Vascular POCUS

8.1 DVT — proximal

  • Compressibility: non-compressibility is the key POCUS-positive finding.

  • Diameter asymmetry: greater than 2 mm or greater than 50% relative difference raises suspicion.

  • Colour flow: absent or non-propagating flow supports thrombosis.

  • Echogenicity: compressible echogenic material versus anechoic lumen.

POCUS DVT screening is best for proximal DVT. It does not exclude distal DVT. Negative POCUS with high pretest probability requires formal compression duplex or CTV.

8.2 Carotid Doppler — advanced, trained operator

  • ICA PSV greater than 125 cm/s: moderate stenosis possible.

  • ICA PSV greater than 230 cm/s: high-grade stenosis possible.

  • ICA/CCA ratio greater than 4: supports significant ICA stenosis.

POCUS may detect abnormal waveforms or velocities. Do not definitively diagnose carotid stenosis without a trained operator and local protocol.

8.3 Renal Doppler

  • RI 0.5–0.7: often normal.

  • RI greater than 0.8: increased resistance; intrinsic renal disease, obstruction, renovascular disease.

  • RI less than 0.4: low resistance; AV fistula or shunting.

This is a screening parameter, not definitive diagnosis.

8.4 Aorta-focused POCUS

Aorta-focused POCUS is a focused bedside approach to screen for aneurysmal disease, detect acute aortic pathology, and rapidly identify intraluminal thrombus or occlusion. It is a triage, screening, and rule-in tool, not a replacement for CTA, MRA, or formal echocardiography when definitive anatomic characterization or surgical planning is required.

Four Ss approach

  • Superior intercostal/superior parasternal view: proximal to mid ascending aorta.

  • Small-scale parasternal view: descending thoracic aorta posterior to the left atrium.

  • Subxiphoid view: distal descending aorta to abdominal aorta.

  • Suprasternal notch view: aortic arch to proximal descending aorta.

Additional views:

  • Parasternal long-axis: aortic root, proximal ascending aorta, aortic valve, pericardial effusion, indirect type A dissection signs.

  • Abdominal midline longitudinal: infrarenal abdominal aorta to bifurcation.

  • Abdominal transverse: abdominal aorta at renal artery and bifurcation levels.

Aortic diameter thresholds

  • Significant thoracic aortic dilatation: approximately 4 cm or greater.

  • Abdominal aortic aneurysm: commonly 3 cm or greater in maximum short-axis diameter.

  • Aneurysm may also be conceptualized as approximately 1.5 times the normal aortic diameter.

  • AAA follow-up or specialist referral is warranted for newly diagnosed significant dilatation, interval growth, particularly greater than approximately 1 mm/year, saccular morphology, high-risk features, or symptoms suggesting acute expansion or rupture.

Performance for AAA

  • Sensitivity for AAA detection: 94–100%.

  • Negative predictive value: 98.6–100%.

  • EM resident ultrasound accuracy versus CT for AAA: within approximately 4.4 mm.

Aortic dissection and acute aortic syndrome

Direct sonographic signs:

  • A flap separating two aortic lumens: overt dissection.

  • Circular or crescent-shaped aortic wall thickening greater than 5 mm: intramural haematoma.

  • Crater-like outpouching with jagged edges: penetrating atherosclerotic ulcer, dissection, or impending rupture.

Indirect type A signs:

  • Thoracic aortic dilatation.

  • Pericardial effusion or tamponade.

  • Aortic valve regurgitation on colour Doppler.

Reported performance:

  • In one ED POCUS aortic dissection protocol, Stanford type A sensitivity was 100% and type B sensitivity was 93.7%.

  • In a POCUS-first approach, mean time to diagnosis of Stanford type A dissection was reduced by approximately 146 minutes.

Practical interpretation:

  • POCUS is valuable for rapid identification of high-risk findings, triage of unstable patients, early detection of pericardial effusion, aortic regurgitation, or visible intimal flap, and reducing time to diagnosis when a structured protocol is used.

  • A negative POCUS does not exclude dissection, particularly if imaging is limited by body habitus, air, bowel gas, or operator experience.

  • Definitive evaluation generally requires CTA or MRA when clinical suspicion remains high.

Acute abdominal aortic occlusion

Typical presentation:

  • Sudden lower-extremity weakness.

  • Bilateral lower-limb numbness or paraesthesia.

  • Absent or diminished femoral pulses.

  • Cold extremities.

  • Severe abdominal or pelvic pain.

  • Metabolic acidosis with elevated lactate.

  • Neurologic features mimicking stroke or spinal cord pathology.

Key data:

  • Most cases are infrarenal.

  • Mean delay from presentation to diagnosis in one case series was approximately 24 hours.

  • Combined morbidity/mortality range: 21–74%.

Sonographic technique:

  • Longitudinal midline view from xiphoid to bifurcation.

  • Extend distal to bifurcation when possible.

  • Use colour and pulsed-wave Doppler.

  • Identify absent, diminished, or turbulent flow.

  • Differentiate aorta from IVC.

  • Search for intraluminal thrombus, often along the anterolateral wall.

  • The aorta may be normal in calibre despite complete occlusion.

  • Evaluate distal vessels when possible, recognizing bowel gas may limit pelvic visualization.

Action:

  • If occlusion is identified or strongly suspected, expedite vascular surgery consultation and CTA if the patient condition allows.

8.5 Pitfalls

  • Air and bowel gas may obscure the arch, distal descending thoracic aorta, iliac arteries, and distal abdominal aorta.

  • Body habitus and obesity reduce resolution.

  • A negative POCUS does not exclude dissection.

  • Normal aortic calibre does not exclude occlusion.

  • Branch vessels may not be fully assessable at bedside.

  • Definitive imaging is generally required for surgical planning.

DVT/arterial-specific pitfalls

  • POCUS DVT is best for proximal DVT. It does not exclude distal DVT.

  • Negative POCUS in high clinical probability requires formal compression duplex or CTV.

  • Vein diameter is nonspecific; asymmetry is more useful than absolute diameter.

  • Carotid and renal Doppler require significant training; if not trained, limit to basic waveform and refer.

  • Do not definitively diagnose carotid stenosis without trained operator and local protocol.

  • POCUS DVT is screening, not definitive exclusion.

Aortic-specific pitfalls

  • Assuming a negative POCUS excludes aortic dissection.

  • Assuming normal abdominal aortic diameter excludes acute aortic occlusion.

  • Stopping the abdominal aortic scan before the bifurcation when occlusion is suspected.

  • Failing to use Doppler to differentiate aorta from IVC and to detect absent distal flow.

  • Treating POCUS as definitive when CTA/MRA is required for surgical planning.

  • Missing indirect type A signs: pericardial effusion, aortic regurgitation, thoracic aortic dilatation.

  • Ignoring bowel gas, body habitus, and limited branch-vessel visualization.