Comparison of Four Views to Single-View Ultrasound Protocols to Identify Clinically Significant Pneumothorax

Background

Ultrasound has become a key adjunct for the initial evaluation of trauma patients in the emergency department (ED), with the eFAST, or extended focused assessment with sonography in trauma examination, including lung evaluation for the presence of a pneumothorax (PTX) or hemothorax. While prior research has shown ultrasound (US) to be very effective at identifying a PTX [1], there is no standardized imaging protocol that has been shown be superior to others. The two most common approaches are a single view of each hemithorax and four views of each hemithorax [2] —this paper sets out to determine if the single view strategy is sufficient to identify a clinically significant PTX.

Comparison of Four Views to Single-view Ultrasound Protocols to Identify Clinically Significant Pneumothorax

 

Clinical Question

Does the single-view or four-view lung US technique have a higher diagnostic accuracy for the identification of clinically significant PTX in trauma patients?

Methods & Study Design

  • Population
    • The study was conducted at a single urban academic ED with an annual volume of 130,000 patients and a dedicated Level I trauma service staffed by trauma surgeons and EM physicians. Adult patients with acute traumatic injury who were undergoing a CT scan of the chest as part of their clinical care were eligible for enrollment.
  • Intervention
    • Patients were assigned to one of two imaging protocols, a single view of each hemithorax or four views of each hemithorax prior to any CT imaging being done, with US images obtained by emergency physicians or the attending trauma surgeon using a 7.5-Mhz (5- to 10-MHz) linear array transducer. US exams were performed by both residents and attending physicians who had been credentialed in both US protocols.
  • Outcomes
    • Researchers looked for the ability of US to identify clinically significant PTX requiring chest tube placement; a PTX was considered clinically insignificant if the radiologist, who was blinded to the US interpretation, read the CT scan as a thin collection of air up to 1 cm thick in the greatest slice or seen on fewer than five contiguous slices.
  • Design
    • This was a randomized, prospective trial on trauma patients.
  • Excluded
    • The study excluded any patient who was too unstable and required clinical care that prevented performing a chest wall US, patients with a chest tube in place prior to arrival, children, pregnant women, and prisoners.

Results

    • For clinically significant PTX, CXR showed a sensitivity of 48.0% and specificity of 100%, a single view US showed a sensitivity of 93.0% and a specificity of 99.2%, and four views showed a sensitivity of 93.3% and specificity of 98.0%. There was no statistically significant difference in either sensitivity or specificity when comparing single view and four-view for clinically significant or any PTX.

Strengths & Limitations

  • Strengths
    • Randomized, prospective trial
    • 100% agreement between the initial US read by the performing provider and the study author, for a Cohen’s kappa of 1
  • Limitations
    • Study was conducted at a single center with a limited number of US operators
    • Standard prehospital approach to spinal immobilization that results in placement of patients supine on a long board - in areas where this approach may differ (e.g., patients arrive semirecumbent or upright), the positioning of a PTX in the chest may be altered, rendering a single view of the anterior chest wall less accurate
    • As this study was a convenience sample that required the treating physician to remember to enroll the patient and randomize them prior to performing the US, there is a possibility of selection bias

Author's Conclusions

"The sensitivities are equivalent for both a single view and four views of each hemithorax when using point-of-care ultrasound to evaluate for a clinically significant pneumothorax in the trauma population.  The additional time required for additional views should be weighed against the lack of additional diagnostic accuracy when evaluating critically ill and time-sensitive trauma patients in the ED."

Our Conclusions

Although not all PTXs are located anteriorly and multiple views of each hemithorax may be thought to maximize sensitivity and/or allow the physician to be able to attempt to quantify the size of the PTX, performing eight views instead of two views during the eFAST requires extra time while adding no diagnostic value.  From this study, it appears that a single view on each side of the thorax is sufficient to detect clinically significant PTXs on trauma patients.

As with any diagnostic tool, it is important to remember its limitations. Specifically, the US exams in this study were done in supine patients, who were brought in by EMS in a supine position, allowing the pneumothorax to move to the most anterior portion of the chest. Caution should be taken when applying the test characteristics of this study to patients that are not in the supine position. There was also one patient who had a significant PTX that was missed by US and required a chest tube. This patient had received a needle decompression by prehospital providers and was randomized to a single anterior US chest view that was performed just lateral to the needle insertion site which may have led to false negative US exam. It appears this specific group of patients may benefit from a more comprehensive four-view lung examination.

 

The Bottom Line

A single anterior view on each side of the chest in a supine patient is sufficient to detect clinically significant pneumothoraces.

Authors

This post was written by Ben Foorman, MS4 at UCSF. It was edited by Michael Macias, MD.

References

    1. Lichtenstein DA, e. (2017). Ultrasound diagnosis of occult pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/15942336
    2. Blaivas M, e. (2017). A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/16141018
    3. Helland G, e. (2017). Comparison of Four Views to Single-view Ultrasound Protocols to Identify Clinically Significant Pneumothorax. - PubMed - NCBI . Ncbi.nlm.nih.gov. Retrieved 28 July 2017, from https://www.ncbi.nlm.nih.gov/pubmed/27428394

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