Anesthesiology APPLIED Exam › OSCE: echocardiography and POCUS

Abdominal free fluid and gastric ultrasound

OSCE: echocardiography and POCUS·~5 min read· Physician-reviewed✓ Sourced · 5

Stem

Ultrasound station, POCUS task. A 52-year-old man, 80 kg, fell from a ladder and is booked for urgent open reduction of a distal radius fracture; he also bruised his left lower ribs. He drank coffee with cream "a couple of hours ago" and is not sure about food. Supine, the antrum is round and distended with anechoic fluid. In right lateral decubitus it measures 13 cm² and contains no particulate material.

Question

Interpret the gastric scan: does he have a full stomach, and how does it change your anesthetic?

Ideal answer

I interpret a gastric scan in three steps: content, then grade, then volume. The content is clear fluid: anechoic, no particulate or frosted-glass pattern, so this is not solid food.¹ Next the grade: fluid is visible in both supine and right lateral decubitus, which is a grade 2 antrum, and that alone suggests a volume above the safe range.² Then the volume, using the validated formula: 27 plus 14.6 times the right lateral area, minus 1.28 times age.¹ For him that is 27 plus 190, minus 67, about 150 mL, or close to 1.9 mL/kg, above the 1.5 mL/kg cut-off; an area over 10 cm² in an average adult already says the same.² So I treat him as a full stomach. My first choice is to avoid the airway: an infraclavicular or supraclavicular brachial plexus block with light sedation is ideal for a distal radius. If he needs general anesthesia, I do a rapid sequence induction with a cuffed tracheal tube, not a supraglottic airway.² I state the limits too: prior gastric surgery, a gastric band or a large hiatus hernia make the scan unreliable.²

Breaking down the answer

The outline lists the right upper quadrant, left upper quadrant and pelvis for free fluid, and the stomach for content and volume; bladder volume is tested from 2027.³

Window	Probe and position	What I identify
Gastric antrum	Curvilinear 2–5 MHz, epigastric sagittal, supine then RLD¹	Left lobe of liver, antrum, pancreas, aorta or IVC, SMA
Right upper quadrant	Curvilinear, mid-axillary line, marker to head	Liver tip, hepatorenal space, lower pole of kidney, costodiaphragmatic recess⁴
Left upper quadrant	Curvilinear, posterior axillary line, higher and more posterior	Spleen, splenorenal space, lower pole of kidney, recess⁴
Pelvis	Curvilinear, suprapubic, transverse and sagittal	Bladder, rectovesical or rectouterine pouch

Never call it empty supine — the antrum must be scanned in right lateral decubitus before I call the stomach empty, because small volumes move to the dependent antrum.¹
Content beats volume — any thick fluid or solid means a full stomach whatever the volume; volume calculation is only for clear fluid.²
Grade 2 is rare when fasted — over 95% of fasted people show grade 0 or 1, so a grade 2 antrum signals a significant volume.¹
FAST answers one question — in an unstable patient, free fluid sends him to the operating room; I do not try to quantify it, and ultrasound misses solid-organ injury without free fluid.⁵

Follow-up question

The block works and surgery is finished. In recovery his blood pressure falls to 84/50, heart rate rises to 122, and he complains of left upper abdominal pain. On the left upper quadrant view you see an anechoic stripe between the spleen and the kidney, and another above the spleen. What do you do?

Follow-up answer

This is free intraperitoneal fluid in a hypotensive trauma patient, which I treat as blood from a missed splenic injury. I say it aloud to the nurse and call the trauma surgeon now, because a positive FAST in an unstable patient means the operating room, not a CT.⁵ While they come, I place two large-bore IVs, send a type and crossmatch, hemoglobin and coagulation studies, and start blood with a massive transfusion protocol ready. I complete the scan quickly, the right upper quadrant, pelvis and pericardium, without spending time estimating the volume.⁵ I plan a rapid sequence induction, because his stomach is still full. I reassess pressure, heart rate and lactate after each unit.

Pitfalls that cost points

Calling the stomach empty from a supine scan alone.
Applying the volume formula to solid content.
Using a supraglottic airway in a patient with a grade 2 antrum.
Sending an unstable patient with a positive FAST to CT.
Treating a negative FAST as proof of no solid-organ injury.

Rapid-fire

Q: What does a frosted-glass antrum mean? A: A recent solid meal; air mixed with solid blurs the posterior wall.¹

Q: Which LUQ landmarks make an adequate view? A: The inferior and superior poles of the spleen, the inferior pole of the kidney and the left costodiaphragmatic recess.⁴

Q: How much pelvic fluid is physiologic in a woman of reproductive age? A: Up to about 50 mL in the rectouterine pouch; more suggests pathology in trauma.⁴

Q: How sensitive is FAST for hemoperitoneum? A: About 85–96%, with specificity over 98%; small volumes are missed.⁵

Numbers to know

Item	Value
Gastric volume formula	27 + 14.6 × RLD CSA − 1.28 × age (mL)¹
Full stomach, clear fluid	≥1.5 mL/kg or CSA >10 cm² (RLD)²
Gastric probe	Curvilinear 2–5 MHz¹
Antrum depth	Usually 3–4 cm¹
FAST sensitivity / specificity	85–96% / >98%⁵
Ultrasound detection	~85% sensitive only above 150–200 mL⁵

Sources

1.Gastric ultrasound: image acquisition · gastricultrasound.org (Perlas, Van de Putte) · gastricultrasound.org
2.Gastric ultrasound: image interpretation and cut-off values · gastricultrasound.org (Perlas, Van de Putte) · gastricultrasound.org
3.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.orgAbdomen: RUQ, LUQ, pelvis (free fluid; bladder volume from 2027), gastric content and volume.
4.Extended Focused Assessment with Sonography for Trauma in the Emergency Department: A Comprehensive Review · J Clin Med, 2025 · ebi.ac.ukOpen-access full text (PMC12112529) via Europe PMC; window landmarks and pelvic fluid.
5.Focused Assessment with Sonography for Trauma (FAST) · J Med Ultrasound (Savoia et al.), 2023 · ebi.ac.ukOpen-access full text (PMC10413405) via Europe PMC.

Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.