Local Anesthetics Flashcards
Factors that determine LA properties:
Potency?
Duration of Action?
Speed of Onset?
Potency=lipid solubility
Duration of Action=protein binding
Speed of Onset=pKa (closer to pH=faster)
LA rate of systemic absorption (greatest to least)
IV>tracheal>intercostal>caudal>paracervical>epidural>brachial plexus>sciatic>subQ
How man mcg/ml of epinephrine in a 1:200,000 mixture?
5 mcg/ml
How man mg/ml is 2% lidocaine?
20 mg/ml
Abnormal pseudocholinesterase decreases rate of metabolism of which drugs?
Succinylcholine, mivacurium, ester LAs (except cocaine)
Which LAs can lead to methaemoglobinaemia?
What does the pulse ox read?
What is the treatment?
Benzocaine, prilocaine, and less so lidocaine
85%
Methylene blue
Receptors of LAs
alpha subunits of voltage-gate sodium channels (intracellular side)
Duration of block is not enhanced with epi for which LAs?
Bupivicaine and ropivicaine (highly protein bound)
What is the pH of pre-mixed epinephrine to LA solutions? How does this change the effect of the LA?
Acidic (pH 4-5) because epi degrades quicker in alkaline environments. Acidic solution slows block onset. (more LA in ionized or BH or conjugate acid form= less LA crossing membrane)
Which protein binds LAs and other bases?
AAG: alpha-1-acid glycoprotein (albumin carries acidic drugs like barbiturates)
Misinterpretation of LA “allergies”
- allergic reaction to PABA (metabolite of esters)
- allergic reaction to methylparaben (similar to PABA), a preservative in some amides
- epinephrine reaction
- methaemoglobinaemia from o-toluidine (metabolite of prilocaine)
1:1,000 epi is how many mg/ml?
1 mg/ml, or 1,000 mcg/ml
Liposomal bupivicaine- duration and safety compared to bupi
Longer duration and comparable safety compared to bupi
Only LA that is acidotic?
Benzocaine
- pKa 3.5
- exists in uncharged form at physiologic pH
*all other LA pKa’s are higher than 7.4, meaning that some fraction of them exists in the protonated (charged) form
How many nodes of Ranvier must be blocked to achieve anesthesia?
3
