Anesthesiology APPLIED Exam › OSCE: echocardiography and POCUS

Volume status, IVC and fluid responsiveness

T1OSCE: echocardiography and POCUS·931 words · ~5 min read·v0.1✓ Sourced · 3DRAFT

Why examiners ask this

"Is this patient fluid responsive?" is the most practical echo question in anesthesia, and the wrong answer drowns a failing heart or starves an empty one. The station tests whether I can separate a static finding (how full the heart looks) from a dynamic one (whether stroke volume will rise with fluid), and whether I know when the IVC lies. It stresses application of knowledge and judgment.

The 60-second answer

I answer volume questions with three looks and one test. First, the LV in short-axis: a small cavity that obliterates in systole with papillary muscles touching means low preload or low afterload. Second, the RV: if it is dilated or the septum is flattened, the heart cannot use more volume and I stop. Third, the IVC in the subcostal long-axis, measured 1–2 cm from the right atrium: a small IVC that collapses more than 50% with a sniff in a spontaneously breathing patient means a low right atrial pressure.¹ Then the test: a passive leg raise or a 250 mL bolus, judged by a change in stroke volume or cardiac output (LVOT VTI, pulse contour), not by blood pressure alone.² Fluid responsiveness is a prediction; the bolus response is the proof. I give fluid only to a patient who is both responsive and in need.

Decision points and the "why"

Static versus dynamic — a small IVC or a small LV says the patient tolerates fluid; it does not prove stroke volume will rise. Dynamic indices, such as respiratory variation of the IVC in a ventilated patient or pulse-pressure variation above about 12–13% with tidal volume over 8 mL/kg, predict response.³ I state which kind of answer I am giving.
Spontaneous breathing IVC — diameter ≤2.1 cm with more than 50% collapse on a sniff estimates a right atrial pressure of about 3 mmHg; over 2.1 cm with less than 50% collapse, about 15 mmHg; anything between, about 8 mmHg.¹ I use it to separate empty from full, not to predict a response to 250 mL.
Ventilated IVC — positive pressure reverses the pattern: the IVC distends on inspiration, and it is commonly dilated and non-collapsing on the ventilator, so its size should not be used to estimate RA pressure.¹ A distensibility index over about 18% predicts responsiveness, but only with tidal volume 8 mL/kg or more, a closed chest and a regular rhythm. Below that, the test is unreliable and I use a passive leg raise.
Plethoric IVC — a fixed, dilated IVC in a hypotensive patient means a full right heart: RV failure, tamponade, tension pneumothorax or PE. That finding stops the fluid and sends me back to the heart and lungs.
Kissing papillary muscles — end-systolic obliteration happens with hypovolemia and with vasodilation. If the IVC is also small, I give fluid; if the IVC is normal, I give a vasoconstrictor.
Passive leg raise — it shifts about 300 mL of venous blood toward the heart, its effect can fade within a minute, and it works with arrhythmias, spontaneous breathing and low tidal volumes.² It is my default test when the IVC is uninterpretable.

The complication they will inject

The patient is hypotensive after induction for a bowel obstruction. The first clip shows a small, hyperdynamic LV with cavity obliteration and an IVC of 0.8 cm that varies widely. I say hypovolemia, give a bolus, and support the pressure with phenylephrine while it runs. The second clip shows the same LV with a new mosaic color jet in the LV outflow tract and the anterior mitral leaflet moving toward the septum in systole. That is systolic anterior motion with dynamic outflow obstruction, made worse by an empty, fast, hyperdynamic heart. I stop any inotrope, give more volume, raise afterload with phenylephrine, slow the heart with esmolol, and deepen anesthesia rather than lighten it. Epinephrine here would worsen the obstruction and the hypotension.

Pitfalls that cost points

Using IVC collapse criteria from spontaneous breathing in a ventilated patient.
Measuring the aorta, or a tangential cut of the IVC, and calling it small.
Giving fluid to a patient with a plethoric IVC and a dilated RV.
Calling "fluid responsive" a reason to give fluid in a patient who is not hypoperfused.
Forgetting raised intra-abdominal pressure, which compresses the IVC and invalidates it.

Rapid-why

Q: Why does the IVC distend on inspiration during mechanical ventilation? A: Positive intrathoracic pressure raises right atrial pressure and impedes venous return, so blood backs up into the compliant cava.

Q: Why is a small LV not proof of hypovolemia? A: Vasodilation lowers end-systolic volume as well, so the cavity obliterates in sepsis or after induction with a normal preload.

Q: When is the IVC useless? A: High PEEP, raised abdominal pressure, severe tricuspid regurgitation, RV failure, or vigorous spontaneous breathing efforts.

Q: Why prefer a passive leg raise? A: It is a reversible fluid challenge that gives no fluid, so a non-responder pays no price.²

Numbers to know

Item	Value
IVC ≤2.1 cm, >50% collapse	RAP ~3 mmHg (0–5)¹
IVC >2.1 cm, <50% collapse	RAP ~15 mmHg (10–20)¹
Ventilated distensibility index	>18% predicts response
Pulse-pressure variation	>12–13% predicts response (Vt >8 mL/kg)³
Passive leg raise	~300 mL autotransfusion²
Test bolus	250–500 mL crystalloid

Sources

1.Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults: An Update from the ASE and EACVI · ASE/EACVI, 2015 · asecho.orgSection V, The Inferior Vena Cava.
2.Passive leg raising: five rules, not a drop of fluid! · Critical Care (Monnet, Teboul), 2015 · pmc.ncbi.nlm.nih.gov
3.Does pulse pressure variation predict fluid responsiveness in critically ill patients? A systematic review and meta-analysis · Critical Care (Yang, Du), 2014 · pmc.ncbi.nlm.nih.govMedian PPV threshold 12% (IQR 10-13%) in patients ventilated with tidal volume >8 mL/kg.

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