Anesthesiology APPLIED Exam › OSCE: application of ultrasound

Interscalene, supraclavicular, infraclavicular, axillary

OSCE: application of ultrasound·~5 min read· Physician-reviewed✓ Sourced · 5

Stem

At the ultrasound station, the standardized patient is a 45-year-old man, 85 kg, scheduled for arthroscopic rotator cuff repair, sitting semi-recumbent with his head turned slightly away. The examiner at the machine says today's nerve block task is a brachial plexus block for his shoulder.

Question

Which brachial plexus block do you choose for his shoulder, and how do you find and identify the target with the probe?

Ideal answer

HeadlineInterscalene for a rotator cuff repair, because its roots cover the shoulder and upper arm; I start transverse over the carotid at the cricoid.

Linear 6–15 MHz, carotid first, slide lateral. I cannot miss the carotid; C5, C6 and sometimes C7 roots are round hypoechoic dots stacked between anterior and middle scalene.¹
Roots hard to see: trace up from supraclavicular. Plexus beside the subclavian artery, followed up, also confirms plexus, not phrenic nerve or vessel.
Color Doppler to prove the dots are not vessels and find the vertebral artery deep to the roots.
Freeze, name, needle in-plane lateral to medial. Roots and both scalenes; tip beside the roots, avoiding the dorsal scapular and long thoracic nerves in the middle scalene.¹

Watch for: his breathing afterward: I tell the examiner the phrenic nerve is routinely blocked.

Breaking down the answer

One target, one level — the outline's four approaches cover shoulder to hand;² the examiner runs the machine, I show the plexus, state orientation, identify two structures, and show where the tip deposits local anesthetic.³ Matching block to surgery is the graded judgment.

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 spread¹
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

Interscalene volume — the phrenic nerve runs on the anterior scalene; typical volumes are 10–20 mL.¹ 5–10 mL reduces but does not eliminate hemidiaphragmatic paresis, near universal at 20 mL. Poor reserve: lower volume, or a supraclavicular or suprascapular approach.
Supraclavicular "corner pocket" — first injection at the artery–first rib junction, where the lower trunk lies; missing it spares the ulnar nerve. The tip in view over the rib, not the pleura, prevents pneumothorax.
Infraclavicular target — one 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 on screen.
Musculocutaneous separately — it leaves the sheath high and runs in the coracobrachialis; without a separate injection the lateral forearm stays unblocked.⁴

Follow-up question

After a 20 mL interscalene block and his surgery, he is in recovery with a saturation of 90% on room air and says he cannot take a deep breath. How do you confirm the cause and manage it?

Follow-up answer

HeadlineIpsilateral phrenic nerve block, the expected effect; I tell the recovery nurse I am confirming it and excluding pneumothorax.

I scan the diaphragm below the costal margin: paradoxical cranial motion on a sniff confirms paralysis. On the anterior chest, lung sliding excludes pneumothorax. I sit him up, give supplemental oxygen and reassure him it wears off with the local anesthetic. If the saturation keeps falling, noninvasive ventilation, reassessing until the block regresses.

Pitfalls that cost points

Picking interscalene for a hand case: C8–T1 is spared, leaving the ulnar side unanesthetized.
Working up ipsilateral Horner syndrome after interscalene as a complication; it is an expected effect, explained to the patient beforehand.

Rapid-fire

Q: Why does the interscalene block spare the ulnar nerve? A: It targets C5, C6 and sometimes C7, so the inferior trunk (C8–T1), which forms the ulnar nerve, is spared.¹

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.

Q: The patient becomes agitated, then seizes, during injection. What do you do? A: LAST: stop injecting, call for help, manage the airway, benzodiazepine for the seizure, and 20% lipid emulsion.⁵

Numbers to know

Item	Value
Interscalene volume (US-guided)	10–20 mL typical;¹ 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.Interscalene Block · OpenAnesthesia, 2025 · openanesthesia.org
2.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.org
3.OSCE Example Scenarios (all stations) · ABA, 2023 · theaba.orgNerve block task template: probe orientation, two structures, needle-tip location for local anesthetic.
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.