Term
| What are local anesthetics used for? |
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Definition
| -diagnostics, analgesia, motor blockade (localize source of lameness or pain) |
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Term
| What is believed to be the mode of action for local anesthetics? |
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Definition
| -change in membrane polarization causes sodium to enter the nerve cell and potassium to leave the cells |
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Term
| What are the possible mechanisms for local anesthetics to block sodium influx? |
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Definition
-blocking the sodium channel
-causing sodium channel to remain closed
-thus signal never makes it to the brain |
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Term
| How are nerve fibers classified? |
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Definition
-A: myelinated
-B: myelinated: vasoconstriction, preganglionic sympathetic
-C: nonmyelinated: slow pain, postganglionic sympathetic polymodal nociceptors |
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Term
| What are types of A nerve fibers? |
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Definition
-alpha: motor
-beta: touch, pressure
-gamma: muscle spindle (proprioception)
-delta: fast pain, temperature |
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Term
| What is the priority of nerve fiber blockade? |
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Definition
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Term
| What are the signs of blockade for each type of nerve fiber? |
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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 |
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Term
| What (and how) affects the potency of local anesthetics? |
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Definition
| -inc potency = inc lipid solubility, dec size = inc penetration |
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Term
| What (and how) affects the speed of onset of local anesthetics? |
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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 |
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Term
| What (and how) affects the duration of effect of the local anesthetics? |
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Definition
| -inc duration of effect = inc lipid solubility, protein bidning |
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Term
| What are the two general types of local anesthetics? |
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Definition
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Term
| What are the important characteristics of Amides and give some examples. |
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Definition
-most common, very stable, not hydrolyzed by cholinesterases, enzymatic degradation in the liver
-ex: Lidocaine, Mepivacaine, Bupivacaine, Prilocaine |
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Term
| What are the important characteristics of esters? Give some examples. |
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Definition
-readily hydrolyzed by plasma cholinesterases
-short half-lives when stored without preservatives
-ex: cocaine, benzocaine, procaine |
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Term
| Toxicity of local anesthetics is dependent on what conditions? |
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Definition
| -dependent on volume, concentration, rate of absorption, rate of metabolism |
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Term
| What are the signs of local anesthetic toxicity? |
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Definition
-CNS: seizures
-CVV: dysrhythmias, hypotension
-Resp: apnea
-Methemoglobinemia: benzocaine, prilocaine
-Localized or systemic allergic rxn: esters/procaine |
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Term
| What are examples of additives that can be administered with local anesthetics and why are they given? |
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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 |
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Term
| What methods of administration are possbile with local anesthetics? Examples for each method? |
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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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