4 Local Anesthetics Flashcards
Where do local anesthetics (LA) have a better access to the axon on myelinated nerves?
at the Nodes of Ranvier
What channels do LA work on to block signals on a nerve axon?
Na+ channels
Local anesthetics are greatly facilitated if the drug is in the ____________ or _________ state
Uncharged or non-ionized state
What is a quick way of telling whether the LA is an amide or ester anesthetic?
The Amides have 2 “i” in the name, ex. Lidocaine, Ropivacaine….
What correlates well with the LA’s potency?
Lipid solubility
What are some factors that affect the minimum blocking concentration of a LA?
- Fiber size
- fiber type
- myelination
- pH of tissues
- pKa of LA
T/F - a LA with a pKa closer to physiologic pH will have a higher concentration of IONZED form and can readily pass through the nerve cell membrane.
False - non-ionized
Why do LA’s with higher lipid solubility have greater potency?
they are less likely to be cleared by blood flow
Which Amides have the highest and lowest potency?
Highest - Bupivacaine (duration 200+ min)
Lowest - Mepivacaine (duration 45-90 min)
Which Ester has the highest potency?
Tetracaine (duration 200+ min)
What are 2 factors that will help determine the sensitivity of the nerve to a LA?
- Axonal Diameter: Small > Large
2. Myelination: Unmyelinated > myelinated
In spinal nerves, which is most sensitive to local anesthetics: Autonomic, sensory, or motor?
Autonomic is most sensitive.
Autonomic > Sensory > Motor
Systemic absorption of LA depends on what?
- blood flow to area being injected
- vasoconstrictors
- specific LA agent (high or low lipid solubility)
Which LA is the only one to not produce relaxation of vascular smooth muscle?
Cocaine - causes vasoconstriction which makes it great for nosebleeds and ENT procedures
If most LA’s cause relaxation of vascular smooth muscle, what could happen to your anesthetic?
- increased absorption
- decreased duration of action
- increased probability of systemic/toxic effects
How are Esters metabolized?
By pseuodcholinesterase, water soluble metabolites excreted through urine
Which 2 esters are metabolized by PABA and associated with allergic reactions?
Procaine and benzocaine
How are Amides metabolized?
P-450 and metabolism is slower than with Esters but are excreted through urine, also.
**Decrease in liver fxn will reduce metabolism and increase toxicity”
What are 2 LA’s that are implicated for causing methemoglobinemia?
Prilocaine - amide
Benzocaine spray - ester
++Treat with methylene blue
T/F: The slower a local anesthetic is absorbed into the vascular space, the less likely that high blood levels and subsequent CNS or cardiac toxicity will occur.
True
If you have 1% lidocaine, what is the concentration of that drug? (g/ml)
1 gram per 100 ml
What environments will cause ion trapping and what will it do to anesthetics?
- Acidosis, injection into acidotic/infected tissues, septic pts
- causes higher accumulation of drug, which will prolong duration of action
Effects of LA on CNS?
Effects of LA on cardiovascular?
CNS - convulsions - increased O2 consumption in presence of compromised ventilation
Cardiovascular - depresses automaticity, reduced refractory period, depressed contractility/conduction, vasodilation,
Bradycardia -> heart block -> hypotension -> cardiac arrest
How long do you need to leave EMLA cream on to get satisfactory analgesia?
1 hr covered in occlusive dressing
What sites are good for topical anesthesia?
Mucus Membranes: nose, mouth, tracheobronchial tree, esophagus, GU tract
**absorption of LA through Mucus Membranes is significant and can cause systemic toxicity
What sites should you NOT use epinephrine in your LA’s?
Should NOT be injected around end arteries like:
- fingers/toes
- Ears/Nose
- Genitals
What are concentrations of LA used for infiltration?
Lidocaine -
Procaine -
Bupivacaine -
Lido - 0.5 - 1%
Pro - 0.5 - 1%
Bupiv - 0.125 - 0.25%
What is Transient Neuologic Symptoms (TNS)?
dyesthesia, burning pain, and aching in lower extremities/buttocks associated with use of lidocaine in spinal
Methemoglobinemia becomes an issue in patient’s with severe ________ or ________ failure.
anemia, heart
