Seeing is Believing .. or is it?

In the Eye of the Clinician

Emergency medicine is built on facts - history, physical exam, investigations, action.

And few tools seem as reassuring as real-time imaging. Point-of-care ultrasound (PoCUS) offers exactly that: bedside visuals, fast answers, and a non-invasive view beneath the surface.

But here’s the truth: seeing isn’t always believing.

• Use PoCUS to answer focused, time-sensitive clinical questions - not to go fishing.

• Anchor your interpretation in pre-test probability - not anxiety or optimism.

• Recognize normal findings as valuable - knowing what’s not wrong is crucial.

• Apply structured protocols like SHoC to reduce bias.

• And remember: no image should override the whole clinical picture.

The Trouble with Trusting Your Eyes

Imagine staring at a set of grey lines on a coloured background. Some look darker. Some lighter. But they’re all the same.

The illusion isn’t in the image - it’s in your brain.

Our minds interpret more than they observe - influenced by context, emotion, and expectation. The same is true when we place an ultrasound probe on a patient’s chest, abdomen, or soft tissue.

We see what we’re trained to see - but also what we expect or fear might be there.

PoCUS: The Fastest Second Opinion in Medicine

There’s no denying that PoCUS has transformed emergency care. When used thoughtfully and skillfully, it can rapidly identify:

• Pericardial effusion in tamponade

• Free fluid in blunt trauma

• Pneumothorax missed on CXR

• Heart failure masquerading as pneumonia

• Abscess under cellulitis

It’s portable, safe, repeatable, and increasingly well taught.

But even powerful tools demand restraint.

The Danger of “I See It, Therefore It’s True”

The most common mistake in PoCUS isn’t missing pathology - it’s overinterpreting it.

• Calling any dark stripe “free fluid”

• Declaring cardiac standstill in a slow or unclear view

• Assuming lungs are dry based on one rib space

The solution? Bayesian reasoning.

Ask yourself: How likely is this to be true, based on the whole picture?

Let clinical context - history, vitals, pre-test probability - guide interpretation, not the image alone.

SHoC: A Structured Approach to Shock

To avoid bias, PoCUS should follow structured protocols. One example is the SHoC protocol for undifferentiated shock:

• Cardiac: LV function, pericardial fluid

• IVC: Size and collapsibility

• Lungs: B-lines, pleural effusions, pneumothorax

• Abdomen/Aorta: FAST views, aneurysm

This sequence can help differentiate:

• Hypovolemia

• Cardiogenic shock

• Obstructive causes (tamponade, PE, tension pneumo)

And, more importantly, it helps avoid premature diagnostic closure.

Cardiac Arrest and the PoCUS Paradox

In arrest, PoCUS tempts us to prognosticate: No cardiac motion? Must be futile…

But that’s a dangerous oversimplification.

Studies show that some patients without visible motion on ultrasound have survived. Absence of activity does not equal futility.

The AHA advises caution: use PoCUS only if it doesn’t interrupt compressions. And never let it guide the decision to stop resuscitation.

In cardiac arrest, PoCUS is an adjunct - not a verdict.

For more on cardiac arrest in PoCUS, read here!

Seeing Is (Sometimes) Believing

PoCUS doesn’t give a diagnosis - it gives images. Their meaning depends on training, critical thinking, and a willingness to challenge one’s own assumptions.

Our clinical eyes, like our real ones, can be fooled by shadow, noise, and expectation.

But when used with discipline, humility, and structure, PoCUS remains one of the most transformative tools in emergency medicine.

Final Thoughts

Seeing is believing - sometimes.

Believing, however, should be grounded in context, evidence, and continuous learning.

Keep questioning. Keep learning. And keep scanning.

Follow along:

@PaulAtkinsonEM | @CanPOCUS | @NetworkSHoC