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Local Anesthetics
LA
55
Nursing
Graduate
10/11/2015

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Cards

Term
Local Anesthetics Definition
Definition
Drug that produces reversible conduction blockade of impulses along centeral and peripheral nerve pathways
Term
History of LA
Definition

Cocaine

 

Procaine (ester)

 

Lidocaine (amide)- intense and longer acting 

Term
Differential Blockade
Definition
Autonomic--> Sensory--> Motor
Term
LA site of Action
Definition

Axon 

 

Must bind to Na Channels inside of the cell 

Term
Endonerium
Definition
Surround each individual nerve
Term
Perineurium
Definition
Surround each individual nerve fascile
Term
Epineurium
Definition
Encases groups of fasicles into a sheath
Term
Salatory Conduction
Definition

jump from one node of ranvier to another

 

Takes 2-3 Nodes for LA to take effect 

Term
Sensory Block
Definition
Temperature (Cold before hot)--> Pain--> Touch--> Deep pressure
Term
Sequence of Recovery
Definition
Motor--> Sensory--> Autonomic
Term
LA Affect on RMP and Threshold
Definition
Does NOT alter resting membrane potential or threshold potential
Term
Vascular Effects of LA
Definition

Vasoconstriction at low doses

 

Vasodilation at clinically relevant doses 

Term
Systemic Absorption
Definition

The lower the systemic absorption, the higher the safety profile

 

Dose is direct linear relationships of absorption-not drug concentration or speed of injection 

 

Highly lipid soluble have prolonged effects because they are stuck in fat 

Term
Injections to High Vascular Areas
Definition
IV > Tracheal > Intercostal > Caudal > Paracervical > Epidural > Brachial > Subarachnoid > Sciatic > Femoral > Subcutaneous
Term
Esters
Definition

Metbolized by rapid hydrolysis by psuedocholinesterases

 

Have PABA metbolites that can cause allergic reaction

 

Have one i in the name 

Term
Benzocaine
Definition

Can cause methemoglobinemia

 

No Baby-Orajel 

Term
Amides
Definition

Metabolized by CYP450 enzymes in the liver

 

Have two I in the name 

 

Prilocaine > lidocaine > Mepivicaine > Ropivicaine > Bupivicaine (rate of metabolism) 

Term
Methemoglobenemia
Definition

Caused by prilocaine, lidocaine, and benzocaine 

 

Fe3+ which cannot carry O2

 

Treatment is methylene blue 1-2mg/kg over 5m in 

Term
Cm
Definition

Minimum concentration of LA necessary to produce conduction blockade

 

Cm of motor fibers is 2x that of sensory fibers that why you have differential blockade 

Term
Conduction Blockade
Definition

LA are weak bases

 

Unionized form cross the lipid membrane and then becomes ionized

 

Ionized form binds to the intracellular sodium channel at the H gate during inactivated-closed state prevent Na+ from going through the channel and causing an action potential 

Term
Potency of LA
Definition

Directly related to Lipid solubility= more lipid soluble the more potent 

 

Closely related to protein binding= more lipid soluble the more protein bound and the longer duration of action 

Term
Potentcy is Affected by
Definition

Hydrogen, ion balance

 

Fiber size, type, and myleination

 

Vasodilation/Vasoconstrictor properties

 

Frequency of stimulation of the nerve

 

pH

 

Electrolyte concentrations (hypokalemia and hypercalcemia antagonized blockade) 

Term
Which enantiomer are safer in Racemic mixtures of LA?
Definition

S enantiomer

 

Ropivacaine and Levobupivacaine are pure S enantiomers

 

Most LA are racemic 

Term
pKa
Definition

Direct relationship to onset of LA

 

If the pKa of a LA is closer to physiologic pH then it will have a more rapid onset

 

This is because the ionized portion and unionized portion are in a closer ratio

 

Lidocaine, mepivacaine, prilocaine, and etidocaine have a pka ~7.6-7.8

 

Ropivacaine and bupivicaine have a pKa~8.1-8.6 so they have a longer onset 

Term
Exception to pKa rule of onset
Definition

Chloroprocaine

 

Has a high pKa and rapid onset


Think it might be due to the high clinical dose we use 

Term
Commerical Prepartion of LA
Definition

Poorly water soluble

 

Acidic prepartions

 

Can alkalinze the solution to make a faster onset- makes more LA available in unionzed form

 

May cause precipitation 

Term
Chemical Makeup
Definition

Weak bases

 

Aromatic ring- essentential in making the LA lipophilic

 

Tertiary amine group

 

Amide or ester connenction 

Term
Liposomal LA
Definition

LA incorporated into liposome

 

Prolongs duration and decreases toxicity

 

Slow release formulation

 

Exparel- liposomal bupivacaine 

Term
Epinephrine added to LA
Definition

Vasoconstrictor

 

Prolongs LA block by decreasing systemic absorption

 

5mcg/ml or 1:200,000

 

Should never be injected into end arteries (ears, nose, penis, fingers) 

Term
Neuroaxial Additives
Definition

Opioids and clonidine 

 

Work synergistically

 

Longer, more intense blockade

 

Clonidine can improve duration of analgesia by 2 hrs

Term
Pregancy and LAs
Definition

Beware of Ion trapping- fetal pH is usually lower than moms, unionized form crosses placenta but then gets stuck there

 

Hormonal changes dilate epidural veins so dose should be reduced by 30% reguardless of trimester 

 

Have reduced plasmaesterase- keep in mind with esters- prolonged block 

Term
Bupivacaine
Definition

3 mg/kg max dose

 

Highly lipid soluble and potent with longer duration of action

 

0.25% bupivacaine dose should be equally to how many kg pt is 

 

Ex. 10 kg pt, 10 ml is max 

Term
Lidocaine
Definition

4 mg/ kg 

 

Lidocaine with epi is 7 mg/ kg 

Term
Allergic Reactions to LAs
Definition

Usually caused by PABA metabolite of esters

 

Allergy to ester does not mean allergy to amide

 

Sometimes it's the preservatives (methylparaban) 

Term

Systemic Toxicity 

 

(LAST)

Definition

Most commonly from accidential IV injection during epidural or PNB 

 

Aspirate before you injection

 

Usually see signs immediately up to 20 mins

 

neurotoxic signs before cardiac signs 

Term
1-5 mg/kg of Lidocaine
Definition
Causes analgesia
Term
5-10 mg/kg of Lidocaine
Definition

Numbness

 

Tinnitus

 

Muscle Twitching

 

Systemic Hypotension

 

Myocardial depression

Term
10-15 mg/kg of Lidocaine
Definition

Seziures

 

Unconsciousness 

Term
15-25 mg/kg of Lidocaine
Definition

Apnea

 

Coma 

Term
> 25
Definition
Cardiovascular depression
Term
Transient Neurologic Symptoms
Definition

Moderate to Severe pain in lower back, buttocks, and posterior thighs

 

Occurs within 6-36  hr after single shot spinal

 

Recovery usually within 1-7 days 

 

Usaully from intrathecal lidocaine- NO LIDOCAINE spinals 

Term
Cauda Equina Syndrome
Definition

Diffuse injury across the lumbosacral plexus

 

Have sensory anesthesia, bowel and bladder dysfunction, and paraplegia

 

Usually lidocaine- no lidocaine spinals 

Term
Anterior Spinal Artery Syndrome
Definition

Lower extremity paresis with variable sensory deficit thats diagnosed as neural blockade resolves

 

Possibly from thrombosis or spasm of the anterior spinal artery

Term
Bupivacaine Toxicity
Definition

Precipitous hypotension, cardiac dysrhythmias, AV heart block

 

Resuscitation resistant- need fat emulsion (Intralipid)

 

LA does not have enough time to dissociate during diastole 

 

May be precipitated by beta blockers, dig, calcium channel blockers 

Term
Intralipid Dosing for Bupivacaine Toxcitity
Definition

20 % lipid emulsion

 

1.5 mL/kg over 3 mins

 

IV infusion of 15 mL/kg/hr 

Term
Nebulized Lidocaine
Definition
Can cause bronchoconstriction in asthmatics
Term
Clinical Uses for LA
Definition

Topical

 

Local Infiltration

 

Aerolized for Fiberoptic Intubation

 

Peripheral Nerve Blocks

 

IV regional (Bier Block)

 

Spinal

 

Epidural 

Term
Peripheral Nerve Blocks
Definition

Diffuse from the outer surface toward the center

 

Therfore fibers that are more proximal becomes anesthetized first then distal

Term
IV Regional
Definition

Extremity isolated from rest of the systemic circulation by tourniquet

 

Duration determined by how long tourniquet is inflated 

 

NO BUPIVACAINE 

Term
Tumescent Lidocaine
Definition

Subcutaneous infiltration of large volumes of solution with diluted lidocaine

 

Provides local anesthesia, bloodless aspirates, and postop analgesia

 

Slow release of Lidocaine into the circulation that peaks in 12-24 hours

 

High risk of mortality 

Term
Max Dose for Tumescent Lidocaine
Definition
35 mg/kg to 55 mg/kg
Term
Atypical Psuedocholinesterase
Definition

Usually genetic

 

Will have a dibucaine # < 20

 

This means that if you give them Succinylcholine they will have apean and paraylsis lasting 2 hours or longer 

Term
Dibucaine #
Definition

70 is normal

 

40-70 will have a mimimally prolonged effect

 

<20 will have apnea and paralysis for 2 hours or longer 

Term
Acquired Conditions Affecting Pseudocholinesterase
Definition

Liver Disease

 

Renal Disease

 

Malnutrition

 

Pregnancy 

 

Malignancy

 

Burns

 

Cardiopulmonary Bypass 

 

(pseudocholinesterase are synthesized in the liver) 

Term
Benzcaine Gels
Definition

Can cause methemoglobinemia

 

NO FDA warning on labels

 

Look for signs of hypoxia

 

Do not give to children under 2 years 

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