Anesthesiology APPLIED Exam › OSCE: application of ultrasound

Interscalene, supraclavicular, infraclavicular, axillary

T1OSCE: application of ultrasound·1016 words · ~6 min read·v0.1✓ Sourced · 5DRAFT

Why examiners ask this

The four brachial plexus approaches in the outline cover the shoulder to the hand,¹ and each has a different landmark, sonoanatomy and complication. The examiner runs the machine while I hold the probe; I show the plexus at a named level, state the orientation, identify two structures, and demonstrate where the needle tip should deposit local anesthetic.² It tests application of knowledge and organization, and whether I can match the block to the surgery.

The 60-second answer

I use a linear probe at 6–15 MHz and start every brachial plexus scan from a vessel or a muscle I cannot miss. For the interscalene, I begin transverse at the cricoid level over the carotid and slide laterally until the C5, C6 and sometimes C7 roots appear as round hypoechoic dots stacked between the anterior and middle scalene muscles.³ For the supraclavicular, I sit in the fossa above the clavicle and find the subclavian artery on the first rib with the trunks and divisions lateral and superficial to it. For the infraclavicular, I go parasagittal just medial to the coracoid and find the axillary artery deep to both pectoral muscles with the cords around it. For the axillary, I go transverse in the axilla and find the artery with three nerves around it. I name each structure and state the needle approach: usually in-plane, lateral to medial, with the target named; at the interscalene level I avoid the dorsal scapular and long thoracic nerves that run through the middle scalene.³

Decision points and the "why"

Approach	Probe position	Identifying features	Covers	Main hazard
Interscalene	Transverse, C6 level, lateral neck	C5, C6 and C7 roots "stoplight" between anterior and middle scalene	Shoulder, lateral clavicle, upper arm	Phrenic nerve block and Horner syndrome (expected), vertebral artery, epidural or spinal spread³
Supraclavicular	Coronal oblique, supraclavicular fossa	"Bunch of grapes" lateral and superficial to the subclavian artery, on the first rib and pleura	Arm below the shoulder	Pneumothorax, phrenic block in about half
Infraclavicular	Parasagittal, medial to the coracoid	Axillary artery deep to pectoralis major and minor; lateral, posterior and medial cords around it	Elbow, forearm, hand	Deep target, axillary artery and vein puncture
Axillary	Transverse at the axillary crease	Median anterolateral, ulnar anteromedial, radial posterior to the artery; musculocutaneous in coracobrachialis	Elbow, forearm and hand	Multiple injections, compressible veins hide intravascular injection⁴

Trace the interscalene from below — if the roots are hard to see, I find the plexus beside the subclavian artery and follow it up. That is faster than hunting at C6 and confirms I am on plexus, not on the phrenic nerve or a vessel.
Interscalene volume — the phrenic nerve runs on the anterior scalene and is routinely blocked; typical ultrasound-guided volumes are 10–20 mL.³ Lower volumes (5–10 mL) reduce but do not eliminate hemidiaphragmatic paresis, which is close to universal at 20 mL. In a patient with poor respiratory reserve I choose a lower-volume or a supraclavicular or suprascapular approach.
Supraclavicular "corner pocket" — I inject first at the junction of the artery and the first rib, because the lower trunk lies there and missing it spares the ulnar nerve. Keeping the needle tip in view over the rib, not the pleura, prevents pneumothorax.
Infraclavicular target — a single injection posterior to the artery at about 6 o'clock spreads to all three cords, which are named for their position around the artery, not their position on screen.
Musculocutaneous separately — it leaves the sheath high and runs in the coracobrachialis, so an axillary block without a separate injection there leaves the lateral forearm unblocked.⁴

The complication they will inject

After an interscalene block for shoulder surgery, the patient in recovery has a saturation of 90% and is dyspneic. I recognize ipsilateral phrenic nerve block, the expected effect, and the examiner wants me to confirm it and exclude pneumothorax. I scan the diaphragm below the costal margin: paradoxical cranial motion on a sniff confirms paralysis. I scan the anterior chest: lung sliding excludes pneumothorax. I sit the patient up, give supplemental oxygen, and reassure them that the block wears off with the local anesthetic. If the saturation keeps falling, I support with noninvasive ventilation. The other variant is a patient who becomes agitated, then seizes, during injection: local anesthetic systemic toxicity; I stop injecting, call for help, manage the airway, treat seizures with a benzodiazepine, and give 20% lipid emulsion.⁵

Pitfalls that cost points

Calling the first round hypoechoic structure a nerve without checking it with color.
Using 20 mL for an interscalene in a patient who cannot tolerate a hemidiaphragm.
Advancing the supraclavicular needle without seeing the tip over the rib.
Forgetting the musculocutaneous nerve in an axillary block.
Naming the infraclavicular cords by screen position instead of their relation to the artery.

Rapid-why

Q: Why does the interscalene block spare the ulnar nerve? A: The block targets C5, C6 and sometimes C7, so the inferior trunk (C8–T1), which forms the ulnar nerve, is spared.³

Q: Why are roots hypoechoic and cords hyperechoic? A: Roots are mainly neural tissue; distal nerves have more connective tissue between fascicles, which reflects ultrasound.

Q: Why is the supraclavicular block called the "spinal of the arm"? A: The plexus is compact at the trunks and divisions, so one injection blocks most of the arm quickly.

Q: What vessel must I look for before an interscalene injection? A: The vertebral artery deep to the roots, plus any transverse cervical artery crossing the needle path.

Numbers to know

Item	Value
Interscalene volume (US-guided)	10–20 mL typical;³ 5–10 mL to reduce phrenic block
Hemidiaphragmatic paresis at 20 mL	Near universal
Supraclavicular volume	20–30 mL
Infraclavicular / axillary volume	20–30 mL
Lipid emulsion 20% bolus	~1.5 mL/kg over 2–3 min (>70 kg: ~100 mL), then infusion⁵
Probe	Linear, 6–15 MHz

Sources

1.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.org
2.OSCE Example Scenarios (all stations) · ABA, 2023 · theaba.orgNerve block task template: probe orientation, two structures, needle-tip location for local anesthetic.
3.Interscalene Block · OpenAnesthesia, 2025 · openanesthesia.org
4.Axillary Block · OpenAnesthesia · openanesthesia.org
5.Checklist for Treatment of Local Anesthetic Systemic Toxicity · ASRA, 2020 · asra.com

Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.