Local Anesthetics Flashcards
(97 cards)
1
Q
local anesthetic uses (general) (2)
A
surgical anesthesia, pain management
2
Q
peripheral nerve anatomy
A
axolemma (Na/K pump placement), axoplasm (ICF?), Schwann cells
3
Q
schwann cells in unmyelinated smaller nerves
A
single schwann cells cover several axons
4
Q
schwann cells in myelinated bigger nerves
A
in larger nerves, the schwann cell covers only one axon and has several concentric layers of myelin
5
Q
how many successive nodes do you need to block for LA to work
A
3 successive nodes of ranvier
6
Q
fasciculi
A
bundles of axons
7
Q
3 layers of connective tissue that cover fasciculi
A
endoneurium, perineurium, epineurium
8
Q
endoneurium
A
thin, delicate collagen that embeds axon in the fascicle. will cause a nerve injury if you inject into this.
ex) nerve emerging from C5
9
Q
perineurium
A
layers of flattened cells that binds groups of fascicles together
ex) nerve from C5 meeting nerve from C6
10
Q
epineurium
A
surrounds perineurium and is composed of connective tissue that holds fascicles together to form peripheral nerve. “holds all bundles together”
11
Q
Na/K pump in/out ratio?
A
3 Na out, 2 K in
12
Q
at which mV is Na at its inactive state
A
+20mV
13
Q
LA MOA general
A
bind to Na channel when in open or inactive states. to lesser extent, also blocks K, Ca, GPCR’s.
(do NOT alter RMP or threshold potential)
diffusion of unionized base across nerve sheath and membrane, re equilibrium between base and cationic forms in axoplasm (joins with H+), binding of cation to receptor inside sodium channel, resulting in inhibition of conduction.
14
Q
use dependent of phasic block
A
resting nerve is less sensitive to LA than one being repeatedly stimulated
15
Q
sensitivity of nerves to LA, small v large
A
small diameter and lack of myelin enhance sensitivity while larger nerves conduct impulses faster and are harder to block
16
Q
cascade of blocked fibers in order
A
preganglionic blocked with low concentrations
small C and A fibers blocked next (loss of pain and temp)
LA’s preferentially bind to smaller/unmyelinated nerves
17
Q
first sign of LA working
A
vasodilation
18
Q
can touch and proprioception still be present
A
yes, and pain from surgical stimulation can be absent still in this scenario
19
Q
Type A alpha fiber function, diameter, myelination, block onset
A
proprioception, motor.
6-22 micrometers
heavily myelinated
last for block onset
20
Q
Type A beta fiber function, diameter, myelination, block onset
A
touch, pressure
6-22 micrometers
heavily myelinated
intermediate block onset
21
Q
Type A gamma fiber function, diameter, myelination, block onset
A
muscle tone
3-6 micrometers
heavily myelinated
intermediate block onset
22
Q
Type A delta fiber function, diameter, myelination, block onset
A
pain, cold, temperature, touch
1-5 micrometers
heavily myelinated
intermediate block onset
23
Q
Type B fiber function, diameter, myelination, block onset
A
preganglionic autonomic vasomotor
<3 micrometers
light myelination
early block onset
24
Q
Type C sympathetic fiber function, diameter, myelination, block onset
A
postganglionic vasomotor
.3-1.3 micrometers
no myelination
early block onset
25
Type C dorsal root fiber function, diameter, myelination, block onset
pain, warm, cold temperature, touch
.4-1.2 micrometers
no myelination
early block onset
26
chemical structure of LA's
aromatic ring for lipophilicity
tertiary amine (hydrophilic portion of molecule)
either ester or amide linkage binds aromatic ring to carbon group
27
ester LA's (5)
```
procaine
chlorprocaine
tetracaine
cocaine
benzocaine
```
28
amide LA's (6)
```
lidocaine
mepivicaine
prilocaine
bupivicaine
ropivicaine
articaine
```
29
ester metabolism, allergy, DOA, longest acting ester
catalyzed by plasma and tissue cholinesterase via hydrolysis, rapid
if you're allergic to 1 ester, you're allergic to all. greater chance of ester allergy than amide because of PABA but still a very small chance
shorter acting due to ready metabolism
longest acting ester is tetracaine
30
amide metabolism, allergy, DOA, protein binding
metabolism by the liver
last longer for that reason
effect of drug stops when it leaves that part of the body, which is different than it stopping when drug is metabolized
allergy super rare
longer acting because more lipophilic and protein bound. require transport to the liver for metabolism
31
Cm
minimum concentration of LA necessary to produce conduction blockade of a nerve impulse. analogous with MAC for inhaled anesthetics
Cm of motor fibers is approximately twice that of sensory fibers. sensory anesthesia may not always be accompanied by paralysis.
32
relationship between absorption of LA, toxicity, and termination of action
systemic absorption results in termination
| the slower the LA is absorbed, the less likely there will be toxicity
33
relationship between concentration of LA and onset
the higher the concentration injected, the faster the onset
34
lipid solubility correlates with
increased binding
increased potency
longer duration of action
tendency for severe cardiac toxicity
35
LA bind to (2 proteins)
alpha 1 acid glycoprotein, albumin to a lesser extent
36
what plays a major role in duration of action for LA's
injection site
37
PKa and LA
LA's are bases that become more ionized when placed in a solution with a pH less than pKa. drugs with pKa closer to physiological pH have faster onset
(chlorprocaine is the exception)
38
tetracaine pKa, % ionized at physiologic pH, % protein binding, onset, DOA
```
8.5
93
94
slow
180-600m
(use this for a spinal if you run out of bupivicaine. some patients get movement back but they feel numb sometimes still)
```
39
lidocaine pKa, % ionized at physiologic pH, % protein binding, onset, DOA
```
7.9
76
64
fast
90-120m
faster onset and less protein binding so used faster/shorter DOA
```
40
bupivicaine pKa, % ionized at physiologic pH, % protein binding, onset, DOA
```
8.1
83
95
slow
180-600
slower onset, more protein binding, longer DOA, more ionized
```
41
which drugs won't vasodilate to the extent of bupivicaine
lidocaine, ropivicaine
42
what are the implications of relaxation/vasodilation
decreases DOA, increases plasma concentration and potential toxicity because greater vasodilation means increased absorption
43
total dose of LA determines ________ not _______ or _________
plasma level
| volume or concentration
44
uptake of LA's based on regional anesthesia, highest to lowest blood concentrations
```
IV
tracheal
caudal
paracervical
epidural
brachial
sciatic
subcutaneous
```
45
additives to decrease the rate of absorption
```
epinephrine
sodium bicarbonate
clonidine
dexmedetomidine
opioids
ketorolac
dexamethasone
hyaluronidase
```
46
epinephrine for LA
increased duration and potency of block
decreases risk of systemic toxicity
does not prolong block for all LA to same extent
"the shorter acting the drug, the greater the effect you will see with epinephrine"
47
which drugs are prolonged with epinephrine for local infiltration, peripheral nerve block, and epidural
lidocaine
mepivicaine
procaine
48
which drugs are prolonged DOA for epinephrine with peripheral nerve block but not epidural
prilocaine and bupivicaine
49
sodium bicarbonate use, MOA, limitation
used in obstetrics with epidural anesthesia
theoretically raises pH of LA solution resulting in more drug in ionized state
may result in less pain on injection
major limitation is precipitation that can occur
50
distribution of amide or ester LA
distribution of these are similar
decrease in plasma concentration to highly perfused tissue, based on redistribution
secondary distribution to rest of body, muscle receives most
51
metabolism of esterases considerations
catalyze hydrolysis of ester LA
procaine and chlorprocaine have plasma half life less than 1 minute
atypical plasma cholinesterase can increase possible toxicity
52
metabolism of amide LA consideratoins
occurs in liver cia CYP 450
severe hepatic disease can prolong metabolism of this disease
also, consider if they have less protein ex) elderly
53
renal dysfunction consideration
while renal dysfunction will affect clearance far less than hepatic failure, it will affect the protein binding to both A1AG and albumin
54
LAST
local anesthetic systemic toxicity
55
LAST most common reason/pathophys
inadvertent intravascular injection. initial blocking of inhibitory neurons thought to cause seizures. blocking of cardiac ion channels results in bradycardia, vfib most serious complication.
56
LAST subjective symptoms
tinnitus and metallic taste first, then
agitation, circumoral numbness, blurred vision
muscle twitching, unconsciousness, seizures
very high levels: cardiac and respiratory arrest
57
LAST most common in which procedures (3)
epidural (puncture vein or dura)
axillary
inter scalene (close to carotid and IJ, this block goes in C7)
58
LAST prevention strategies
test dosing
incremental injection with aspiration
use of pharmacologic markers
ultrasound
59
LAST treatment
```
airway management
seizure suppression (benzos, succ)
prevent hypoxia and acidosis
lipid emulsion therapy
epinephrine <1mg/kg
```
AVOID prop and vasopressin
60
lipid emulsion dosing
Greater than 70kg
bolus 100mL of 20% over 2-3min
infusion of 200-250ml over 15-20min
Less than 70kg
1.5ml/kg lipid emulsion 20% over 2-3min
.25ml/kg/min IBW
can re bolus to a dosing limit of 12ml/kg
61
LAST lipid emulsion therapy MOA
1. capture local anesthetic in blood (lipid sink, decreases potency of LA)
2. increased fatty acid uptake by mitochondria
3. interference of Na+ channel binding
4. promotion of calcium entry
5. accelerated shunting
62
lidocaine max dose, max dose with epi
4mg/kg
| 7mg/kg
63
mepivicaine max dose, max dose with epi
4mg/kg
| 7mg/kg
64
bupivicaine max dose, max dose with epi
3mg/kg
| NA
65
ropivicaine max dose, max dose with epi
3mg/kg
| NA
66
procaine max dose, max dose with epi
12mg/kg
| NA
67
Chloroprocaine max dose, max dose with epi
11mg/kg
| 14mg/kg
68
Prilocaine max dose, max dose with epi
7mg/kg
| 8.5mg/kg
69
Tetracaine max dose, max dose with epi
3mg/kg
| NA
70
what are amide related allergies more commonly associated with
preservatives
| ex) paraben, methylparabel, metabisulfite
71
Methemoglobinemia MOA, drugs, tx
ferris form of HGB (Fe2+) converted to ferric HGB (Fe3+)
Benzocaine Induced involves infants <2y/o
Prilocaine induced is related to metabolites ortho toluidine
tx methylene blue 1-2mg/kg over 3-10min (transient decrease in SpO2)
high levels may require transfusion or HD
72
Prilocaine dosing, contraindications
dosing should not exceed 2.5mg/kg
| avoid in children under 6, pregnant women, patients taking other oxidizing drugs
73
Cauda Equina Syndrome and risk factors
bowel and bladder dysfunction with LE weakness and sensory impairment related to spinal cord ischemia. risk factors include supernormal doses of LAS or maldistribution of LA within intrathecal space
74
Transient Neurologic Symptom (TNS)
associated with intrathecal lidocaine, presents as burning, aching, cramp like pain in low back and radiating down thighs for up to 5 days postop. other risk factors include lithotomy position and outpatient surgery
75
Lidocaine pKa, duration of action, protein binding, metabolism
pKa slightly above physiologic pH, fair amount of nonionized drug
rapid onset but DOA decreased
protein binding 64-70%
metabolism: liver
76
Lidocaine Solutions Available (7)
```
.5%
1%
1.5% with epi 1:100,000
1.5% with epi 1:200,000 (labor epidural test dose)
2%
4%
5%
```
77
Lidocaine uses (6)
```
antiarrhythmic
topical
induction
nebulized
multimodal pain management
regional anesthetic
```
78
ACLS algorithm: lidocaine
```
depresses myocardial automaticity
class 1B
dose for VT/VF:
1-1.5mg/kg IV/IO
.5-.75mg/kg (refractory)
3mg/kg (total)
maintenance infusion: 1-4mg/min (30-50mcg/kg/min)
```
79
EMLA acronym, mixture, contraindications
Eutetic Mixture of Local Anesthetics
1:1 lidocaine: prilocaine, mixture
contraindicated in mucous membranes, broken skin, infants <1mo, methemoglobinemia hx
80
Reasons Lidocaine is Given During Induction
decrease pain of propofol, attenuate CV response to intubation, attenuate ICP increase in patients with decreased compliance
81
Most significant interventions to avoid pain of propofol
```
AC vein (bigger vein)
veno occlusion (lido 20mg in 10ml with tourniquet)
small dose of opioids
```
82
Lidocaine and attenuation of SNS dosage and positive effects
1.5mg/kg IV 1-3min prior to laryngoscopy attenuates HTN and rise in ICP
2mg/kg completely attenuates cough given 1-5min prior to intubation
83
Lidocaine and Topical usage
decrease of emergence phenomenon (cough, sore throat, dysphoria)
LTA
lido jelly
filling ETT cuff with jelly (takes 60min, low dose alkalized lido 40mg shown more effective)
(do be aware that additives to lido spray can cause sore throat and hoarseness)
84
technique for filling ETT with lido jelly
add 2ml lido, 1-2ml NaHCO3-, then saline to match cuff volume
85
airway block and lidocaine
4% nebulized lido right into oropharynx
| or 4% lido injected right into cricothyroid membrane for transtracheal block, if pt coughs it spreads which is good
86
lidocaine infusions MOA and dosage
multimodal pain management, goal is to use alot less narcotic. usually given in conjunction with mag intraop
1.5mg/kg bolus dose then 2mg/kg/h infusion
87
Lido infusion MOA, uses related to pain, considerations of infusion
relatively unknown. may involve Na channels, may involve blocking the priming of polymorphonuclear granulocytes
not beneficial for all surgical procedures
shown to reduce postop pain and speed up return of bowel function in open and lap procedures
decrease pain improve functional outcomes in prostatectomy, thoracic and spine procedures
not uncommon to need CV support
88
Bier Block type of block, indications, dosage, surgical uses
peripheral nerve block, IV regional anesthesia. indicated for short procedures
25-50ml of .5% lido
onset time 5-10 min
tourniquet pain at 20 minutes
in venous system
done for surgeries that are minimally invasive like carpal tunnel
89
dose dependent effects of lidocaine: plasma concentration of 1-5mcg/ml and its effect
analgesia
90
dose dependent effects of lidocaine: plasma concentration of 5-10mcg/ml and its effect
```
circumoral numbness
tinnitis
skeletal muscle twitching
systemic hypotension
myocardial depression
```
91
dose dependent effects of lidocaine: plasma concentration of 10-15mcg/ml and its effect
seizures
| unconsciousness
92
dose dependent effects of lidocaine: plasma concentration of 15-25mcg/ml and its effect
apnea
| coma
93
dose dependent effects of lidocaine: plasma concentration of >25mcg/ml and its effect
CV depression
94
Exparel drug, where its injected, DOA
bupivicaine combined with liposomal agent DepoFoam that encapsulates it in honeycomb like structure of numerous aqueous chambers. lipid membrane separate each other.
injected directly into surgical site
provides reduced opioid requirements for up to 72h
95
Exparel dose, uses, mixing with other drugs, administration considerations, adverse effects
dose based on surgical site and volume required to cover the area. do not exceed 266mg (20ml, 1.3% of undiluted drug).
can be administered either undiluted or diluted up to .89mg/ml (1:14 dilution by volume) with preservative free sterile saline
approved for peripheral nerve blocks in brachial plexus, not approved for all nerve blocks yet
surgeons will use bupivicaine and exparil, remember they'll need to be bridged to exparil. cannot mix with anything but bupivicaine (lido will break down liposome)
for single dose admin only, administer with 25g or larger bore needly, inject slowly via infiltration into surgical sit e with frequent aspiration to minimize risk of intravascular injection. do not administer if product discolored or if vial has been frozen or exposed to high temperature for an extended period of time. invert vial multiple times to re suspend particles immediately prior to withdrawing drug from vial. use diluted suspensions within 4 hours of preparation in a syringe
>10% can get nausea and vomiting
96
exparel should not be used for
obstetrical paracervical blockade
patients <18 years old
epidural or intrathecal anesthesia
97
Cocaine
original LA derived from cocoa plant, only one that is naturally occurring.
has ability to block monoamine transporter in adrenergic system. blocking reuptake of catecholamines results in significant vasoconstriction and sympathetic stimulation.
used primarily for topical anesthsesia of the nose and throat. max dose 5ml in 5% solution
should be used with caution with other epinephrine containing solutions (MAOI's, TCA's- r/t catecholamines)
