Anesthesiology APPLIED Exam › OSCE: application of ultrasound

Transversus abdominis plane

OSCE: application of ultrasound·~5 min read· Physician-reviewed✓ Sourced · 3

Stem

At the ultrasound station, the scenario card describes a 52-year-old woman, 70 kg, after open hysterectomy through a Pfannenstiel incision, with incisional pain in recovery. The standardized patient lies supine. The examiner at the machine asks for the nerve block task: a transversus abdominis plane block. A linear 6–15 MHz probe and a curvilinear probe are available.

Question

Show me the plane: where do you put the probe, which layers do you name, and where does your needle tip go?

Ideal answer

HeadlineThe target is a layer, not a nerve: a lateral TAP for her Pfannenstiel, local anesthetic between internal oblique and transversus abdominis.

Linear 6–15 MHz, curvilinear if obese. Transverse in the mid-axillary line between the costal margin and the iliac crest.
Name the layers from the top. Skin, subcutaneous fat, external oblique, internal oblique, transversus abdominis, then transversalis fascia, peritoneum and moving bowel.
In-plane, anterior to posterior, 1–2 mL saline first. A lens-shaped hypoechoic pocket opening between the two muscles confirms the tip.
Maximum dose before volume, because both sides: about 3 mg/kg of ropivacaine, roughly 210 mg for her 70 kg, the ceiling for both blocks together.
Tell the team its limit. Somatic analgesia of the abdominal wall only, not visceral pain, so it sits inside a multimodal plan.

Breaking down the answer

The plane is the target — TAP is an outline nerve-block target;¹ I show the plane, name two layers, show where the tip deposits local anesthetic,² and say what it covers and what not. Bilateral dose arithmetic is the judgment tested.

Approach	Probe position	Target	Coverage
Lateral TAP	Mid-axillary line, between costal margin and iliac crest	Between internal oblique and transversus abdominis	About T10–T12 (variably to L1), infraumbilical wall
Subcostal TAP	Oblique along the costal margin, medial	Between rectus and transversus abdominis, or along the plane laterally	T6–T9, supraumbilical wall
Posterior TAP	Posterior axillary line, toward the lumbar fascia	Plane near the quadratus lumborum edge	Wider spread, sometimes some visceral benefit

Identify layers by movement — peritoneum and bowel slide with breathing and peristalsis below the transversus abdominis; that deepest moving layer marks where the plane ends and the abdomen begins.
Reading the test volume — before the full dose, a lens confirms the plane; a volume that disappears into muscle means an intramuscular tip; spread below the transversus means preperitoneal or intraperitoneal.
Match the approach to the incision — lateral TAP covers a Pfannenstiel or lower port sites; a midline laparotomy above the umbilicus needs subcostal TAP along the costal margin; a full midline incision needs both bilaterally, or a different block.
Bilateral arithmetic — a four-quadrant TAP uses 60–80 mL, so I fix the maximum dose first and dilute to 0.2–0.25%. Plasma levels peak about 30 minutes after a TAP, later than a brachial plexus block, so I watch recovery for toxicity.
Multimodal partners — acetaminophen, an NSAID if allowed, and a small opioid plan.

Follow-up question

Thirty minutes after a trainee places her bilateral TAP blocks with 80 mL of 0.375% ropivacaine, she complains in recovery of tinnitus and a metallic taste, then has a seizure. What do you do?

Follow-up answer

HeadlineLocal anesthetic systemic toxicity: 300 mg is over 4 mg/kg, timed to the late TAP peak; I call for help and the lipid kit.

I tell the team it is LAST. Airway and oxygen, a benzodiazepine for the seizure, 20% lipid emulsion, small epinephrine doses (under 1 mcg/kg) if needed; I avoid large propofol doses, vasopressin, calcium-channel blockers and beta-blockers.³ I reassess rhythm and pressure continuously and keep monitoring her after she recovers.

Pitfalls that cost points

Advancing unseen with bowel 1 cm deep: a tip below the bright line moving with breathing is peritoneal; withdraw, watch for bleeding or bowel injury.
Bleeding or bowel injury missed in recovery: hypotension, abdominal pain, a falling hemoglobin.

Rapid-fire

Q: Why the plane between internal oblique and transversus abdominis? A: The lower intercostal (T6–T11), subcostal, iliohypogastric and ilioinguinal nerves run in it before supplying the anterior abdominal wall.

Q: Why do TAP plasma levels peak late? A: Fascial planes absorb slowly but steadily across a large surface, so the peak arrives about 30 minutes after injection.

Q: Why add a subcostal injection for a laparotomy? A: The lateral TAP spreads mostly to the lower thoracic segments (about T10–T12, variably L1) and misses the upper abdominal wall.

Q: Why use a curvilinear probe in obesity? A: The muscles can lie more than 5 cm deep, beyond useful linear-probe penetration.

Numbers to know

Item	Value
Volume per side	15–20 mL
Ropivacaine concentration	0.2–0.25%
Ropivacaine maximum	~3 mg/kg
Peak plasma level	~30 min after injection
Lateral TAP coverage	About T10–T12
Subcostal TAP coverage	T6–T9
Lipid emulsion 20% bolus	~1.5 mL/kg over 2–3 min (>70 kg: ~100 mL); maximum 12 mL/kg³

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.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.