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65 Cards in this Set
- Front
- Back
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Local anesthetics
Main MOA |
Blocks conduction of impulse along nerve pathway
Nonionized form crosses axon membrane to intracellular site of action -equilibrates to ionized form and the ionized form binds to inactive, closed Na+ channel Slows rate of depolarization so threshold can't be reached and no action potential occurs(doesn't alter threshold or resting potential) |
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LAs are acids or bases
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Weak bases
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Addition of NaHCO3 to LA
Limitations |
Increase non=ionized fraction = increased speed of onset and depth of blockade
Also decreases burning of injection Limited by precipitation |
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Amount of NaHCO3 to add to lido, mepiv, bupiv
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Lido/mepiv: 1 mEq / 10cc LA
Bupiv: 0.1 mEq/ 10cc bupiv |
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Structure of LAs
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Lipophilic group (usually benzene/PABA) separated by a hydrophilic group (usually tertiary amine) by an aminoAMIDE or aminoESTER link
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Na+ channel blockade is dependent on...
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Frequency dependent
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Which types of nerves are better blocked?
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Small, unmyelinated fibers
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Other MOA of LA
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Blocks voltage gated K+ channels
Evidence of G-protein coupled receptor activity |
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Sequence of blockade
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1) Sympathetic block- Autonomic blockade (sympathectomy)
2) Sensory blockade- pain and temp 3) Blocks proprioception and pressure 4) Motor blockade |
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What is a walking epidural?
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Blocking of pain and temp with absence of motor blockade using very low concentration
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A fibers- function
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Proprioception
Pain, temp, touch Small motor Muscle tone |
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B fibers- function
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Preganglionic autonomic
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C fibers- function
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Dull pain, temp, touch
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What determines LA toxicity
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Absorption into circulation (away from site of action)
Vascularity of tissue |
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EMLA
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Eutectic mix of LA- dermal analgesia
5% lidoc/5% prilocaine emulsion |
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Absorption depends on...
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Blood flow to area
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Addition of epi to LA
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Local vasoC = decreased perfusion = increased DOA
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Order of risk of CNS and cardiac toxicity of injection
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TICPEBSS
Tracheal>intercostal>caudal>paracervical>epidural >brachial plexus >sciatic> subQ |
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Distribution of LA depends on
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Organ uptake- central compartment
Tissue:blood partition coefficient |
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Metabolism of esters
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Rapid hydrolysis by plasma cholinesterase
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Esters - drugs
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Chloroprocaine
Procaine Tetracine Cocaine |
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Order of rate of metabolism of esters
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Chloro>procaine>tetracine
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Increased DOA of esters with what conditions?
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Atypical plasma cholinesterase, pregnancy, renal insufficiency
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Esters
Which drugs have active metabolites |
Procaine/benzocaine metabolized to PABA - allergen
Benzocaine-O-toluidine |
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Amides
Drugs |
Prilocaine
Lidocaine Mepivicaine Ropivicaine Bupivicaine Etidocaine |
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Amides
Metabolism |
CYP450
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Amides
Order of rate of metabolism |
Priloc>lidoc>mepivac>ropiv> bupiv
Please Leave My Ropivicaine Be |
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Amides
Drugs with active metabolites |
Prilocaine metabolized to O-toluidine
O-toluidine converts hgb to methemoglobin |
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Amides
Tx of methemoglobinemia |
Tx with methylene blue 1-2 mg/kg over 5 min
Reduces methgb to hgb |
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Signs and symptoms of methemoglobinemia
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Cyanosis, anxiety, HA, fatigue, confusion, coma, seizures, acidosis, death
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LA CNS effects
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First symptoms to show in CNS
Circumoral numbness, tongue parasthesias blurry vision Excitatory then CNS depression |
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How do you decrease risk for seizures of LA?
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Benzo, STP, propofol (increases seizure threshold)
Hyperventilate |
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Cauda equina syndrome
What causes it S/S |
Large/repeat doses of 5% lidocaine into SA space
Permanent neurologic damage of nerves of caudal equine |
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Cauda equina syndrome
Which drugs have highest risk (in order) of causing it |
Lido = tetra > bupiv >ropiv
(LiTe Bu Ro) |
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Transient neurologic symptoms
What causes it? what increases risk of getting it? |
LA into spinals
Increased risk in lithotomy position and ambulatory surgery |
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Transient neurologic symptoms
S/S |
Dysesthesia, burning, aching in lower extremities/buttocks due to radicular irritation
Usually resolves in 1 week |
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Use of lidocaine for bronchodilation
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Relaxes bronchial smooth muscle
IV lidocaine 1-1.5 mg/kg IV |
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Which LA have 1st pass pulmonary uptake?
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Lido, bupiv, prilo
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CV effects of LA
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Class I antiarrhythmics
Depresses automaticity, inotropy Autonomic inhibition- don't give to 3rd degree heart block Need really high doses to cause CV effects |
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Treatment of CV effects of LA
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ACLS, support, lipid emulsion
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Allergies caused by LA are usually due to...
Alternative to use in case of allergies |
PABA- esters have PABA derivative
Amides have methylparaben preservative Use preservative free amide |
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Mix of 2 LA have a ....
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additive effect
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Interaction of LA and nDmr
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potentiates
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Placental transfer of LA
Which drugs cross placenta? |
Amides: prilo>lido>bupiv
Fetal ion trapping occurs Esters generally rapidly hydrolyzed before it can cross |
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What dilution of epi is added to LA?
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1:200,000
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Cocaine
Class |
Ester
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Cocaine
Unique properties |
Intrinsic vasoC
Inhibits NE and other catecholamine reuptake Partial hepatic metabolism |
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Cocaine
ADR |
SNS stimulation from blocking catacholamine reuptake
Hyperpyrexia Addition of eli can sensitize myocardium to catecholamine and exaggerate cardiac stimulation |
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Chloroprocaine
Use |
Good for labor epidurals (doesn't cross placenta, rapid hydrolysis)
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Tetracaine
Unique aspect |
Slow onset, long duration
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Lidocaine
Uses-7 |
1) Local/regional anesthesia
2) Nebulized for laryngoscopy/bronchoscopy 3) VT/VF 4) Blunt SNS to intubation 5) Sedation 6) Decrease injection pain 7) Antitusive |
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Lidocaine
Metabolism |
Hepatic and 1st pass pulmonary uptake
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Bupivicaine
Metabolism |
Hepatic and 1st pass pulmonary uptake
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Bupivicaine
ADR |
Cardiac toxicity (resistant to tx) d/t binding of Na+ channels in myocardium
HypoTN, Arrhythmias, AV block R isomer is cardiotoxic |
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Levobupivicaine
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Less cardiotoxi than bupiv
L-isomer of bupiv |
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Etidocaine
Why don't we use it more |
Motor block>sensory block
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Prilocaine
Unique aspects Metabolism |
1st pass pulmonary uptake
Hepatic metabolism to o-toluidine |
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Procaine
Doses |
400 mg
600 mg w/ epi 7 mg/kg 12 mg/kg w/ epi |
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Chloroprocaine
Doses |
800 mg
1000 mg w/ epi 9 mg/kg 12 mg/kg w/ epi |
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Tetracaine
Doses |
100 mg
200 mg 2/ epi |
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Lidocaine
Doses |
300 mg
500 mg w/ epi 5 mg/kg 7 mg/kg w/ epi |
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Etidocaine
Doses |
300 mg
400 mg w/ epi 5 mg/kg |
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Mepivicaine
Doses |
300 mg
500 mg w/ epi 5 mg/kg |
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Ropivicaine
Doses |
300 mg
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Bupivicaine
Doses |
175 mg
225 mg w/ epi 2.5 mg/kg 3 mg/kg w/ epi |
