systematic approach to reading CXR and hidden pneumonias

For this pearl of the day we will talk about systematic approach to reading CXR and hidden pneumonias:

The key is to be very systematic when approaching CXRs and that is what radiologists do each time.

Here is the suggested approach by the Brown EM program (https://brownemblog.com/?offset=1533674064239&category=Education)

https://commons.wikimedia.org/wiki/File:Mediastinal_structures_on_chest_X-ray.svg#/media/File:Mediastinal_structures_on_chest_X-ray,_annotated.jpg

When ready to review the x-ray, consider the commonly used “A, B, C, D, E, F” system.

A - Airway- trachea, carina, right and left main bronchi

B - Bones and soft tissue- clavicles, ribs- posterior and anterior, vertebral bodies, and sternum on lateral films. Look for any fractures, dislocations, or lytic lesions.

C - Cardiac- cardiac silhouette and mediastinum. The cardiac silhouette should be less than half of the thoracic cavity. AP films exaggerate heart size, so this rule does not apply. Assess the borders of the heart and the hilar structures

D - Diaphragm- right should be higher than left and you should see a gastric air bubble on the left. Is there any free air under the diaphragm? Evaluate the costophrenic angle and pleura (normally invisible due to thinness).

E - Everything else (lines and tubes, pacemakers, artificial valves)

F - Fields- FINALLY, evaluate the lung fields. Lungs are the area of greatest interest, so it is helpful to keep this at the end to prevent distraction. Divide each lung into three “zones” when reading a chest x-ray. These do not correlate with the lobes. Remember, there are 2 lobes on the left (upper and lower) and 3 on the right (upper, middle and lower). 

Hidden pneumonias:

Go through your ABCDEFs and look at the signs of hidden pneumonias:

Silhouette sign

The loss of the normal silhouette of a structure is called the silhouette sign.  - It enables us to find subtle pathology and to locate it within the chest.

R middle lobe pneumonia

LLL pneumonia

LLL pneumonia

Hidden areas

There are some areas that need special attention, because pathology in these areas can easily be overlooked:

apical zones

hilar zones

retrocardial zone

zone below the dome of diaphragm

These areas are also known as the hidden areas.

But in doubt get another view or a chest CT.

References:

https://brownemblog.com/?offset=1533674064239&category=Education

http://www.radiologyassistant.nl/en/p497b2a265d96d/chest-x-ray-basic-interpretation.html#in5145a34e91e18

https://www.bir.org.uk/media/258608/mark_rodriguez_-_philips_trainee_for_excellence_-_unofficial_guide_to_radiology.pdf

POTD: Pulmonary Embolism Decision Rules - Beyond the Basics

Special thanks to Dr. Errel Khordipour for giving this amazing review and Dr. Anna Bona for taking meticulous notes during this talk!

TL;DR

• PE carries an 8% 30-day mortality after diagnosis (some studies higher)

• CTA has a very high false positive rate

• Step 1: based on the patient's history and presentation, do you think the patient has a PE? If yes, proceed. If no, STOP

  • Read more below for nuances re: features that makes a patient risky for PE

• Step 2: Using your clinical decision rules (Well's, Geneva, or clinical gestalt), is the patient low, medium, or high risk?

  • Low risk: PERC

  • Medium: D-dimer --> then CTA if positive

    • Age adjust your d-dimer if possible

  • High Risk: CTA

• Step 3: Treat! (or don't treat!)

  • Unstable --> tPA and MICU

  • Stable --> get labs, echo

    • Labs abnormal or echo w/ RV strain --> heparin +/- half-tPA

    • Labs/echo normal --> determine the pt's PESI score

      • High --> heparin

      • Low --> lovenox and discharge

• Subsegmental PEs in patients < 50 with stable vitals have a very low risk of adverse outcome

  • May consider discharging without anticoagulation if no DVT is present and there are no risk factors for recurrence

• If the study is inadequate, refer to the d-dimer

  • If d-dimer positive, get bilateral lower extremity dopplers

    • Discharge if negative

    • If positive, consider anticoagulation based on risk factors and labs and f/u with PMD for repeat doppler in 3-7 days. 

Interested? Let's get more specific!

Let’s consider a patient that rolls into your emergency department. They’re complaining of chest pain and shortness of breath. You’re working with a medical student and they list pulmonary embolism as a differential diagnosis. How do we risk stratify our patients using our decision making tools.

Background
First off, why do we care? First off, PE is a very much-feared missed diagnosis, which carries an 8% 30-day mortality** after diagnosis (this was much lower than I expected, to put this into context, hemorrhagic strokes carry a 25-40% mortality depending on your source and hip fractures carry a 4-10% mortality rate depending on your source).

**some studies show a 30% mortality, however those were autopsy studies, so it is unknown whether the patients died with a PE or as a result of a PE.

That being said, our testing methods are very much imperfect! The false positive rate on CTA for segmental PE is 25% and even scarier, the false positive rate for subsegmental PEs is 60%!! Not a great test! Plus, a CTA is not a benign test. Contrast can cause anaphylactoid reactions and lifetime risk of malignancy increases with each CT. Plus, once a patient is labeled as having a PE (even subsegmental), they’re much more likely to get scanned in the future.

So let’s talk about how we can determine who is high risk and who is low risk.

Step 1: Consider the patient’s presentation and history

Vital signs:

Risk Factors: 

Prior VTE (PE/DVT): Was the last PE/DVT unprovoked or provoked? More concerning if the last PE/DVT was unprovoked (e.g. the patient was not immobilized for a long period of time). This does not change if testing for hypercoagulability was negative. If provoked, this is less concerning.

Malignancy History: Higher risk with active cancer. This either means active treatment within the last 6 months or metastatic disease. Chemotherapy patients are also more at risk. Not all malignancies are created equal, though! Your risk is even higher with pancreatic cancer, multiple myeloma, colon cancer, glioblastoma, and melanoma.

Immobility: certain types of immobility are higher risk than others! Examples: patients in casts, hospitalized trauma patients (others not at higher risk). Surgical patients are higher risk if they were intubated, received general anesthesia, or received an epidural (e.g. knee surgery, abdominal surgery, neurological surgery). Being in a continuous seated position for > 6 hours might be a risk factor.

OCPs: estrogen of any form increases risk (e.g. OCPs, estrogen replacement, intra-vaginal estrogen). For transgendered patients, more study is needed to determine increased risk.

Pregnancy: Highest risk 2 weeks postpartum. If a patient is pregnant and symptomatic, they have a 70% risk of PE.

Increased risk at age 50: Risk of PE perpetually increases with age. 

Symptoms:

Chest pain: pleuritic chest pain suggest peripheral PE (65%)

Hemoptysis: more indicative of pulmonary hemorrhage, not infarct

Exertional Dyspnea: concerning! You do not need to have chest pain to have a PE!! There is a syndrome that consists of subacute dyspnea that gets worse over days that is predictive of central PE.

Calf pain/Calf swelling: unilateral calf pain (the symptom) and calf swelling (the physical exam finding) are both concerning.

Syncope: corresponds to a large clot burden, but syncope  (likely does not confer an increased likelihood of PE)

Anticoagulation: if they are compliant with anticoagulation, they are less likely to have PE. While this is definitely true with NOACs, with Coumadin, it’s less certain because levels will vary regardless of compliance with medication. Symptoms that are not significant: orthopnea, palpitations, anxiety, dizziness 

Physical Exam Findings:

Abnormal pulmonary exam - decreases likelihood of PE

Clinical signs of DVT - such as calf swelling, redness, etc. increases likelihood 

STEP 1 (cont): Do you, based on the information above, feel that a PE is possible? Meaning, it is ABOVE the 2% threshold for PE. 

Professional recommendation: if the patient has risk factors in 2 or more of the above categories (e.g. vital sign and risk factors, or risk factors and exam findings), and there is no alternative explanation for the patient's presentation, you can say adequately that you have suspicion for PE. 

If you have less than a 2% clinical suspicion for PE, STOP. You do NOT think there is a PE and you do not evaluate further. I repeat - STOP! Evaluate for other suspected pathologies). ACEP Guidelines: 2% is an acceptable cutoff recognizing limitations of testing and risk of false positives (in latest NSTEMI guidelines) Now that you truly think your differential should include PE...  

STEP 2: RISK STRATIFY

It doesn't matter if you use Well's Score vs. Geneva vs. Gestalt; all have been shown to be equal. Keep in mind these decision tools SHOULD NOT used to rule out. They are only to RISK STRATIFY. Meaning that you clinically have a suspicion of said disease before you use them. This means you should NEVER document "Well's score low, not likely PE". 

 High risk: get a CTA! May consider empiric heparin before or after CTA.  

Moderate: D-dimer. 

• In general, you should use age adjusted cutoffs for patients > 50. The conversion depends on which unit you use. 

  • FEU (fibrinogen unit, cutoff usually ~ 500): add the age x 10

  • DDU (d-dimer unit, cutoff usually ~ 250): add the age x 5

Low: PERC

STEP 3: Further Management

Ever get a reading that said "evaluation for sub-segmental suboptimal due to motion artifact? What do you do? (Only if vital signs are stable)

• Get a d-dimer (if not already obtained)

• Positive --> LE dopplers

  • Yes DVT: anticoagulate!

  • No DVT: discharge with or without anticoagulation based on risk factors and lab values; follow-up with PMD for repeat surveillance ultrasound in 3-7 days. 

• Negative -->  Discharge 

Now let's go over what you do if a PE is found...

Disposition: depends on if the patient is stable or unstable

Unstable: hypotensive, signs of shock, etc

• Give tPa and admit to MICU

Stable: labs (BNP, troponin), echo

• If the patient as abnormal labs or right heart strain, give heparin +/- half-dose tPA and admit to ICU/tele

• If normal, determine the patient's PESI Score

  • High PESI score --> give heparin and admit to floor

  • Low PESI score --> give lovenox** and discharge

** There inadequate evidence and no FDA approval for NOACs at this time
  Subsegmental PEs in patients < 50 with stable vitals have a very low risk of adverse outcome, so you may consider discharging without anticoagulation if no DVT is present and there are no risk factors for recurrence and have the patient f/u with PMD for surveillance of PE symptoms. 

POTD: TB in the ED

Approach to TB in the ED.

TB might be more common than you think: In NY alone, in 2016, 3.9 cases per 100,000 people, 761 cases in NY in 2016.

Reactivation TB is about 90% of active TB in the United States. 

Who is at high risk?

Those with no “usual source of care”

• ethnic minorities

• foreign born

• HIV patient

• drug users

• nursing home patients

• homeless patients

• prisoners

Why is it often missed?

Non-specific presentation of TB

• Cough present: 64%

• Cough was chief complaint: 20%

• Only 36% had respiratory complaint at triage

What to do if for high suspicion of TB:

• Negative pressure isolation room

• N95 fitted masks

• CXR and rapid HIV

  • Why HIV test?

    • HIV increases risk of having reactivation TB

    • Immunosuppression will give you atypical cxr findings

• Looking primarily for active tuberculosis 

Confirmatory testing:

• PPD: Sensitivity 60-100%

• QuantiFERON Gold: Sensitivity 81-96%

• Sputum Looking for AFB on smear (Ziehl-Neelson stain)

  • Variable Sensitivity: 20-60%

  • High specificity: 90-100%

• Culture

  • Slower results: 7days- 8 weeks

  • Gold standard: 99% sensitivity

• Rapid TB testing/ Cepheid Xpert MTB/RIF PCR assay

  • Respiratory for assistance in collection

  • 5 ml specimen

  • Rifampin resistance detection

  • Supposed to be a 2 hr turnaround

  • 2 negative sputum specimens at least 8 hrs apart: can remove from isolation

  • Sensitivity about 75-93%

*This is a sample rule out TB protocol that I adapted from Annals of Emergency Medicine October 2016 : http://www.annemergmed.com/article/S0196-0644(16)30920-9/fulltext