the stratagem of the sheathed probe: when putting down the ultrasound can result in better care (guest post)

By Ben Millette

“Hi Ben, I’ve got a favour to ask: can you come and echo this lady for me please?” 

Corridor consultations such as this arrive not infrequently and I am always flattered to receive them.  This particular request came from one of my anaesthetic colleagues. She had been reviewing a woman in the later stages of pregnancy who had been admitted with shortness of breath.  After assessment, the obstetric team had arranged a CTPA which excluded PE and showed clear lungs but had revealed a worryingly dilated pulmonary artery and a slightly enlarged right ventricle. 

How can I best go about improving the care of this patient? Should I fire up my favourite ultrasound right away or leave it plugged in at the wall and have a bit of a think?

Chapter 3 of Sun Tzu’s Art of War is entitled “The Sheathed Sword”. Within it, he expounds upon the stratagem of the sheathed sword:

“To fight and conquer in all your battles is not supreme excellence; supreme excellence consists in breaking the enemy’s resistance without fighting”

Sun Tzu, The Art of War

Thus, victory is achieved with the sword remaining sheathed.

Does POCUS always optimize patient care? Or are there some circumstances in which it is better for the patient for the probe to remain sheathed too?

I am a great proponent of POCUS guided practice. There are undoubted benefits in rapid diagnostics and procedural guidance that have revolutionized acute care specialities in the last 10 years.  Those who know me will be bemused that I appear to be arguing for using it less.

To clarify, I am simply arguing for the rational application of POCUS to clinical practice.  As in much #zentensivist practice, frequently less is more. Knowing how to best apply them is just as important as possessing POCUS skills in the first place. 

I approach the issue of when to use POCUS by using three simple questions:

What is the clinical question?

Formulate a specific question:

  • Does this patient in cardiac arrest have any signs to suggest a PE?
  • Can I rule out a DVT in this swollen leg?
  • Does this patient have pulmonary edema that requires offloading?

Be as specific as possible to be clear in your thinking.

Can you answer it with the ultrasound equipment and skills that you have available?

Regarding equipment: do you have a handheld ultrasound which may limit your capability or a fully functional cart-based machine?

Assessing one’s own skills can be a tricky area at times. Sun Tzu touches on self-knowledge in chapter 3: “If you know the enemy and know yourself, you need not fear the result of a hundred battles”. Having humility in one’s own skills is a crucial aspect of POCUS. 

Recognizing your limits prevents your overconfidence from harming patients. Many of us have seen POCUS practitioners overinterpreting beyond their skill level and adverse consequences can result from this hubris. I once encountered an intensive care physician with the probe the wrong way around confidently asserting that the RV was dilated. This underlines the importance of self-governance by using cross sectional imaging or departmental echocardiography to cross check your own findings and get feedback on your ability. For trainees, it also means regular assessments with your ultrasound mentor.

What other services are available to help answer this question?

For example, if you suspect a PE in a shocked patient, are they stable enough to confirm or refute the diagnosis with a CTPA? Is there a reduced radiology service at the weekend? Are there others in your hospital with greater skills in echocardiography who could better answer your question? Can a friendly radiologist or cardiologist come to assist you with scanning the patient?

By employing these three questions we can discern whether POCUS is an appropriate investigation for the patient. Sure, you could probably ultrasound the trauma patient’s swollen eye to assess pupil reactivity and get some cool pictures from it, but wouldn’t the patient be better off with an ophthalmologist considering a lateral canthotomy? 

Some may argue, what have you lost by using POCUS on this patient?

Our time is valuable. Knowing how to optimize use of it allows patients to have necessary interventions and investigations all the more quickly. Furthermore, the potential for misdiagnosis in the context of overconfidence must always be borne in mind.

To return to our initial case, I reviewed the patient’s notes and imaging and applied the three questions:

What is the clinical question?

Can I rule out significant cardiac disease in this woman?

Can you answer it with the ultrasound equipment and skills that you have available?

I had access to a fully functional cart-based ultrasound. I have basic accreditation in echocardiography and am developing more advanced skills. I can pick up obvious pathology but would not be able to rule out more subtle forms of cardiac disease. 

Therefore, I did not feel comfortable ruling out significant cardiac pathology in this case.

What other services are available to help answer this question?

It was the weekend, and our echocardiography department has significantly reduced service.  Our local referral centre for maternal medicine has experience in cardiac disease in pregnancy and would not only be able to investigate her appropriately but would be better equipped to manage and arrange her eventual delivery.

I had enough information from the CTPA and clinical history to suggest a high risk of significant cardiac disease and thought it was very unlikely that my echo would change the management of this patient.  I therefore did not perform an echo in this case.  The patient was referred without delay to our tertiary maternal medicine unit.

While POCUS is immensely helpful in many circumstances, sometimes the probe is best left firmly in its sheath.  If Sun Tzu were a zentensivist, I have no doubt he would agree.

Dr. Ben Millette is a consultant in intensive care and anesthesia at Buckinghamshire Healthcare NHS Trust. He has a special interest in POCUS and runs a POCUS fellowship program. His other areas of interest include medical education, antimicrobial stewardship and homemade Mexican food.


  • This post was edited by the site editor and approved by the guest author.
  • Header photo by Wicked Sheila on Unsplash

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s