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
