Regional Anesthesia and Nerve Blocks Flashcards

What dermatomal level of spinal anesthesia is typically required for a cesarean section?

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.

Which of the following is an absolute contraindication to neuraxial anesthesia?

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.

Which local anesthetic is MOST associated with refractory cardiac toxicity and is therefore used at lower concentrations for epidural anesthesia?

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.

The standard epidural test dose detects which two complications?

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.

Which order correctly describes the sequence of nerve fiber blockade by local anesthetics from first to last?

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.

A patient receiving spinal anesthesia develops sudden hypotension and bradycardia. What is the MOST likely mechanism?

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.

What is the primary mechanism of action of local anesthetics?

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.