SGEM#276: FOCUS on PE in Patients with Abnormal Vital Signs

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Date: November 21st, 2019

Reference: Daley et al. Increased Sensitivity of Focused Cardiac Ultrasound for Pulmonary Embolism in Emergency Department Patients With Abnormal Vital Signs. AEM November 2019

Guest Skeptic: Dr. Corey Heitz is an emergency physician in Roanoke, Virginia. He is also the CME editor for Academic Emergency Medicine.

Case: You are caring for a 45-year-old male patient in the emergency department with pleuritic chest pain. You suspect he has a pulmonary embolism (PE), and the CT scanner is currently being used up by a multi-patient multiple-trauma pan-scan which promises to take hours. Your patient has a heart rate of 105 bpm and a systolic blood pressure of 95 mmHg. You pull the department’s ultrasound machine to the bedside and prepare to do a focused cardiac ultrasound to decide if you want to treat for a PE while waiting for the scanner to free up.

Background: We have covered the issue of PE many times on the SGEM. This has included outpatient management (SGEM#51 and SGEM#126), catheter directed thrombolysis (SGEM#163) and even discussed the PERC rule with its creator, Dr. Jeff Kline (SGEM#219).

We may have covered it so often because PE is commonly suspected in patients presenting the ED with chest pain, shortness of breath, or other symptoms. The current gold standard test is a CT angiogram of the pulmonary arteries (CTA), but this test cannot be performed immediately in some patients due to renal function, availability of the equipment, or contrast allergies.

There are concerns about doing CTAs in pregnant patients due to the radiation exposure to both the mother and fetus. We have a show coming up soon looking at a pregnancy adapted YEARS criteria to help minimize the number of CTAs ordered in this patient population.

In addition, patients with hemodynamic instability may not be appropriate to take out of the resuscitation bay. Focused cardiac ultrasound (FOCUS) can show findings of right ventricular strain caused by a PE, but in all patients suspected of PE, it is relatively insensitive. However, it has been suggested that in patients with hemodynamic instability, the sensitivity may be higher.

Clinical Question: In patients presenting to the ED with suspected PE, who have abnormal vital signs, what is the sensitivity of FOCUS for PE?

Reference: Daley et al. Increased Sensitivity of Focused Cardiac Ultrasound for Pulmonary Embolism in Emergency Department Patients With Abnormal Vital Signs. AEM November 2019

Population: Adult patients (>17 years old) undergoing evaluation for PE who are tachycardic (HR >100bpm) and/or hypotensive (systolic BP <90mmHg)
- Excluded: Prisoners, wards of the state, non–English-speaking patients, and those where investigators could not obtain any ECHO data due to technical challenges.
Intervention: Focused cardiac ultrasound (FOCUS)
Comparison: CT angiography of the pulmonary arteries
Outcome:
- Primary Outcomes: Sensitivity of FOCUS for PE patient with a HR ≥ 100 beats/min or sBP < 90 mm Hg (n = 136) and those with a HR ≥ 110 beats/min (n = 98).
- Secondary Outcomes: Specificity and likelihood ratios of FOCUS for PE in each population.

Dr. James Daley

This is an SGEMHOP episode which means we have the lead author on the show. Dr. James Daley is an emergency physician at Yale New Haven Hospital where he’s currently finishing up a fellowship in emergency ultrasound and research. His work centers around the use of point of care echocardiography in the diagnosis of pulmonary embolism and he hopes to branch out to other topics in resuscitation research in the future.

Authors’ Conclusions: “A negative FOCUS exam may significantly lower the likelihood of the diagnosis of PE in most patients who are suspected of PE and have abnormal vital signs. This was especially true in those patients with a HR ≥ 110 BPM. Our results suggest that FOCUS can be an important tool in the initial evaluation of ED patients with suspected PE and abnormal vital signs.”

Quality Checklist for Observational Study:

Did the study address a clearly focused issue? Yes
Did the authors use an appropriate method to answer their question? Unsure
Was the cohort recruited in an acceptable way? No
Was the exposure accurately measured to minimize bias? Yes
Was the outcome accurately measured to minimize bias? Yes
Have the authors identified all-important confounding factors? No
Was the follow up of subjects complete enough? Yes
How precise are the results? Not very precise
Do you believe the results? Yes
Can the results be applied to the local population? Unsure
Do the results of this study fit with other available evidence? Yes

Key Results: They screened 143 patients who underwent CTA with 136 subjects enrolled in the study. The mean age was in the mid-50’s, 59% were female, 23% had a previous VTE, 40% had cancer in the previous 6 months and 15% had signs or symptoms of a DVT.

FOCUS had a sensitivity of 92% and specificity of 64% for PE

Primary Outcomes:
- Sensitivity of FOCUS for PE in all patient with a HR ≥ 100 beats/min or sBP < 90 mm Hg was 92% (95%CI; 78% to – 98%)
- Sensitivity of FOCUS for PE in patients with a HR ≥ 110 beats/min (n = 98) was 100% (95%CI; 88% to 100%)
Secondary Outcomes:

There was substantial interobserver agreement for FOCUS (kappa = 1.0, 95% CI = 0.31 to 1.0) when they were only required to call it positive or negative.

You can listen to the podcast on iTunes or Google Play to hear James’ answers to our ten nerdy questions.

1. Convenience Sample: This was a convenience sample. We always like to see consecutive patients recruited but understand the reality of research. Do you think this could have impacted the results in any meaningful way?

2. Spectrum Bias: Sensitivity depends on the spectrum of disease, while specificity depends on the spectrum of non-disease. Because they looked at sicker patients (tachycardic and hypotensive) this could falsely raise the sensitivity of FOCUS. Did you consider doing a multivariable model which could have told us what the association of these vital signs with PE are and not have had to prespecify arbitrary cut points?

3. Blinding: The clinicians obtaining the images (staff, residents and medical students) were not blinded to the hypothesis. There are some subjective aspects to FOCUS when obtaining images. In addition, investigators we unblinded to the results in two cases because the patient were getting a heparin infusion when FOCUS was performed. These things could have biased the operators and made the diagnostic parameters look better than if they did not know the purpose of the study or that the patients had a PE.

4. Primary Outcome: You have what seems to be two primary outcomes, meaning the sensitivity in two patient groups. Can you explain the decision not to define one as the primary and the other as a secondary?

5.Missing Data: How researchers handle missing data is important. There were times when data was missing. Can you explain how that could impact your results?

6. Precision: There were fairly wide 95% confidence intervals around the point estimates for the primary outcome. The lower limits of your sensitivity calculations in patients with HR >100 or BP <90 mmHg are in the 70s. How does this affect your recommendation for using FOCUS to evaluate for PE in these patients?

7. Sensitivity and Specificity: While these statistics provide additional information using likelihood ratios can be more helpful to clinicians. We like to see LR+ more than 10 to confidently rule in a condition and LR- less than 0.1 to rule out a condition. FOCUS did not demonstrate robust enough diagnostic accuracy to help make clinical decisions.

8. Inter-Rater Reliability: Your study had seven ultrasound trained attendings, three EM residents and three medical students. All had different degrees of experience. The inter-rater reliability for FOCUS being positive or negative by two separate sonographers was substantial with a kappa statistic of 1.0 (95% CI = 0.31 to 1.0). How did the attendings compare to the residents and medical students?

9. Resource Poor Facilities: You hypothesized in the discussion that FOCUS could play a role in rural locations that lack access to CTA. I have worked my entire career in locations without a CT scanner. Those locations without a CT do not have a high volume of patients presenting with a suspected PE. Would this not make it difficult to maintain FOCUS skills and lower the diagnostic accuracy of this test?

10. Anything Else: Any other thoughts or comments you think the SGEM audience needs to know about your study? Have you considered a head to head comparison of FOCUS vs. CT for PE?

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We generally agree with the authors’ conclusions especially since they used the word “may” which can also mean “may not”.

SGEM Bottom Line: Focused cardiac ultrasound does not have good enough diagnostic accuracy even in patients with abnormal vital signs to safely rule in or rule out PE.

Case Resolution: Your FOCUS exam on your patient shows an essentially normal RV. You delay anticoagulation therapy at this time, choosing to await the CTA results.

We face this all the time with patients needing to be transported to another facility for the CTA. This typically takes about three hours. It is my routine not to anticoagulated prior to transportation.

Dr. Corey Heitz

Clinical Application: In patients with abnormal vital signs, bedside FOCUS may help guide empiric therapy in patients with suspected PE but cannot make a definitive diagnosis to rule in or out a PE.

What Do I Tell My Patient? The ultrasound I just performed tells me that you likely do not have a pulmonary embolism, and I think it’s too risky to provide anticoagulation at this time. Once the CTA results are back, we can decide on definitive therapy.

Keener Kontest: Last weeks’ winner was Ashley Wicks a student paramedic from the UK. She knew the Celsius scale which was invented by Swedish Astronomer Anders Celsius was adopted by an international conference on weights and measures in 1948.

Listen to the podcast to hear this weeks’ trivia question. If you know the answer, send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

SGEMHOP: Now it is your turn SGEMers. What do you think of this episode on FOCUS for diagnosing PEs? Tweet your comments using #SGEMHOP. What questions do you have for James and his team? Ask them on the SGEM blog. The best social media feedback will be published in AEM.

Also, don’t forget, those of you who are subscribers to Academic Emergency Medicine can head over to the AEM home page to get CME credit for this podcast and article. We will put the process on the SGEM blog: