Wk 8: Local Anesthetics Flashcards
Local anesthetics are used to provide analgesia and anesthesia for various surgical and nonsurgical procedures: (4)
-Acute and chronic pain management
-Reduce perioperative stress
-Improve perioperative outcomes
-Treat dysrythmias
Local anesthetics produce _________ conduction blockade of impulses along central and peripheral nerve pathways
reversible
With progressive increases in __________ of local anesthetics, the transmission of autonomic, somatic sensory, and somatic motor impulses is interrupted
concentrations
(the larger the concentration, the more prevalent those changes become)
Local anesthetics produce:
________ nervous sytem blockade
________ anesthesia
________ muscle paralysis in the area
innervated by the affected nerve
Autonomic
Sensory
Skeletal
(knowing purpose of block will guide choice of type and concentration of drug)
In almost all instances, _____ or an _____ bond links the hydrocarbon chain to the lipophilic aromatic ring
Ester (-CO-)
Amid (-NHC-)
The connecting _________ chain is the basis for classifying as ester or amid local anesthetics
Hydrocarbon
The important differences between ester and amide local anesthetics relate to:
________
________
Metabolism
Potential to produce allergic
reactions
Procaine
Chloroprocaine
Tetracaine
Esters
“No one likes one I’d Ester”
Lidocaine
Prilocaine
Mepivacaine
Bupivacaine
Levobupivacaine
Ropivacaine
Amides
(2 I’s)
Only amide local anesthetic with rapid onset
Lidocaine
Only ester local anesthetic with rapid onset
chloroprocaine
Drugs such as __________, __________, and ___________ have been incorporated into liposomes
Lidocaine
Tetracaine
Bupivacaine
Liposomal local anesthetics ________ duration of action and _______ toxicity
Prolong
Decrease
Hemorrhoidectomy, bunionectomy, field blocks, brachial plexus blocks, etc.
Liposomal local anesthetics can prolong duration of action up to ____ hours
72
Local anesthetics prevent transmission of nerve impulses (conduction blockade) by inhibiting passage of _____ _____ through ion-selective ______ ______ in nerve membranes
sodium ions
sodium channels
Local anesthetics inhibit passage of sodium ions through ion-selective sodium channels in nerve membranes
This _____ the rate of depolarization, therefore _______ ________ is not reached and an _________ ________ is not propagated
Slows
threshold potential
action potential
_______________ of local anesthetic necessary to produce conduction blockade of nerve impulses
Comparable to the MAC for inhaled anesthetics
Minimum effective concentration (Cm)
(a means to compare local anesthetic potencies)
Each local anesthetic has a unique minimum effective concentration (Cm), reflecting differing ______ of each drug
potencies
The minimum effective concentration (Cm) of motor fibers is approximately ______ that of sensory fibers
Therefore, sensory anesthesia may not always be accompanied by skeletal muscle ________
twice
paralysis
(need higher concentration of LA to block motor fibers compared to sensory fibers)
Despite an unchanged minimum effective concentration (Cm), _____ local anesthetic is needed for subarachnoid (spinal) anesthesia than for epidural anesthesia, reflecting greater access of local anesthetics to unprotected nerves in the subarachnoid space
less
Changes during pregnancy
_______ sensitivity may be present during pregnancy
_______ _____ onset of conduction blockade
Increased
More rapid
Is there clinically significant transplacental transfer of LA between mother and fetus?
Yes
_____ in the fetus, could occur during prolonged labor, this in theory results in accumulation of local anesthetic molecules in the fetus ( ____ _______)
Acidosis
Ion trapping
Local anesthetics are _____ _____ that have pK values somewhat _______ physiologic pH
Weak bases
above
Local anesthetics with pKs nearest to ______ pH have the most _____ onset of action, reflecting the presence of an optimal ratio of _______ to ______ drug fraction
physiologic
rapid
ionized
nonionized
________ _______ activity will also influence apparent potency and duration of action
Intrinsic vasodilator
Enhanced __________ action of lidocaine compared with mepivacaine results in the ________ systemic absorption and _______ duration of action of lidocaine
vasodilator
greater
shorter
Attempts to slow systemic absorption, and thus increaser DOA include mixing ________ or _______ with LA = combats vasodilation
epinephrine
phenylephrine
Absorption of a LA from its site of injection into the systemic circulation is influenced by: (4)
Site of injection
(certain areas have higher
perfusion)
Dosage
Use of epinephrine
Pharmacologic characteristics
of the drug
Does the intercostal area of sciatic femoral area have a higher serum level?
Intercostal
Highly perfused = picked up much faster into systemic circulation
The ______ water solubility of local anesthetics usually limits renal excretion of unchanged drug to less than ____ %
Exception is cocaine, of which ___ % to ____ % of unchanged drug can be recovered in urine
poor
5%
10-12%
Water-soluble metabolites of local anesthetics, such as ______ __________ ____ ( ______ ) resulting from metabolism of ester local anesthetics, are readily excreted in urine
para-aminobenzoic acid (PABA)
Amide local anesthetics undergo varying rates of metabolism by ________ _______ located primarily in the ______
microsomal enzymes
liver
Amides
_______ undergoes the most rapid metabolism
Prilocaine
Amides
_______ and _______ are intermediate metabolisms
Lidocaine and mepivacaine
Amides
__________ and __________ undergo the slowest metabolism
Bupivacaine and ropivacaine
Compared with that of ester local anesthetics, the metabolism of amide local anesthetics is more ______ and _______
complex and slower
(amides have potential to last longer than esters)
_______ metabolism means that sustained increases of the plasma concentrations of amide local anesthetics, and therefore systemic ________, are more likely than with ester local anesthetics
Slower
toxicity
__________ drug effects of amide local anesthetics are more likely than with ester local anesthetics
Cumulative
(especially if re-dosing or giving multiple boluses)
Ester local anesthetics undergo _______ by ____________ enzyme principally in the _______
hydrolysis
cholinesterase
plasma
Esters
_________ is the most rapidly metabolized
Chloroprocaine
Esters
___________ is intermediately metabolized
Procaine
Esters
__________ is the slowest metabolized
Tetracaine
Esters
The resulting metabolites are pharmacologically ________, although para-aminobenzoic acid may be an _______ responsible for subsequent _______ _______-
inactive
antigen
allergic reactions
Allergic reactions to local anesthetics are ______ despite the frequent use of these drugs
Estimated that < ____ % of all adverse reactions to local anesthetics are due to an allergic mechanism
rare
<1%
Esters of local anesthetics that produce metabolites related to _____ - __________ _____ are more likely than amide local anesthetics to evoke an allergic reaction
para-aminobenzoic acid
_____ ________ _______ ______ (_____) is due to an excess plasma concentration of the drug
Local anesthetic systemic toxicity (LAST)
LAST
Accidental direct ________ _______ of local anesthetic solutions during performance of peripheral nerve block anesthesia or epidural anesthesia is the most common reason for excess plasma concentrations of local anesthetic
intravascular injection
Dose dependent effect of lidocaine
1-5 mcg lidocaine
Analgesia
Dose dependent effect of lidocaine
5-10mcg lidocaine
Circumoral numbness
Tinnitus
Skeletal muscle twitching
Systemic hypotension
Dose dependent effect of lidocaine
10-15mcg lidocaine
Seizures
Unconsciousness
Dose dependent effect of lidocaine
15-25mcg lidocaine
Apnea
Coma
Dose dependent effect of lidocaine
> 25mcg lidocaine
Cardiovascular depression
Treatment of LAST-induced seizures includes: (3)
Ventilation
Benzodiazepine to suppress
LAST-induced seizures
Early use of lipid emulsion
(Intralipid)
Treatment of LAST, lipid emulsion administration
Initial bolus 1.5ml/kg 20% emulsion
followed by
0.25ml/kg per minute of infusion for at least 10 minutes after circulatory stability is attained
Rare life-threatening complication that causes oxidation of hemoglobin
Methemoglobinemia
Methemoglobinemia
Rare life-threatening complication (decreased oxygen-carrying capacity) that causes _________ of hemoglobin to methemoglobin more rapidly than methemoglobin is _______ to hemoglobin
oxidation
reduced
2 local anesthetics that Methemoglobinemia have been implicated in
Prilocaine
Benzocaine
Treatment of Methemoglobinemia
Reversed with methylene blue, 1-2mg/kg IV over 5 minutes
total dose should not exceed 7-8 mg/kg
Regional anesthesia is classified according to the 6 sites of placement of local anesthetic solution
Topical or surface anesthesia
Local infiltration
Peripheral nerve block
IV regional anesthesia (Bier block)
Epidural anesthesia
Spinal (subarachnoid) anesthesia
Why isn’t cocaine used as often anymore?
Cardiovascular events d/t vasoconstricting properties
Nebulized _________ can produce surface anesthesia of the upper and lower respiratory tract before fiberoptic laryngoscopy and/or bronchoscopy
lidocaine
Lidocaine can be used for patients experiencing intractable ________
coughing
____________ or extravascular placement of local anesthetic in the area to be anesthetized by:
_____________
_____________
Local infiltration
Lidocaine
Bupivacaine
Epinephrine-containing solutions should not be injected into tissues supplied by ____ -________
______, ______, _____, and _______
end-arteries
fingers, toes, ears, and nose
(so we don’t cut off supply to end arterioles)
________ ______ ______ _______ is achieved by injection of local anesthetic solutions into tissues surrounding individual peripheral nerves or nerve plexuses such as the brachial plexus
Peripheral nerve block anesthesia
Duration of peripheral nerve block anesthesia depends on the (4)
Dose of local anesthetic
Lipid solubility
Degree of protein binding
Use of vasoconstrictor
The duration of action is prolonged more safely by _________ than by increasing the dose of local anesthetic, which also increases the likelihood of _______ ________
epinephrine
systemic toxicity
Intravenous Regional Anesthesia is also known as
Bier Block
Bier block
The IV injection of local anesthetic solution into an extremity isolated from the rest of the systemic circulation by a _________ produces _____ onset of anesthesia and skeletal muscle ________
tourniquet
rapid
relaxation
Bier block
_____ and _____ local anesthetics produce satisfactory effects when used for IV regional anesthesia
ester and amide
Bier block
_________ is the most frequently selected amid local anesthetic
Lidocaine
(Usually Lidocaine 0.5%, 50 ml)
Epidural anesthesia
Local anesthetic solutions placed in the ________ or _______ ______ space produce epidural anesthesia
epidural
sacral caudal
Epidural anesthesia
Local anesthetic ________ across the ______ to act on ________ and the spinal cord
sites of action is the _________
diffuses
dura
nerve roots
nerve roots
Epidural anesthesia
The slow diffusion process accounts for the ___ to ____ minute delay in onset of the sensory anesthesia after placement of local anesthetic solutions in the epidural space
15 to 30
Spinal anesthesia
Local anesthetic solutions placed into ________ CSF act on superficial layers of the spinal cord
The primary site of action is the __________ __________ as they leave the spinal cord in the _______ _______
lumbar
preganglionic fibers as they leave the spinal cord in the anterior rami
Spinal anesthesia
Dosages of local anesthetics used for spinal anesthesia vary according to the: (3)
Height of the patient (determines
volume of the subarachnoid
space)
Segmental level of anesthesia
desired
Duration of anesthesia desired
Spinal anesthesia
The _____ _____ of local anesthetic administered for spinal anesthesia is more important than the ________ of drug or _______ of the solution injected
total dose
concentration
volume
__________, __________ ,_________, and _________ are local anesthetics most likely to be administered for spinal anesthesia
Bupivacaine, ropivacaine, mepivacaine, and chloroprocaine
How do we know how much to give?
_______ and ________ are dependent on location and purpose
-IV induction
-Spinal
-Epidural
-Nerve block
Volume and concentration
Generally speaking, ______ concentrations given for analgesia
_________ concentrations given for anesthesia
smaller
higher
Alkalinization of local anesthetics
solutions
_______ the onset of neural blockade
________ the depth of sensory and motor blockade
________ the spread of epidural blockade
shortens
enhances
increases
Alkalinization of local anesthetics
Adding ____________ will speed onset of peripheral nerve block and epidural block by ____ to ____ minutes
sodium bicarbonate
3 to 5 minutes
The duration of action of a local anesthetic is proportional to the time the drug is in contact with ________
nerve fibers
_________ [ __ : _________ or __mcg/ml] added to local anesthetic solutions produces vasoconstriction
Epinephrine [1:200,0000 or 5mcg/ml]
Epinephrine limits _______ absorption and maintains drug concentrations in the vicinity of _________ to be anesthetized
systemic
nerve fibers
Decreased systemic absorption of local anesthetic due to __________ decreases the possibility of systemic __________
vasoconstriction
toxicity
(i.e. adding epinephrine)
Tumescent liposuction
The “tumescent” technique for liposuction is carried out via the ___________ infiltration of large volumes ( ___ or more liters) of solution containing highly diluted lidocaine ( ___ % to ____ %) with epinephrine ( __ : ________)
subcutaneous
5
0.05% to 0.10%
1:100,000
Tumescent liposuction
Slow and sustained release of lidocaine into the circulation is associated with plasma concentrations less than ____mcg/ml that peak ____ to ____ hours after injection and then decline gradually over the next ___ to ___ hours
1.5mcg/ml
12 to 14
6 to 14
Tumescent liposuction
Causes of death may include lidocaine ______ or local anesthetic-induced depression of cardiac _____ and ________
toxicity
conduction
contractility
Tumescent liposuction
Overall complication rate in a nationwide quality improvement study was ____% in which _____% were minor complications and ____ % were major complications
0.7%
0.57%
0.14%
Tumescent liposuction
When highly diluted lidocaine solutions are administered for tumescent liposuction, the dose of lidocaine may range from ____ to _____ mg/kg (“mega-dose lidocaine”)
35-55 mg/kg
Dibucaine is an ______ local anesthetic known for its ability to inhibit activity of normal ________________
amide
butyrylcholinesterase (plasmacholinesterase)
Dibucaine inhibits plasma cholinesterase by more than ____ % compared with only approximately ____% inhibition of the activity of atypical enzyme
70%
20%
Laboratory evaluation of patients suspected of having atypical pseudocholinesterase is facilitated by measurement of the degree of enzyme _____ by ________, a test termed the __________ _______
suppression
dibucaine
dibucaine number
Normal dibucaine number = ____
(normal pseudocholinesterase)
Low dibucaine #= ____
(atypical pseudocholinesterase)
80
20
