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27 Cards in this Set
- Front
- Back
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motor fibers
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A-alpha
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propioception fibers
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A-beta
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muscle tone
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A-gamma
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pain touch
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A-delta
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autonomic function (preganglionic)
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B (white ramus & contain myelin sheath hence have faster conduction speeds than post ganglionic fibers)
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autonomic function) postganglionic
Afferent sensory nerve (pain and temperature) |
C
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mechanism of local anesthetics
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interfere with voltage gated sodium channels (reversibly intracellular portion)
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what two factors affect the nerve blockade
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concentration and volume
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sequential blockade....
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-Small fibers fibers (C) are more susceptible than large fibers (A)
-Myelinated (B) fibers are more susceptible than non-myelinated (C) fibers - Autonomic (C,B) -->Sensory(C, A-delta) --> Motor (A-alpha) - B --> C,A-delta --> A-alpha - Temp (cold ->hot) --> pain--> touch --> deep pressure --> propioception |
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local anesthetics
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-benzene --ester/amide (linkage) --amine
-ester linkage --> broken by plasma cholinesterase -aminoamides --> metabolized by liver - B+ (H+) <--> BH+ - by adding more Bicarbonate it will increase the ration of lipid soluble form/ cationic form facilitating drug entry |
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what is the only local anesthetic with vasoconstrictive properties
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cocaine (4% used in clinically )
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purpose of epi added to local anesthetic solution
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- increases the intensity and decreases the systemic absorption prolonging the block
- decrease the intraneural clearance and redistribution of local anesthetic - increases the safety margin |
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Name Ester local anesthetics
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chloroprocaine
procaine tetracaine |
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what factors can increase CNS toxicity
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-decrease protein binding (alpha-1-glycoprotein bind basic)
-acidosis -vasoconstriction -hyperdynamic circulation |
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what factors decrease CNS toxicity
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-barbiturate
-benzodiazepines -decreased systemic absorption (epi) |
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max dose of LA (esters)
1. benzocaine 2. chloroprocaine 3. cocaine 4. procaine 5. tetracaine |
1. N/A
2. 12 mg/kg 3. 3mg/kg 4. 12 mg/kg 5. 3 mg/kg |
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max dose of LA (amides)
1. bupivacaine (marcaine) 2. lidocaine (xylocaine) 3. mepivicaine 4. prilocaine 5. ropivicaine (naropin) |
1. 3 mg/kg
2. 4.5mg/kg (7 with epi) 3. 4.5 mg/kg (7 with epi) 4. 8 mg/kg 5. 3 mg/kg |
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why is ropivicaine and levo-bupivacaine safer?
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reduced potential for cardiotoxicity b/c of reduced affinity for brain and myocardial tissue
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cardiovascular toxicity
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hypotension
bradycardio arterial hypoxemia |
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Local anesthetics block the cardiac conduction system through dose dependent block of sodium channels
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All LA especially Bupivicaine b/c of its stronger affinity to resting and inactiviated sodium channels
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Local Anesthetics bind to Sodium Channels ....
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Bupivacaine dissociates so slowly that the duration of diastole at heart rates between 60 and 180 bpm does not allow enough time for complete recovery of sodium channels (so bupivacaine conduction block increases)
- bind during systole and dissociate diastole |
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treatment of systemic toxicity
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- best method (prevention - aspiration and 3ml test dose)
- treatment is supportive -administratin of lipid to the theoretically remove LA from sites of action |
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lipid emulsion
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- 20% therapy
- bolus 1.5ml/kg over 1 minute - continuous infusion .25ml/kg/min (continue for 10min till cardiac stability attained) - repeat boluse once or twice for persistatn cardiovascular collapse - max dose 10ml/kg |
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treatment of systemic toxcity
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stop injection of local
supplemental o2 support ventilation insert ETT suppress seizure (thiopental versed propofol) treat ventricular arrythmias (electrical cardioversion, vasopressin, epi, amiodarone, 20%lipid solution to remove bupivicaine) |
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TNS after a spinal anesthesia
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Transient Neurological Symptoms
- pain or sensory abnormalities lower back and extremeties -increased risk with lidocaine, lithotomy position, and ambulatory anesthesia - not associated baricity of solution |
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Local Anesthetics Allergies
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increased allergenic potential with ester local anesthetics may be caused by metabolism to paraaminobenzoic acid (which is known antigen)
PABA Preservatives: methylparaben & metabisulfate can provide an allergic response (amides contain methylparaben) |
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prilocaine and benzocaine
side effects! |
methemoglobinemia
- remember it oxidizes the iron to Fe3+ - remember it reduces its ability to bind with oxygen - remember it increases the affinity with bound oxygen in other 3 heme groups - ultimately reducing its ability to release o2 to tissues (left shift curve) - > 10% met-hgb --> shortness of breath, cyanosis, mental status change, headache, fatigue, dizziness, loss of conciousness -> 50% met- hgb --> dysrhthmias, seizures, coma and death --> treat with methylene blue (1-2mg/kg) |
