CRNA Regional Anesthesia and Nerve Blocks 1 — Questions and Answers
Question 1: What dermatomal level of spinal anesthesia is typically required for a cesarean section?
- T4 (Correct answer)
- T6
- T8
- T10
Correct answer: T4
A sensory block to T4 (nipple level) is required for cesarean section to ensure adequate coverage of the uterus, peritoneum, and any diaphragmatic irritation.
Question 2: Which of the following is an absolute contraindication to neuraxial anesthesia?
- Patient anxiety about needles
- Infection at the intended injection site (Correct answer)
- Prior lumbar spine surgery
- Mild thrombocytopenia (platelets 80,000)
Correct answer: Infection at the intended injection site
Infection at the injection site is an absolute contraindication because introducing a needle through infected tissue risks seeding bacteria into the subarachnoid or epidural space, potentially causing meningitis or epidural abscess.
Question 3: Which local anesthetic is MOST associated with refractory cardiac toxicity and is therefore used at lower concentrations for epidural anesthesia?
- Lidocaine
- Chloroprocaine
- Bupivacaine (Correct answer)
- Mepivacaine
Correct answer: Bupivacaine
Bupivacaine has high affinity for cardiac sodium channels and dissociates very slowly ('fast-in, slow-out'), making accidental intravascular injection prone to causing refractory cardiac arrest.
Question 4: The standard epidural test dose detects which two complications?
- Allergic reaction and subarachnoid injection
- Intravascular injection and subarachnoid injection (Correct answer)
- Epidural hematoma and intravascular injection
- Total spinal and allergic reaction
Correct answer: Intravascular injection and subarachnoid injection
The test dose (typically 3 mL of 1.5% lidocaine with 1:200,000 epinephrine) detects intravascular placement via epinephrine-induced tachycardia and subarachnoid placement via rapid dense motor block.
Question 5: Which order correctly describes the sequence of nerve fiber blockade by local anesthetics from first to last?
- Motor → sensory → sympathetic
- Sympathetic → sensory → motor (Correct answer)
- Sensory → sympathetic → motor
- Motor → sympathetic → sensory
Correct answer: Sympathetic → sensory → motor
Smaller, unmyelinated sympathetic B fibers are blocked first, followed by small sensory C and Aδ fibers, then the larger myelinated motor Aα fibers are blocked last.
Question 6: A patient receiving spinal anesthesia develops sudden hypotension and bradycardia. What is the MOST likely mechanism?
- Anaphylaxis to the local anesthetic
- Sympathetic blockade causing venodilation and reduced preload (Correct answer)
- Direct myocardial depression from the local anesthetic
- Vagal response from patient anxiety
Correct answer: Sympathetic blockade causing venodilation and reduced preload
Spinal anesthesia blocks sympathetic fibers, causing vasodilation and venous pooling that reduces preload; bradycardia occurs when cardioaccelerator fibers (T1-T4) are included in the block.
Question 7: What is the primary mechanism of action of local anesthetics?
- Blockade of potassium channels preventing repolarization
- Blockade of voltage-gated sodium channels preventing depolarization (Correct answer)
- Enhancement of GABA-A receptor chloride conductance
- Inhibition of acetylcholinesterase at the neuromuscular junction
Correct answer: Blockade of voltage-gated sodium channels preventing depolarization
Local anesthetics reversibly block voltage-gated sodium channels from the intracellular side, preventing Na+ influx and action potential propagation along the nerve.
CRNA Regional Anesthesia and Nerve Blocks 1
What dermatomal level of spinal anesthesia is typically required for a cesarean section?