Local Anesthetics Flashcards
Benzocaine
Procaine
Cat: Short acting ester LA (benzocaine = topical, procaine = infiltrate, epidural)
MOA: Blocks activated/inactivated Na channels
Adverse: allergy to PABA, anxiety, convulsions (GABA block - tx w/diazepam), CV collapse
Cocaine
Cat: short acting ester for nose/throat
MOA: block activated/inactivated Na channels, use dependent
SE: PABA allergy, anxiety, convulsions (GABA block - tx w/ diazepam), inc HR/contraction, VFib, hypertension
Beware of drug abuse
Lidocaine
Ropivacaine
Cat: long acting amide LA
MOA: block activated and inactivated Na channels, use dependent
SE: anxiety, convulsions d/t GABA, CV collapse (bradycardia, hypotension)
Which LA has reduced affinity for cardiac sodium channels and is therefore associated with less cardiac toxicity?
S-isomer of ropivacaine
Locations of use of lidocaine vs ropivacaine
Lidocaine: infiltration, Bier block, peripheral, epidural, spinal
Ropivacaine: peripheral
Epinephrine
Reduces systemic absorp of local anesthetics via vasoconstriction via alpha 1 adrenergic activation
SE: localized tissue necrosis
Increases LA action by 50%
Clonidine
Used with LAs for epidural and spinal admin to further reduce pain transmission
MOA: prevents NT release at C and Ad fibers via presynaptic alpha 2
Diazepam
Treat convulsions d/t systemic absorption of LA into CNS by activating GABA receptors in CNS
3 characteristics that determine level of lipophilic
- # of hydrocarbon chains and length
- Length of intermediate connecting chain
- # /length of aromatic ring hydrocarbons
A delta fibers
Fast pain
Glutamate to NMDA
Neospinthalmic neurons
Myelinated
C fibers
Second pain
Substance P to P receptors
Paleospinothalmic neurons
Esters
One “i”
Short duration of action
Metab by plasma/live pseudocholinesterases
Allergies: PABA derivatives
Amides
Two Is
Longer duration of action
Metab: liver p450
Why don’t local anesthetics work well in infected tissue?
Lower pH means that the LA is more charged, leaving it unable to cross the cell membrane leading to decreased potency and longer onset time
Fiber types most susceptible to LA
Small diameter
Myelinated
Firing a lot
Exterior fibers
Topical anesthesia
ENT procedures - directly to surface
Ex. Benzocaine or cocaine
Infiltration anesthesia
Injection into skin, subcut, or mucous membrane
Ex. Procaine or lidocaine
Bier block
Regional anesthesia via injection and impeding of venous flow with a tourniquet < 1 hr
Ex. Lidocaine
Peripheral nerve block
Around nerve or plexus for regional anesthesia
Ex. Lidocaine or ropivacaine
Epidural and spinal anesthesia
Epidural doesn’t puncture dura
Spinal does puncture dura
Procaine and lidocaine
Greatest risk for system toxicity
Areas of high vascularization
Intercostal > caudal > epidural
Low: brachial plexus, sciatic nerve
Low systemic absorption of LA effects
Disruption of sensory perception
High systemic absorption of LA effects
Brain: confusion, tremor, convulsions
CV: dec contractility, bradycardia, vasodilation, hypotension
Direct injection of LA into vasculature causes…
Temporary blindness Aphasia Hemiparesis Convulsions Coma Cardiac arrest
What can help reduce cardiac and neurotoxicities from direct injection
IV lipid emulsions
