Neuraxial pharmacology-ChatGPT Flashcards
(128 cards)
1
Q
What is the most common type of local anesthetic allergy?
A
Ester allergies, due to the production of para-aminobenzoic acid (PABA).
2
Q
Is there cross-sensitivity between ester and amide local anesthetics?
A
No, there is no cross-sensitivity between esters and amides.
3
Q
What preservative in amide local anesthetics may mimic PABA and cause reactions?
A
Methylparaben.
4
Q
What factor primarily influences the onset of action of a local anesthetic?
A
Primarily pKa — agents with a pKa closer to physiologic pH have a faster onset.
5
Q
What property of a local anesthetic determines its potency?
A
Lipid solubility — higher lipid solubility increases potency.
6
Q
What determines the duration of action of a local anesthetic?
A
Protein binding — greater protein binding means longer duration.
7
Q
What plasma protein mainly binds local anesthetics?
A
Alpha-1 acid glycoprotein.
8
Q
In what order are peripheral nerves blocked by local anesthetics?
A
1st: B fibers
2nd: C fibers
3rd: Small diameter A fibers
4th: Large diameter A fibers
9
Q
What type of chemical compounds are local anesthetics?
A
Weak bases.
10
Q
Why do local anesthetics with a pKa close to physiologic pH have a faster onset?
A
More molecules are in the non-ionized (lipid-soluble) form, allowing faster membrane penetration.
11
Q
Five
What factors influence vascular uptake and plasma concentration of local anesthetics?
A
Site of injection
Tissue blood flow
Physicochemical properties
Metabolism
Addition of a vasoconstrictor
12
Q
What is baricity in spinal anesthesia?
A
The density of a local anesthetic (LA) solution compared to cerebrospinal fluid (CSF).
13
Q
What is the behavior of an isobaric solution in CSF?
A
Density = CSF; the solution tends to remain near the injection site.
14
Q
What is the behavior of a hyperbaric solution in CSF?
A
Density > CSF; the solution sinks and moves downward from the injection site.
15
Q
What is the behavior of a hypobaric solution in CSF?
A
Density < CSF; the solution rises upward from the injection site.
16
Q
Where are the high points (apexes) in the spinal column for baricity flow?
A
C3 and L3.
17
Q
Where are the low points (troughs) in supine position in the spinal column for baricity flow?
A
T6 and S2.
18
Q
How does local anesthetic spread in the CSF after spinal injection?
A
Simultaneously cephalad and caudad from the injection site.
19
Q
What characteristic of local anesthetics facilitates their uptake into the spinal cord?
A
Lipid solubility.
20
Q
Do local anesthetics undergo metabolism within the CSF?
A
No, there is no metabolism in CSF.
21
Q
How are local anesthetics eliminated from the spinal cord/CSF?
A
Through vascular reabsorption (e.g., vessels in the pia mater).
22
Q
Why do lipophilic drugs (e.g., bupivacaine) have slower reuptake?
A
They have a high affinity for epidural fat, leading to prolonged duration.
23
Q
Which has a longer duration: bupivacaine or lidocaine?
A
Bupivacaine — due to its lipophilicity and slower reuptake.
24
Q
How does local anesthetic spread in the epidural space?
A
It spreads both cephalad and caudad from the catheter insertion site.
25
# To avoid three situations:
Why is incremental dosing important in epidural anesthesia?
To avoid:
- Accidental high spinal
- Rapid hypotension from sudden sympathectomy
- Local anesthetic systemic toxicity (LAST)
26
What is the purpose of adding epinephrine to an epidural test dose?
It serves as an IV marker, helping identify intravascular injection by detecting HR changes.
27
What is the typical onset time for epidural local anesthetics?
10–25 minutes
28
What concentrations does 2-chloroprocaine come in?
2% and 3% solutions.
29
What are key features of 3% 2-chloroprocaine?
- Common in obstetrics
- Rapid onset
- Short duration (due to metabolism by plasma cholinesterase)
- Requires redosing every 45 minutes
- It is an ester anesthetic
30
What is the purpose of alkalinizing a local anesthetic solution?
Increases the nonionized fraction → improves lipid solubility → faster onset.
31
How is alkalinization of an epidural LA achieved?
By adding 1 mEq of sodium bicarbonate (NaHCO₃) per 10 mL of LA.
32
What does increasing the pH of a local anesthetic solution do?
Increases the concentration of nonionized free base, which enhances diffusion across nerve membranes.
33
What is the typical initial dose of local anesthetic for epidural anesthesia?
1–2 mL per spinal segment to be anesthetized.
34
What is the recommended top-up dose for an epidural block?
50–75% of the initial dose, given before the block regresses more than 2 dermatomes.
35
When should the top-up dose be administered?
Before the block regresses more than 2 dermatomes to maintain adequate anesthesia.
36
How does epidural space anatomy affect anesthetic spread?
The epidural space is narrower in the thoracic region, leading to greater cephalad spread than in the lumbar area.
37
How does the volume of local anesthetic affect the epidural block?
Volume primarily determines the height (dermatomal spread) of the block.
38
How does the concentration of local anesthetic affect the epidural block?
It determines the density or intensity of the block (e.g., sensory vs. motor).
39
What is a 'walking epidural,' and how is it achieved?
A low-concentration epidural block (e.g., dilute bupivacaine) that provides analgesia while preserving motor function—often used in labor in europe.
40
What strategy allows anesthetic level to be extended without losing block effectiveness?
Administering a top-up dose before significant regression occurs.
41
Why must dosing adjustments be made based on patient size and anatomy?
Spread and absorption vary with height, epidural space compliance, and spinal anatomy.
42
What are the three primary goals of neuraxial pharmacologic adjuncts?
Postoperative analgesia, Prolonged duration of the block, Improved density of anesthesia
43
Which adjuncts improve analgesia and density, but not duration?
Opioids (e.g., fentanyl, sufentanil, morphine)
44
Which adjuncts improve analgesia, density, and duration?
Alpha-2 agonists (e.g., dexmedetomidine, clonidine)
45
Which adjuncts extend duration only, with no effect on density or analgesia?
Vasopressors (e.g., epinephrine, phenylephrine)
46
What are some investigational or off-label adjuncts used neuraxially?
Neostigmine, magnesium, ketamine, and midazolam (Versed)
47
Where do neuraxial opioids exert their analgesic effect?
Substantia gelatinosa (Lamina II) of the dorsal horn of the spinal cord.
48
What is the mechanism of action of neuraxial opioids?
↓ cAMP production, ↓ Ca²⁺ influx, ↑ K⁺ efflux ➡️ Hyperpolarizes neurons and reduces neurotransmitter release.
49
Do neuraxial opioids enter systemic circulation?
Yes, they can diffuse into the bloodstream and affect systemic opioid receptors.
50
What is the benefit of combining opioids with local anesthetics in neuraxial anesthesia?
Produces a stronger, denser block with synergistic analgesia.
51
What is the onset time of neuraxial morphine?
30–60 minutes
52
What is the duration of action of neuraxial morphine?
6–24 hours
53
What is the CSF spread of morphine?
Wide rostral spread (travels far up the spinal cord)
54
Why does morphine have a delayed risk of respiratory depression?
Due to slow rostral spread and prolonged CSF residency.
55
What is the onset time of neuraxial fentanyl or sufentanil?
5–10 minutes
56
What is the duration of action of neuraxial fentanyl/sufentanil?
2–4 hours
57
What is the CSF spread of lipophilic opioids?
Limited; minimal rostral spread.
58
When does respiratory depression occur with lipophilic opioids?
Typically early after administration.
59
What is the advantage of intrathecal opioid administration?
Immediate and potent analgesic effect due to direct diffusion into the spinal cord.
60
Why do epidural opioids require higher doses than intrathecal?
They must diffuse through epidural fat and dura to reach the spinal cord; only a portion reaches target.
61
How do epidural opioids differ in onset and duration vs intrathecal opioids?
Slower onset, Longer diffusion time, Less targeted analgesia
62
What is the most common side effect of neuraxial opioids?
Pruritus (itching), especially with morphine.
63
What is the incidence of pruritus with intrathecal morphine?
30–100%
64
What are treatment options for opioid-induced pruritus?
Benadryl (25–50 mg IV), Naloxone (0.1 mg IV) – most effective, Buprenex (partial agonist-antagonist)
65
What are prophylactic options to reduce pruritus?
- Limit morphine dose to < 300 mcg
- Ondansetron 4 mg IV
- Nalbuphine (Nubain) 2.5–5 mg IV
66
What type of opioid most commonly causes delayed respiratory depression?
Hydrophilic opioids (e.g., morphine)
67
What dose of intrathecal morphine is associated with minimal risk of respiratory depression?
< 100 mcg
68
What must be done if intrathecal morphine is used?
Continuous apnea monitoring with:
- Capnography
- Pulse oximetry
- Alarm systems
69
What is the legal implication of failing to monitor respiratory depression in outpatient spinal cases?
High risk of malpractice litigation and adverse events.
70
What is the dose-dependent side effect of neuraxial opioids related to GI symptoms?
Nausea — often seen with morphine >300 mcg.
71
What is the incidence of urinary retention with neuraxial opioids?
30–40%
72
What combination of opioids increases the incidence of respiratory depression, nausea, and urinary retention?
Fentanyl/Sufentanil + Morphine
73
What are treatment options for opioid-induced nausea?
Ondansetron (5-HT3 antagonist)
Naloxone (0.1 mg IV)
Phenergan (12.5–25 mg IM)
74
What are the clinical benefits of using α₂ agonists as neuraxial adjuncts?
Prolongs sensory and motor block
Improves analgesia and density of the block
75
By how much do clonidine and dexmedetomidine prolong a neuraxial block?
Approximately 1 hour
76
What are common side effects of α₂ agonists in neuraxial anesthesia?
Hypotension
Bradycardia
Sedation
77
What is the typical intrathecal dose of dexmedetomidine as an adjunct?
3 mcg
78
What is the usual dose of clonidine for neuraxial use?
15–45 mcg
79
What is the main role of vasoconstrictors in neuraxial anesthesia?
Prolong the duration of local anesthetic block by reducing vascular uptake.
80
Do vasoconstrictors enhance block density or analgesia?
No — they extend duration only.
81
What is the typical neuraxial dose of epinephrine when used as an adjunct?
0.2–0.3 mg, sometimes called an “epi wash”
82
What is the usual dose of phenylephrine for neuraxial use?
2–5 mg
83
When added to tetracaine, vasoconstrictors have what effect?
Profound increase in block duration.
84
How do vasoconstrictors affect bupivacaine or lidocaine duration?
They provide a variable (less consistent) increase in duration.
85
Why should anticoagulants be paused before neuraxial anesthesia?
To reduce the risk of epidural hematoma, which can lead to spinal cord compression and permanent neurological damage.
86
What are hallmark symptoms of an epidural hematoma?
Lower extremity weakness and numbness
Low back pain
Bowel/bladder dysfunction
87
What is the treatment window for epidural hematoma to optimize recovery?
Surgical decompression within 8 hours.
88
Why are patients with cardiac stents a unique concern for neuraxial anesthesia?
Stopping antiplatelets → ↑ risk of stent thrombosis
Continuing them → ↑ risk of neuraxial bleeding
89
What is the mechanism of action of COX inhibitors like aspirin and NSAIDs?
Inhibit cyclooxygenase, preventing formation of thromboxane A2, which is needed for platelet aggregation.
90
What is the significance of aspirin use for secondary prophylaxis in surgical patients?
Stopping aspirin in these patients may trigger acute coronary events
91
How do ASA guidelines categorize aspirin holding based on procedure risk?
High-/Intermediate-risk surgery: Hold aspirin 4–6 days
Low-risk surgery or neuraxial block: No need to hold.
92
Does ASA distinguish between 81 mg and 325 mg aspirin for neuraxial blocks?
No, both are treated the same in guidelines — no extra precautions needed for neuraxial placement.
93
Are COX inhibitors (NSAIDs, aspirin) a contraindication to central neuraxial blocks?
No — neuraxial procedures can generally proceed without additional precautions.
94
What is the mechanism of action of GP IIb/IIIa inhibitors?
Inhibit platelet aggregation by blocking fibrinogen binding to platelet surface receptors.
95
What are examples of GP IIb/IIIa inhibitors?
Tirofiban (Aggrastat), Eptifibatide (Integrilin), Abciximab (ReoPro)
96
What are ASRA timing recommendations for GP IIb/IIIa inhibitors?
- Tirofiban/Eptifibatide: Hold for 4–8 hours
- Abciximab: Hold for 24–48 hours.
97
What is the mechanism of action of thienopyridines (e.g., clopidogrel)?
Inhibit platelet aggregation by blocking ADP receptors on platelets.
98
What are examples of thienopyridines?
Clopidogrel (Plavix), Prasugrel (Effient), Ticlopidine (Ticlid)
99
How long should thienopyridines be held before neuraxial procedures?
Clopidogrel: 5–7 days, Prasugrel: 7–10 days, Ticlopidine: 10 days.
100
What is the mechanism of action of unfractionated heparin?
Potentiates antithrombin III, inhibiting thrombin (Factor IIa) and Factors IX, X, XI, and XII.
101
What are ASRA guidelines for holding unfractionated heparin before neuraxial anesthesia?
- Low dose ( <5,000U SC ):
Hold 4–6 hours
- Moderate dose ( ≤20,000 U/day): Hold 12 hours
- Therapeutic dose ( >20,000 U/day or pregnancy): Hold 24 hours.
102
What must be checked if UFH is used for more than 4 days before neuraxial block?
Platelet count, to rule out heparin-induced thrombocytopenia (HIT).
103
What is the mechanism of action of LMWH?
Inhibits Factor Xa.
104
What are examples of LMWH agents?
Enoxaparin (Lovenox), Dalteparin (Fragmin), Tinzaparin (Innohep).
105
What is the timing recommendation before neuraxial block with prophylactic LMWH?
Wait at least 12 hours after the last dose.
106
What is the timing recommendation before neuraxial block with therapeutic LMWH dosing?
Wait at least 24 hours.
107
What lab should be checked if the patient is on LMWH >4 days?
Platelet count.
108
What may be considered in elderly or renally impaired patients on LMWH?
Measuring anti-Xa activity.
109
What is the mechanism of action of warfarin?
Inhibits synthesis of vitamin K-dependent clotting factors: II, VII, IX, and X.
110
What is the recommended hold time for warfarin before neuraxial block?
5 days
111
What lab value must be verified before placing a neuraxial block in a patient previously on warfarin?
INR must be < 1.5
112
What is the mechanism of fibrinolytics?
Convert plasminogen to plasmin, which breaks down fibrin and dissolves clots.
113
Are fibrinolytics safe to use with neuraxial anesthesia?
No — they are contraindicated due to the risk of catastrophic bleeding.
114
What is the mechanism of most DOACs?
Inhibition of Factor Xa or direct thrombin inhibition.
115
What are examples of Factor Xa inhibitors among DOACs?
Apixaban (Eliquis), Betrixaban (Bevyxxa), Edoxaban (Lixiana), Rivaroxaban (Xarelto)
116
What DOAC is a direct thrombin inhibitor?
Dabigatran (Pradaxa)
117
What is the minimum recommended discontinuation time for DOACs before neuraxial anesthesia?
At least 72 hours
118
If a neuraxial block is required <72 hours after last DOAC dose, what should be considered?
Check drug-specific levels (e.g., anti-Xa activity, thrombin time, PT/aPTT/PLT). Delay block if possible for safety.
119
Bupivacaine 0.5%-0.75%
Dose (T10):
Dose (T4):
Onset:
Duration:
- Dose (T10): 10-15mg
- Dose (T4): 12-20mg
- Onset: 4-8 min
- Duration: 130-220min
120
Levobupivacaine 0.5%
Dose (T10):
Dose (T4):
Onset:
Duration:
- Dose (T10): 10-15mg
- Dose (T4): 12-20mg
- Onset: 4-8min
- Duration: 140-230min
121
Ropivacaine 0.5-1%
Dose (T10):
Dose (T4):
Onset:
Duration:
- Dose (T10): 12-18mg
- Dose (T4): 18-25mg
- Onset: 3-8min
- Duration: 80-210min
122
2-Chloroprocaine 3%
Dose (T10):
Dose (T4):
Onset:
Duration:
Dose (T10): 30-40mg
Dose (T4): 40-60mg
Onset: 2-4 min
Duration: 40-90min
123
Tetracaine 0.5-1%
Dose (T10):
Dose (T4):
Onset:
Duration:
- Dose (T10): 6-10mg
- Dose (T4): 12-16mg
- Onset: 3-5min
- Duration: 90-120min
124
Fentanyl
SAB Dose:
Epidural Dose:
Epidural Infusion Dose:
SAB Dose: 10-25mcg
Epidural Dose: 50-100mcg
Epidural Infusion Dose: 25-100mcg/hr
125
Sufentanil
SAB Dose:
Epidural Dose:
Epidural Infusion Dose:
SAB Dose: 5-10mcg
Epidural Dose: 25-50mcg
Epidural Infusion Dose: 25-100mcg/hr
126
Hydromorphone
SAB Dose:
Epidural Dose:
Epidural Infusion Dose:
SAB Dose: N/A
Epidural Dose: 0.5-1mg
Epidural Infusion Dose: 0.1-0.2mg/hr
127
Meperidine
SAB Dose:
Epidural Dose:
Epidural Infusion Dose:
SAB Dose: 10mg
Epidural Dose: 25-50mg
Epidural Infusion Dose: 10-60mg/hr
128
Morphine
SAB Dose:
Epidural Dose:
Epidural Infusion Dose:
SAB Dose: 0.25-0.3mg
Epidural Dose: 2-5mg
Epidural Infusion Dose: 0.1-1mg/hr
