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Point of care ultrasound VS CT pulmonary angiogram in suspected pulmonary embolus

Three Part Question

[In adult patients presenting with clinical suspicion of pulmonary embolus] is [noninvasive, multi-organ point of care ultrasound, when compared to CTPA] specific and sensitive enough [to confirm or refute the presence of pulmonary embolus]?

Clinical Scenario

A 24 yo woman presents to the ED with shortness of breath and pleurisy. She is otherwise healthy and on no medications except the birth control pill for the past year. There are no other clinical signs or symptoms suggestive of DVT and her heart rate is normal. Can I, as an ERP with some training in bedside ultrasound, reliably confirm or refute the diagnosis of a pulmonary embolus using point-of-care ultrasound?

Search Strategy

Pubmed was used for papers of any date to the present (January 2017) – all databases searched.

Google Scholar was used to search for any publications that may have been missed in pubmed.

Pubmed Search: (((((("computed tomography angiography"[MeSH Terms]) OR CT[Text Word])) OR ((((CTPE[Text Word]) OR CTPA[Text Word]) OR CT pulmonary angiogram[Text Word]) OR CT pulmonary embolism[Text Word]))) AND (((("echocardiography"[MeSH Major Topic]) OR ultrasound[Text Word]) OR echo[Text Word]) OR echocardiography[Text Word])) AND (((pulmonary embol*[Text Word]) OR "pulmonary embolism"[MeSH Terms]) OR PE[Text Word])

Google Scholar: Searched for the first 100 results using the terms "ultrasound", "pulmonary embolism”, and "diagnosis”

Search Outcome

614 papers were found on the pubmed search, of which 3 looked specifically at bedside POCUS administered by non-radiologists or technicians. The reference investigation for all 3 papers was always CTPA, and criteria for patient enrollment was also based on Wells criteria calculations and/or d-dimer values. The remaining papers were excluded because of the following reasons:
1. Ultrasound administered by technician or radiologist.
2. Trans-esophageal ultrasound was used.
3. Complex calculations of ultrasound findings requiring expertise beyond that of a minimally trained sonographer to interpret data, not making it a feasible tool in the busy environment of an ED.

93,800 results were found on Google Scholar, no additional papers were identified.

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Nazerian P et al.,
2014,
Italy
Consecutive patients ≥ 18 yo suspected of having a PE were enrolled from June 2012 – November 2012 from the ED of 2 university hospitals, and 1 community hospital in Italy.

Included: Patients had to have a Well’s score >4 or D-dimer ≥ to 500 ng/mL with a CTPA ordered

Excluded: Patients with a Well’s score ≤4 or D-dimer <500 ng/mL
Multicenter prospective accuracy studyPerformance of multi-organ, bedside ultrasound in detecting the presence of a PE measured as sensitivity and specificity compared to CTPA.

Outcomes were reported as Sensitivity and specificities of organ ultrasounds.

POCUS was conducted by 9 ERPs with ultrasound experience, as well as 4 residents, 2 ER and 2 IM. Radiologists whom read the CTPAs were blinded to POCUS results and vice versa.
Total of 357 patients. Results reported with 95% CI in brackets, as well as +LR

Lung: Sens. 60.9% [51.1-70.1], Spec. 95.9% [92.7-98], +15. Heart: Sens. 32.7% [24.1-42.3], Spec. 90.9% [86.6-94.2], +3.6. Vein: Sens. 52.7% [43-62.3], Spec. 97.6% [94.8%-99.1%], +21.7. Multiorgan: Sens. 90% [82.8-94.9], Spec. 86.2% [81.3-90.3], +6.5.

If alternative Dx was seen on multiorgan  Spec. 100%[96.7-100], Sens. 42.9% [36.7-49.3], +1.75.
All ERPs had at least 2 years of training in ultrasound use, which is not generalizable at this time to the population’s skill level in POCUS.

Additionally, the finding of a lower specificity for multi-organ POCUS remains poorly explained in the paper, given that specificity had been quite high in individual organ groups.
Koenig S et al.,
2014,
USA
Study was performed at Long Island Jewish Medical Center in New York, from July 2010 to July 2011. A convenience sample was used (between 0800 and 1800 on weekdays).

Included: Patients ≥18 yo suspected of having a PE with a CTPA ordered by an attending physician.

Excluded: Pregnancy, age <18 yo, and lack of informed consent
Single center observational prospective studyThe aim of this study was to examine whether point-of-care ultrasonography that includes thoracic ultrasonography, goal-directed ECG, and lower extremity DVT study might be useful to reduce the need for CTPA in patients with suspected PE.

3 staff physicians or 3 fellows with critical care ultrasound training conducted POCUS. Results were blinded to both ultrasonographers as well as radiologists reading the CTPA
Total of 96 patients. 54 had ultrasound findings suggestive of another disease process that could explain the symptoms. In all 54 cases, the patient was negative for PE and the CTPA agreed with the alternative diagnosis provided by bedside US. 2 cases had positive DVT findings and were also found to have PE on CTPA. In the remaining 40 scans that did not provide an alternative diagnosis, the ultrasonographers recommended CTPA be performed. 12 of those were found to have a PE.The study used critical care staff and fellows, not specifically ERPs, but still focused on the use of POCUS as a diagnostic modality. Their level of training in POCUS was quite comprehensive as defined by a competence statement on the subject.

The study failed to break down sens/spec per modality and is a big weakness in its utility in comparing different ultrasound techniques.
Shiver SA et al.,
2010
USA
All adult patients undergoing CTA for workup ?PE were candidates. Convenience sample only, candidates were chosen when 1 of 4 ERPs were on shift. Single center, prospective studyThe aim of this study was to compare ERP–performed ultrasound (EPPU) of the lower extremities with CT venography (CTV) in emergency department (ED) patients undergoing workup for pulmonary embolism (PE).

4 ERPs were the sonographers, 2 of which had no formal ultrasound training. Results were blinded to both radiologists and the ERPs.
Total of 61 patients. EPPU found 55 negative and 6 positive scans. CTV found 54 negative and 7 positive scan, and the only positive scan it found that EPPU didn’t see was a proximal iliac vein thrombus. CTPA had a total of 11 positive findings and agreed with all positive findings from EPPU and CTV.

When comparing EPPU to CTV for diagnosing PE, sens was 86% [42%-99%] and spec. 100% [91%-100%]
The study used specifically ERPs however, only compared leg ultrasound as their POCUS test in diagnosing PE.

Additionally, the ERPs in the study were quite experienced,

This is an earlier study, and it appears multi-organ POCUS has only really become a research interest as of 2014.

Comment(s)

The diagnosis and evaluation of patients presenting with shortness of breath has always been a challenge in the busy environment of an emergency department. Numerous evidence-based approaches have been developed over the years to aid the clinician in risk stratifying patients based on clinical symptoms and history. However, the reference test to diagnose a PE remains CTPA, which holds with it some potential harm to the patient. It is a fair amount of radiation as well as even contraindicated in certain patient populations. Ultrasound provides a non-invasive diagnostic tool with virtually no harm or risk to the patient. The fact that more and more emergency medicine residents and staff physicians are being trained on the use of ultrasound makes it an even more attractive diagnostic modality.

There have been numerous publications on the use of ultrasound to help with the diagnosis of PE. However, only recently has there been a focus on a multi-organ approach by the physician at the bedside. The interpretation of data gathered by these ultrasound techniques is also simple enough that a non-radiologist or non-technician is able to make use of the information. From a thorough publication search strategy, 2 papers were found that examined specifically the multi-organ POCUS approach and its diagnostic power. There was also another paper that looked only at leg vein POCUS, but is one of the few that actually used ERPs as the ultrasonographers and explored the role of POCUS in determining patient risk in having a PE. Thus, it was also included in this analysis.

The three papers reviewed show that the ability for bedside POCUS to rule out PE in the absence of findings is rather poor. However, positive findings were shown to have a strong predictive value in diagnosing either PE or alternative diagnosis, if present. The two multi-organ trials agree that sensitivity is quite high for any positive findings in multi-organ POCUS (90% [82.8-94.9] in Nazerian et al., and approaches 100% for Koenig et al.). Additionally, the specificity for POCUS to predict an alternative diagnosis to explain patient symptoms was virtually 100% for both studies. The CTV vs EPPU study also helped reinforce the utility of POCUS when positive findings were present. When compared to CTV, the sensitivity and specificity of an ERP conducted leg vein POCUS was 86% [42%-99%] and 100% [91%-100%] respectively.

Editor Comment

POCUS, Point-of-care ultrasound; CTV, CT venography; EPPU, Emergency physician performed ultrasound; CTPA, CT pulmonary angiography; ERP, Emergency room physician; ED, Emergency department

KMJ Keeper

Clinical Bottom Line

The ability of a multi-organ POCUS approach to help risk stratify patients with clinical signs and symptoms of PE appears very promising. There are only two large studies so far that specifically look at the multi-organ approach, but there are also other studies that look at the diagnostic accuracy of ERP conducted POCUS for specific organ systems, such as leg veins. As previously mentioned, in all studies positive findings in any organ system are almost always diagnostic for either an alternative diagnosis or for PE. This can help avoid the overuse of CTPA in the ED as well as help serve as yet another diagnostic tool to help physicians determine the risk and benefit of treatment in patients who have contraindications for CTPA. However, the overall sample size remains relatively small, and more data is needed to make a definitive statement regarding validity and clinical practice recommendations.

References

  1. Nazerian P, Vanni S, Volpicelli G et al. Accuracy of Point-of-Care Multiorgan Ultrasonography for the Diagnosis of Pulmonary Embolism. Chest 2014:145(5):950–957.
  2. Koenig S, Chandra S, Alaverdian A et al. Ultrasound Assessment of Pulmonary Embolism in Patients Receiving CT Pulmonary Angiography. Chest 2014:145(4):818–823.
  3. Shiver SA, Lyon M, Blaivas M et al. Prospective comparison of emergency physician–performed venous ultrasound and CT venography for deep venous thrombosis. The American Journal of Emergency Medicine; 2010: 28:354-358.