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Exam 2
Local Anesthesia PP
17
Veterinary Medicine
Professional
04/01/2016

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Term
What are local anesthetics used for?
Definition
-diagnostics, analgesia, motor blockade (localize source of lameness or pain)
Term
What is believed to be the mode of action for local anesthetics?
Definition
-change in membrane polarization causes sodium to enter the nerve cell and potassium to leave the cells
Term
What are the possible mechanisms for local anesthetics to block sodium influx?
Definition
-blocking the sodium channel
-causing sodium channel to remain closed
-thus signal never makes it to the brain
Term
How are nerve fibers classified?
Definition
-A: myelinated
-B: myelinated: vasoconstriction, preganglionic sympathetic
-C: nonmyelinated: slow pain, postganglionic sympathetic polymodal nociceptors
Term
What are types of A nerve fibers?
Definition
-alpha: motor
-beta: touch, pressure
-gamma: muscle spindle (proprioception)
-delta: fast pain, temperature
Term
What is the priority of nerve fiber blockade?
Definition
-sensory input
Term
What are the signs of blockade for each type of nerve fiber?
Definition
-Beta: inc skin temp, hypotension
-Adelta, C: analgesia, loss of temp sensation
-Agamma: loss of proprioception
-Abeta: loss of touch and pressure sensation
-Aalpha: loss of motor function
Term
What (and how) affects the potency of local anesthetics?
Definition
-inc potency = inc lipid solubility, dec size = inc penetration
Term
What (and how) affects the speed of onset of local anesthetics?
Definition
-inc lipid solubility = inc speed of onset
-inc pKa = dec nonionized, permeable form = dec speed of onset
-the closer the pKa is to tissue pH the more rapid the onset
Term
What (and how) affects the duration of effect of the local anesthetics?
Definition
-inc duration of effect = inc lipid solubility, protein bidning
Term
What are the two general types of local anesthetics?
Definition
-Amides and Esters
Term
What are the important characteristics of Amides and give some examples.
Definition
-most common, very stable, not hydrolyzed by cholinesterases, enzymatic degradation in the liver
-ex: Lidocaine, Mepivacaine, Bupivacaine, Prilocaine
Term
What are the important characteristics of esters? Give some examples.
Definition
-readily hydrolyzed by plasma cholinesterases
-short half-lives when stored without preservatives
-ex: cocaine, benzocaine, procaine
Term
Toxicity of local anesthetics is dependent on what conditions?
Definition
-dependent on volume, concentration, rate of absorption, rate of metabolism
Term
What are the signs of local anesthetic toxicity?
Definition
-CNS: seizures
-CVV: dysrhythmias, hypotension
-Resp: apnea
-Methemoglobinemia: benzocaine, prilocaine
-Localized or systemic allergic rxn: esters/procaine
Term
What are examples of additives that can be administered with local anesthetics and why are they given?
Definition
-Epinepherine: dec local perfusion, dec rate of vascular absorption, inc intensity, prolongs activity, tissue necrosis, prolonged blockade
-Hyaluronidase: improves diffusion, inc absorption, tixicity, dec duration
Term
What methods of administration are possbile with local anesthetics? Examples for each method?
Definition
-Local infiltration: Inverted L, intercostal nerve block
-Reigonal block: epidural, paralumbar, peterson eye block
-Topical: splach bblock, transdermal patches, EMLA cream
-Intra-articular
-CRI: lidocaine
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