Local Anesthetics Flashcards
1
Q
What is the resting potential of a neuron?
A
Negative 60-70
2
Q
What does Na-K ATPase pump do?
A
Pumps 3 Na ions out for every 2 K, maintaining a negative intracellular environment
3
Q
What ion are neurons leaky to?
A
Potassium
4
Q
What ion does depolarization of a neuron ?
A
Voltage gated sodium channels
5
Q
Where do local anesthetics bind?
A
The alpha subunit preventing activation and thus sodium influx
6
Q
What happens as more local anesthetic is used?
A
The sodium channel becomes unable to conduct sodium ions and the threshold for propagation goes up
7
Q
Why is a local anesthetic block termed “use dependent”?
A
Because the local anesthetics have a higher affinity for open or inactivated channels so the fraction of Na channels with bound local anesthetic increased with frequent depolarization
8
Q
What other receptors may local anesthetics block?
A
Calcium
Potassium
Trpv
9
Q
Which has a higher sensitivity to the local anesthetic- smaller or larger diameter axons?
A
Smaller
10
Q
Which has a higher sensitivity to the local anesthetic- myelinated or unmyelinated axons?
A
Myelinated
11
Q
What is the order of sensitivity of the neurons?
A
Autonomic > sensory > motor
12
Q
Which neurons are unmyelinated?
A
C dorsal root (pain, temperature) and C sympathetic fibers
13
Q
What is the structure of local anesthetics?
A
Aromatic benzene ring and a tertiary amine bound by an ester or amide
14
Q
Are local anesthetics weak acids or weak bases?
A
Weak bases with a positive charge at the tertiary amine are physiologic ph
15
Q
What does potency of a local anesthetic correlate with?
A
Octanol solubility
Increased by adding alkyl groups
16
Q
What does acidity due to a block?
A
Antagonism
17
Q
What does hypokalemia do to a block?
A
Antagonism
18
Q
What does hypercalcemia due to a block?
A
Antagonism
19
Q
What is pka?
A
The pKa is the ph at which the fraction of ionized and nonionized drug is equal
20
Q
What form of local anesthetic will have a more rapid onset?
A
Nonionized because it permeates the epineurium more rapidly
21
Q
Which form more avidly binds the Na channel?
A
The charged cation
22
Q
What are the commercial forms of local anesthetics?
A
Hydrochloride salts with ph of 6-7
23
Q
Why are solutions with epinephrine more acidic (ph 4-5)
A
Because epinephrine is unstable in alkaline environment
24
Q
What does addition of sodium bicarbonate cause?
A
Speeds the onset of block and improves the quality due to more free base availability
25
What does duration of action depend on?
Lipid solubility and potency
26
What has a longer duration of action - lipid soluble or insoluble?
Soluble because they diffuse more slowly from the lipid rich environment to the aqueous bloodstream
27
What binds local anesthetics in the blood?
Alpha 1- acid glycoprotein
28
Which sites of injection absorb the fastest?
Tracheal > intercostal > paracervical> epidural > brachial plexus > sciatic > subcutaneous
29
Which organs are responsible for initial uptake of local anesthetic?
Brain, lung, liver, kidney, heart because these are the highly perfused organs
30
What is the alpha stage?
The initial uptake
31
What is the beta stage?
The slower redistribution to moderately perfused tissues (muscle, gut)
32
What tissue provides the greatest reservoir for distribution of local?
Muscle
33
How are esters metabolized?
By pseudocholinesterase then metabolites are excreted in the urine
34
What do procaine and benzocaine get metabolized to?
PABA - can cause anaphylaxis
35
What lacks esterases?
CSF
36
How do intrathecal blocks get terminated?
By redistribution into the bloodstream
37
What are the ester local anesthetics?
Cocaine
Procaine
Benzocaine
Tetracaine
38
How are amides metabolized?
By P459
39
Which amides are metabolized fastest?
Prilocaine > lidocaine> mepivacaine > ropivacaine > bupivacaine
40
What will decrease the metabolism of amides?
Cirrhosis
| Decreased liver blood flow: CHF, H2 blockers, Bb
41
What does prilocaine cause?
Methemoglobinemia because it is metabolized to o-toluidine
42
What other local anesthetic causes methemoglobinemia
Benzocaine
43
How do you treat methemoglobinemia
1-2 mg/kg of methylene blue of 1% solution over 5 minutes
44
Are the toxic effects of local anesthetics additive or synergistic?
Additive
45
Why is local anesthetic toxicity of the CNS excitatory?
Because they preferentially block inhibitory pathways
46
What does hyperventilating do to the seizure threshold?
Raises it
47
How much Propofol is needed to break a seizure?
0.5-2 mg/ kg
48
How much does infused lidocaine decrease the MAC by?
40%
49
What do IV lidocaine due to the cerebral blood flow?
Decreases it
50
Why don't we use lidocaine in spinal anesthesia?
Side effects of dysesthesia, burning pain and aching in butt and LE
Direct neurotoxicity
51
What is the max dose of lidocaine?
4.5 mg/kg
| 7 mg/kg with Epi
52
What is this max dose of mepivacaine?
4.5 mg/kg
| 7 mg/kg with Epi
53
What is the max dose of ropivacaine
3 mg/kg
54
What is the max dose of bupivacaine
3 mg/kg
55
What does lidocaine due to hypoxemic drive?
Depresses it through the medullary respiratory center
56
What is apnea due to in a high spinal?
Hypotension
57
What does lidocaine due bronchial smooth muscle?
Relaxes it
58
What do local anesthetics do to the heart?
```
Depresses automaticity
Depresses contractility and conduction
Arterial vasodilation (high doses)
Inhibit nitric oxide causing vasoconstriction (low doses)
```
59
What happens first CNS or cardiac signs of toxicity
CNS
60
At low doses, what is th effect of local anesthetics on the CV system?
Inhibition of nitric oxide and therefore vasoconstriction
61
What does IV administration off bupivacaine produce?
Severe left ventricular depression, Vt, AV block, VF
62
What are the CV effects of cocaine?
Decreases uptake or norepinephrine so HTN, ventricular ectopic, vasoconstriction
63
What can bupivacaine intoxication be treated with?
1.5 ml/kg lipid solution
64
Which you of locals are more likely to illicit an allergic response?
Esters
65
What are the heme effects of local?
Decreases platelet aggregation and thrombosis
| Increases fibrinolysis
66
What are the musculoskeletal effects of locals?
Myotoxic
| Worse with steroids or Epi
67
What do local anesthetics due to nondepolarizing blocks.
Potentiation them
68
What kind of local is dibucaine?
Amide
69
What drugs prolong local anesthetics?
Clonidine
Opioid
Organophosphates
Anti-acetylcholinesterase
70
How does an action potential in a neuron get terminated?
Inactivation of voltage gated sodium channels
| Potassium efflux
71
What is EMLA cream?
Local anesthetic applied transdermally to provide anesthesia for the skin
72
What does EMLA cause?
Methemoglobinemia secondary to prilocaine in the formulation
73
What deficiency should EMLA cream not be used in?
G6PD deficiency
74
What other drugs cause methemoglobinemia
```
Benzocaine
Prilocaine
Quinine
Sulfa
Dapsone
Choral hydrate
```
75
How long should EMLA cream be applied for to get the desired effect?
1 hour under an occlusive dressing
76
How long does anesthesia from EMLA cream last after removal?
1-2 hours
77
What is 20% benzocaine used for?
Mucosa
78
What is 4% cocaine used for?
Awake intubation so
| Sinus surgery
79
What is 11.8% TAC used for?
Wound repair
80
What is LET and what is it used for?
Lidocaine + Epi + tetracaine
Laceration repair
81
Which local anesthetic cross the placenta the least?
Chloroprocaine because it is rapidly metabolized by plasma cholinesterase
82
How does fetal ph affect local anesthetic concentration
Fetal ph is lower than mom's so you will get ion trapping and more concentration of local anesthetic in the fetus
83
What is the plasma half life of chloroprocaine?
12 seconds
84
What is the onset of action of chloroprocaine
6-10 minutes
85
What is the duration of action of chloroprocaine
30-60 minutes
86
What is the disadvantage of chloroprocaine?
Antagonistic effects on opioids and other locals
| Neurotoxicity
87
What are the first signs of lidocaine toxicity?
Numbness/tingling of lips
88
What are the second set of signs of lidocaine toxicity?
Tinnitus
89
What are the third set of signs?
Dizziness, lightheadedness, twitching,seizure
90
What is intrathecal lidocaine known to cause?
Cauda equina syndrome due to demyelination from pooling in this area
91
What are the risk factors of transient neurologic syndrome?
```
Lidocaine use
Lithotomy position
Early ambulation after surgery
Needle trauma
Same day surgery
```
92
What is transient neurologic syndrome?
Pain in legs, butt that develops within 24 hours of lidocaine spinal. Resolves spontaneously in 1-3 days
93
What is a Bier block?
It is IV local anesthetic used with 2 tourniquettes: a distal and proximal. The extremity is exsanguinated with an Esmarch bandage and then proximal cuff inflated. If the patient experience pain, the distal cuff is inflated and proximal deflated.
It lasts up to 90 minutes
94
How does a Bier block work?
Tourniquettes cause ischemia which provides some anesthesia and analgesia
Local diffuses into the vaso nervora and extravascularly to cutaneous branches in the skin
95
What determines the spread of spinal anesthesia?
Baricity of the drug, drug concentration, patient position
96
What does not determine the spread of spinal anesthesia?
Drug volume
97
What is baricity?
The density of a drug compared to the specific gravity of CSF
98
How is a solution made hyperbaric?
Adding glucose
99
How is a solution made hypobaric?
By adding water
100
How is a solution made isobaric?
By mixing 1:1 with CSF
101
What does drug volume affect in spinal anesthesia?
The level of blockade
102
When can a neuraxial catheter be removed with BID dosing of heparin?
Anytime
103
When can a neuraxial catheter be removed if a patient is on a heparin drip?
2-4 hours after the drip is stopped
104
When can an epidural be placed in someone taking Lovenox (1 mg/kg bid), Dalteparin, or Tinzaparin?
24 hours later
105
When can you restart lovenox after placing a catheter?
2 hours after
106
What happens when you mix sodium bicarb with ropivacaine or bupivacaine?
Precipitation and therefore decreased effectiveness and drug availability
107
Why is sodium bicarb added to local anesthetics?
It increases the ph of the solution to increase the amount of nonionized drug thereby increasing the onset time.
It also decreases pain on injection
108
What is post spinal back ache?
Happens within 7 days of spinal. Will go away on its own.
| Treated conservatively with APAP
109
Which regional block has the highest blood levels of local after blocking?
Intercostal
| Then caudal, epidural, brachial, IV, lower extremity
110
What is the adductor canal block?
Block of the femoral nerve under the sartorius to provide anesthesia to medial aspect of lower leg and distal femur
111
How much bupivacaine can you give with Epi?
2.5 mg/kg, not to exceed 225 mg
112
How much chloroprocaine can you give?
11 mg/kg
113
How much chloroprocaine with Epi can you give?
14 mg/kg
114
What's the duration of action of lidocaine?
30-60 minutes
115
What's the duration of action of lidocaine with Epi?
120-360 minutes
116
What's the duration of bupivacaine?
120-140 minutes
117
What's the duration of mepivacaine?
45-90 minutes
118
What's the max dose of mepivacaine?
7 mg/kg
119
What determines potency?
Lipid solubility
120
What determines onset?
Pka/ph
121
What determines duration of action?
```
Protein binding
(Highly - remain bound for longer so last longer)
```
122
What does BICEPSS stand for?
```
The order of site that absorbs the most local anesthetic
b- blood (IV)
I- intercostal
c- caudal
E- epidural
P- plexus (brachial)
S- sciatic
S- subq
```
123
Which nerves are affected first?
Small, myelinated fibers (B fibers)
Autonomic> sensory> motor
124
What do A-delta and C fibers feel?
Pain and temperature
125
What do A-beta fibers feel?
Touch
126
What are B fibers?
Preganglionic sympathetic nerve fibers
127
What are the most resistant fibers to local?
C fibers
128
Why is bupivacaine more cardio toxic?
It has higher affinity for resting and inactivated sodium channels in the myocardium
129
How do you treat LAST?
Intra lipid bolus of 1.5 mg/kg
Then infusion of 0.25 ml/kg/min (increase to 0.5 if persistent hypotension)
Get CPB team, avoid vasopressin CCBs and BBs, lower Epi dosing
130
What is the preferred treatment for ventricular arrhythmias in the setting of LAST?
Amiodarone
