Diagnostics & Procedures · Topic 5 of 16

Point-of-Care Ultrasound & Echo Basics

Diagnostics · bedside ultrasound

Point-of-Care Ultrasound & Echo Basics

Bedside ultrasound answers fast questions — free fluid, pneumothorax, B-lines, the IVC and the pump — but a negative scan rarely rules anything out.

Key numbers

Bilateral B-lines ≥ 3 per space: edema≥ 3 B-lines per space

Small collapsing IVC: low atrial pressureIVC ≤ 2.1 cm, > 50%

01 · DoFAST: four free-fluid views

FAST looks for free fluid in 4 areas — pericardial (subxiphoid), perihepatic (Morison pouch), perisplenic and pelvic (most sensitive); E-FAST adds the anterior and lateral chest for pneumothorax and pleural fluid.

02 · Look forPneumothorax: no sliding, barcode sign

Pneumothorax on ultrasound: absent lung sliding with A-lines, no B-lines and no lung pulse, and a barcode (stratosphere) sign on M-mode; a lung point is highly specific but is absent in complete pneumothorax.

03 · Defined bySmall collapsing IVC: low atrial pressure

Spontaneously breathing: an IVC ≤ 2.1 cm collapsing > 50% on inspiration suggests right atrial pressure 0–5 mmHg; > 2.1 cm with < 50% collapse suggests 10–20 mmHg (8 mmHg if indeterminate).

Presentation

What you'll see

Tamponade: chamber collapse with plethoric IVCEcho supports tamponade when an effusion comes with right atrial systolic and right ventricular diastolic collapse and a plethoric IVC (< 50% inspiratory collapse); tamponade itself remains a clinical diagnosis.

Dilated RV: right heart failure, think PEThe RV is normally about 60% of LV size and triangular; a dilated RV signals right ventricular failure and may suggest pulmonary embolism, but echo supports risk stratification rather than confirming or excluding PE.

Hyperdynamic, nearly empty LV: hypovolemiaA hyperdynamic LV with almost no blood at end-systole suggests hypovolemia even when the IVC looks full, as can happen in a ventilated patient.

Pleural effusion: anechoic space, spine signPleural fluid appears as a dependent anechoic space between parietal and visceral pleura, often with a spine sign; lung ultrasound (83–100% sensitive) detects effusion better than radiography and guides thoracentesis.

Lung sliding confirms ventilation after intubationBilateral lung sliding (seashore sign on M-mode) helps confirm tube placement when end-tidal CO₂ is unreliable, as in cardiac arrest; absent sliding on one side with a preserved lung pulse suggests mainstem intubation.

Pneumonia: hepatization and dynamic air bronchogramsConsolidated lung looks tissue-like (hepatization) with an irregular shred border and dynamic air bronchograms; B-lines are mostly bilateral in viral and unilateral in bacterial pneumonia.

Diagnosis & monitoring

Work-up

Bilateral B-lines ≥ 3 per space: edema must knowB-lines are vertical artifacts from the pleural line to the screen bottom; ≥ 3 per intercostal space bilaterally with preserved sliding means cardiogenic pulmonary edema. ARDS gives patchy B-lines with spared areas.

Management

Orders

RUSH exam: pump, tank, pipesRUSH for undifferentiated shock checks the pump (contractility, effusion, RV size), the tank (IVC, free fluid) and the pipes (aortic aneurysm, leg DVT); pooled sensitivity 87% and specificity 98% for shock type.

Four cardiac windows: PLAX, PSAX, apical, subxiphoidFocused cardiac ultrasound uses the parasternal long-axis, parasternal short-axis, apical and subxiphoid windows to estimate LV function and wall motion, RV size and pericardial effusion in the hypotensive patient.

The rules

Know these

Positive FAST in unstable patient: intervene must knowE-FAST is moderately sensitive and highly specific: free fluid in an unstable patient calls for immediate intervention (laparotomy, pericardial window, chest tube), but a negative scan does not exclude injury.

IVC size misleads: ventilation, abdomen, RVIVC size and collapse are not a stand-alone volume test: positive-pressure ventilation (use distensibility), intra-abdominal hypertension, RV failure, tricuspid regurgitation and tamponade distort them — integrate heart, lungs and clinical picture.

Pneumothorax or mainstem intubation on lung ultrasound?

Commonly confused

Lung sliding	Absent
Lung pulse	Absent
A-lines	Present
B-lines	None

Commonly confused

Tell apart

Pericardial vs pleural fluid: the descending aortaOn the parasternal long-axis view, pericardial fluid tracks anterior to the descending aorta, whereas a left pleural effusion lies behind it.

More detail

Reference

Show 6 reference facts

The pelvis is the most dependent, earliest-filling view for intraperitoneal fluid; about 5° of Trendelenburg increases sensitivity in the right upper quadrant.

FAST needs on average about 620 mL of intraperitoneal fluid to turn positive (about 400 mL for experts), and free fluid is nonspecific for bowel injury.

A lung pulse (cardiac oscillation at the pleural line) proves the pleural layers are apposed at that spot and rules out pneumothorax there; pleural thickening, adhesions and the heart border can mimic a lung point.

New bilateral B-lines are a nonspecific stop signal during fluid resuscitation — viral pneumonia, ARDS, contusion and interstitial disease produce them too.

Spontaneous breathing: IVC collapsibility = (max − min) ÷ max. Mechanical ventilation: distensibility = (max − min) ÷ min, because the IVC is largest during the ventilator breath.

Loss of lung sliding over 3 anterior intercostal spaces and A-lines are each nearly 100% sensitive for pneumothorax and, together, highly specific.

Pearl

RUSH = pump, tank, pipes: the heart, the IVC and the aorta and leg veins.

Sources · Merck Manual Professional — How To Do E-FAST Examination · Merck Manual Professional — Monitoring and Testing the Critical Care Patient (point-of-care ultrasound) · Nuts and bolts of lung ultrasound: utility, scanning techniques, protocols, and findings in common pathologies. Crit Care 2024 · Merck Manual Professional — Pneumothorax · Inferior vena cava ultrasonography for volume status evaluation: an intriguing promise never fulfilled. J Clin Med 2023 (cites ASE/EACVI right-atrial-pressure criteria) · Inferior vena cava ultrasound and other techniques for assessment of intravascular and extravascular volume: an update. Clin Kidney J 2023 · Monnet X, Teboul JL et al. Using the ventilator to predict fluid responsiveness. Intensive Care Med 2025 · Diagnostic accuracy of Rapid Ultrasound in Shock (RUSH) exam: a systematic review and meta-analysis. Bull Emerg Trauma 2018 · Merck Manual Professional — Pericarditis (pericardial effusion and cardiac tamponade) · Merck Manual Professional — Pulmonary Embolism · WSES guidelines on blunt and penetrating bowel injury: diagnosis, investigations, and treatment. World J Emerg Surg 2022 · Merck Manual Professional — Pleural Effusion · emDocs — 2026 Guideline: Evaluation and Management of Acute PE (summary of the AHA/ACC guideline) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).