BCA Regional Anesthesia Techniques 3 — Questions and Answers
Question 1: Which nerve must be separately blocked to achieve complete anesthesia of the medial forearm when performing an axillary brachial plexus block?
- Medial cutaneous nerve of the forearm (Correct answer)
- Intercostobrachial nerve
- Medial cutaneous nerve of the arm
- Medial pectoral nerve
Correct answer: Medial cutaneous nerve of the forearm
The medial cutaneous nerve of the forearm (MCNF) branches proximal to the axilla and must be blocked separately as it is not reliably anesthetized with standard axillary block.
Question 2: What is the mechanism of action of dexmedetomidine when added to local anesthetic for peripheral nerve blocks?
- Alpha-2 agonist causing hyperpolarization of nerve membranes (Correct answer)
- Sodium channel blockade independent of local anesthetic
- Vasoconstriction reducing local anesthetic absorption
- Direct GABA receptor potentiation
Correct answer: Alpha-2 agonist causing hyperpolarization of nerve membranes
Dexmedetomidine prolongs peripheral nerve block duration via alpha-2 adrenergic receptor-mediated hyperpolarization of peripheral neurons, reducing excitability.
Question 3: A spinal anesthetic with hyperbaric bupivacaine is administered at L3-L4 with the patient in the sitting position. To achieve a sacral block only (saddle block), how long should the patient remain seated?
- 5-10 minutes (Correct answer)
- 1-2 minutes
- 20-30 minutes
- 45-60 minutes
Correct answer: 5-10 minutes
For a saddle block, the patient is kept sitting for 5-10 minutes to allow hyperbaric solution to pool in the dependent sacral and lower lumbar segments before lying down.
Question 4: Which ultrasound view is recommended for visualizing the adductor canal to perform an adductor canal block?
- Short-axis view of the medial thigh at mid-femur level (Correct answer)
- Long-axis view of the femoral artery at the inguinal crease
- Short-axis view at the knee joint line
- Long-axis view of the saphenous nerve at the ankle
Correct answer: Short-axis view of the medial thigh at mid-femur level
The adductor canal block is performed using a short-axis (transverse) ultrasound view at the mid-thigh level, identifying the saphenous nerve adjacent to the femoral artery in the canal.
Question 5: Inadvertent intravascular injection of local anesthetic during a stellate ganglion block would MOST likely cause which immediate symptom?
- Seizure due to vertebral artery injection (Correct answer)
- Bilateral phrenic nerve palsy
- Complete spinal block
- Pneumothorax
Correct answer: Seizure due to vertebral artery injection
The stellate ganglion lies adjacent to the vertebral artery; even 1 mL of intra-arterial local anesthetic injection can cause immediate CNS toxicity and seizure.
Question 6: When performing a continuous femoral nerve catheter, what is the MOST important technique to confirm correct catheter placement?
- Stimulating catheter with motor response (quadriceps twitch) at ≤0.5 mA (Correct answer)
- Loss of resistance to saline technique
- Aspiration of blood to rule out vascular placement
- Nerve stimulation with sensory response only
Correct answer: Stimulating catheter with motor response (quadriceps twitch) at ≤0.5 mA
Stimulating catheters confirm placement by eliciting a quadriceps twitch at ≤0.5 mA, indicating the catheter tip is adjacent to the femoral nerve.
Question 7: In a patient with severe COPD on home oxygen, which regional anesthetic technique is CONTRAINDICATED due to risk of respiratory failure?
- Bilateral interscalene blocks (Correct answer)
- Unilateral femoral nerve block
- Bilateral adductor canal blocks
- Unilateral TAP block
Correct answer: Bilateral interscalene blocks
Bilateral interscalene blocks cause bilateral phrenic nerve palsy (100% incidence per side), which can precipitate respiratory failure in patients with severely limited pulmonary reserve.
BCA Regional Anesthesia Techniques 3
Which nerve must be separately blocked to achieve complete anesthesia of the medial forearm when performing an axillary brachial plexus block?