POCUS to the rescue : The art of lung ultrasound

14 Feb

Meet Tomas Barry. He is an academic GP and lecturer at UCD with an interest in pre-hospital emergency care. Tomas works as a GP in inner city Dublin and also frequently responds to 999 emergencies with the Dublin Fire Brigade and National Ambulance Service. He recognises the clear potential for POCUS to improve patient care in the prehospital area. This is a clinical case that Tomas compiled while working in the Mater Hospital ED

the case

A 25 year old female collapsed in the ED corridor before arriving to triage. She described a 1 hour history of acute shortness of breath and severe right-sided chest pain

When we delved a little deeper, she reported vague pleuritic chest discomfort over the preceding 2 weeks. She had no medical history and used no regular medications and smoked daily. Her chest was clear to auscultation and she was saturating nicely using 3L of oxygen via facemask, normotensive (127/85 mmHg) but slight tachycardic (100 beats/min)

A list of potential diagnoses for this patient included pulmonary embolus and a pneumothorax

Heart and lung focussed ultrasound is useful to rule in these conditions and we started with a POCUS ‘triple scan’ at the bedside (heart, lung and IVC) [watch this excellent video for more on the ‘Triple scan’]

Normal AP4CH – no gross right ventricle strain
Lung sliding – notice left to right pleural slide and comet tails arising from the pleural line
Reduced lung sliding notice how the pleural line is not moving left and right

By now, we were more suspicious for a pneumothorax and Tomas went in search of a lung point to confirm this diagnosis. He moved the transducer all over the chest wall much like you do when using a stethoscope and recorded these images at the anterior lateral chest wall at the level of the costal margin


Is this a lung point? Lung sliding with an area of lung that is not moving

A chest film showed a small right apical pneumothorax and our patient was observed for a few hours before discharge with appropriate safety net advice and follow up planned at respiratory clinic

discussion

Lung US is fast, accurate and easy to do on every critically ill patient. The sensitivity & specificity of lung US for pneumothorax is higher than CXR

A lung point is highly specific for pneumothorax. However in this case, what we thought was a lung point was in fact a ‘pseudo lung point’. When the transducer is placed on the chest wall over the area where lung meets liver, the image on the screen may appear like a lung point when this is not actually the case. This could lead to a false diagnosis of a pneumothorax! See this excellent video for a better explanation of what happens at the pleural reflection

Impact of lung US in prehospital setting

Acute dyspnoea is a frequent presentation in pre-hospital care and often presents a diagnostic dilemma. Background information can be sparse, environmental noise limits the utility of the stethoscope and the x-ray machine is not to hand. POCUS would refine the differential and working diagnosis in the community or at the roadside. This would help ensure early treatment is targeted at the cause of a patient’s symptoms and transport is to the most appropriate hospital facility

It is imperative that the clinical operator is aware of the limitations of ultrasound and common pitfalls that may occur when scanning. The machine will reproduce a digital image of a physical phenomenon and this must be interpreted in the clinical context of the patient – the machine does not yield the answer, the user does. This is an important concept for a physician sonographer to understand – “your machine has no brain”

Take home message – don’t be fooled by a confirmation bias. Know the limitations of your own skills and of your ultrasound machine. Know common artefacts and what they look like. Be especially careful when you find yourself interpreting discordant clinical and sonographic results

Happy Scannin’!

2 Replies to “POCUS to the rescue : The art of lung ultrasound

  1. This clip impresses more a false lung point than a real one … you can see the diaphragm and the liver to the right of the image

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