Your team is being deployed to Africa. One of your teammates has had a respiratory infection for the past week. A few hours after a 14-hour flight, he comes to you reporting shortness of breath and pain on the right side of his chest whenever he takes a deep breath.
You evaluate this otherwise healthy 29-year-old male starting with a set of vital signs:
- Heart rate 90 beats/min
- Blood pressure 120/65mmHg
- Respiratory rate 24/min
- SpO2 95% on room air
- Temperature 38.0°C (100.4°F)
On physical examination, the patient is taking shallow breaths but he is not in respiratory distress. He is warm to touch, and he has notably decreased breath sounds over the lower right lateral side of his chest. The reminder of his examination is unremarkable.
As part of your evaluation, you obtain an ultrasound of his lungs. While viewing a dynamic clip, you are able to make a diagnosis.
- What is the most likely diagnosis, and what suggestive findings are present in Figure 1?
- What dynamic findings pathognomonic for this diagnosis would you expect to see in Video 1?
- What is the Pulmonary Embolism Rule-out Criteria (PERC) rule, and how does it help you in this case?
Long flight… Pleuritic chest pain (pain with respirations)… It surely rings the bell of pulmonary embolism (PE), which of course sounds like a real disaster (a.k.a cluster F) for a SOF operator who barely arrived at their deployed location.
But let’s back off here and think this through. This shortcut medicine doesn’t quite work so well in austere settings with limited diagnostic and therapeutic capabilities. It’s not an emergency room where you can work them up for just about anything remotely emergent.
Here we have a young and otherwise very healthy male SOF operator (thus neither a Gruntma nor a G.I. Jane) who had signs and symptoms of a respiratory infection for 1 week prior to onset of his current symptoms. If it wasn’t for that long flight, you wouldn’t even think of a PE. So what else can you put on your focused list of potential DDx (differential diagnosis)?
- Pneumonia (treatable locally)
- Pleural effusion/parapneumonic effusion (treatable locally)
- Musculoskeletal chest wall pain (Rx: raised eyebrows and a touch of vit. M)
- Pulmonary embolism (needs to be shipped back)
We all seem to be very concerned about PE’s when it comes to long-distance air travel. On one hand, rightly so, because such long-haul flights are a recognized risk factor for venous thromboembolism (VTE) events such as PE and DVT (deep vein thrombosis). However, that risk is generally very small . Even though it increases with the distance traveled (range: <2500 km, 0 cases; ≥10,000 km, 4.77 cases per million travelers) , most people who develop travel-associated blood clots have one or more other risks for blood clots, such as:
- Older age (risk increases after age 40)
- Obesity BMI > 30
- Recent surgery or injury (within 3 months)
- Use of estrogen-containing contraceptives (just for G.I. Janes)
- Hormone replacement therapy (generally for Gruntmas)
- Pregnancy and the postpartum period (up to 3 months after childbirth)
- Previous blood clot or a family history of blood clots
- Active cancer or recent cancer treatment
- Limited mobility (for example, a leg cast)
- Catheter placed in a large vein
- Varicose veins 
And our SOF operator does not meet any of the above criteria. It is also rather unlikely he stayed glued to his seat for the duration of flight. He might have been somewhat hangover and therefore dehydrated, but this in itself is not a reason to consider him a high risk patient. Therefore, even though we should go through a mental exercise of considering PE in his case, we can surely apply the PERC rule (Pulmonary Embolism Rule-out Criteria) and rule him out.
You may also apply another risk stratification tool, namely Geneva Score (Revised) for Pulmonary Embolism (rGeneva), which in my perception is a far better tool for a SOF Medic who may otherwise lack that gut feeling (i.e. experience/clinical gestalt) about the possibility of PE. Clinical gestalt is part of the Well’s Criteria for Pulmonary Embolism (Wells’) as one of the scored items literally asks you to determine if “PE is #1 diagnosis OR equally likely“.
Let’s imagine the air crew has already left, and they could not possibly fly back to your location in the next 4 days. In this situation, it is quite important to try making the right diagnosis and initiating the appropriate treatment. Of course, it is one of those cases you would want to talk through with your telemedicine consultants (for U.S. DoD medics it is the ADViSOR line – ADvanced VIrtual Support for OpeRational Forces) rather than handling it on your own.
Now, if it is pneumonia and you start the antibiotics right away, you’ve got a high chance of seeing your patient improving quickly and keeping him on your team (no evacuation necessary). On the other hand, if you and your consultant determine your patient is likely to have a PE, then he needs anticoagulation and evacuation. As a SOF operator on therapeutic anticoagulation you are pretty much useless to your deployed team.
Ever seen a “little” nosebleed in a Gruntpa on warfarin or other “blood thinner” for that matter? Now imagine getting shot at while taking those meds!
SONOGRAPHiC MiSSiON SUPPORT
As always SOFsono comes to your rescue! Grab whatever probe you have – start with phased array or curvilinear if you can, for the big picture, and place it where it hurts! So simple is that! Here it is the same view as the RUQ of your eFAST, just that you slide it up North, towards the head, so that you can focus on the thoracic cavity content.
The first thing you notice is the spine shadow extending above the diaphragm. You surely know it is abnormal. Air-filled lungs would not let you see the thoracic spine. This is only possible if you have a pleural effusion and/or parenchymal consolidation, that is MORE fluid and LESS air in the alveoli.
The second thing that catches your eye is this liver-like appearance of the lung parenchyma. Hence the term hepatization to describe this pulmonary consolidation. Nope, it is not a mirror image artifact. If it was, you would not be able to see the thoracic spine.
All those bright white linear, branching or lense-shaped echogenic structures within the consolidation represent sonographic air bronchograms. The alveoli are flooded and now you get to see the gas-filled bronchi.
Now look what happens when you watch this consolidation on a video clip!
How convenient – we just caught a dynamic air bronchogram. There has to be some ventilation going on since the gas is moving within the bronchi, so it can’t be atelectasis. In a clinical scenario like ours (fever, cough…) it is pretty much pathognomonic for pneumonia !
Of course there are other less specific sonographic signs suggestive for pneumonia. We will make sure to cover them at some later time. Altogether, ultrasound scores really well, far better than chest x-ray when it comes to diagnosis of pneumonia .
- CDC Blood Clots and Travel: What You Need To Know.
- Lapostolle F et al. Severe Pulmonary Embolism Associated with Air Travel. N Engl J Med 2001; 345: 779-783.
- Lichtenstein D et al. The dynamic air bronchogram. A lung ultrasound sign of alveolar consolidation ruling out atelectasis.Chest. 2009; 135: 1421-1425.
- Chavez MA et al. Lung ultrasound for the diagnosis of pneumonia in adults: a systematic review and meta-analysis.