Not so FAST! POCUS vs CXR – A Rebuttal Letter

Written by Aaron Lacy

Spoon Feed
recent publication, cheekily titled Not so FAST – Chest ultrasound underdiagnoses traumatic pneumothorax, concluded ultrasound for traumatic pneumothorax (PTX) should be considered with caution. This response letter breaks down the main reasons why this article is likely a red herring.

Why does this matter?
Swift cavitary triage of multisystem trauma patients is crucial to their subsequent morbidity and mortality. While traditionally done with a systematic physical exam and adjunctive plain x-rays, the rise of POCUS has been revolutionary in evaluation of these patients. There is copious literature supporting the use of POCUS in the diagnosis of traumatic PTX over CXR. However, a recent study claimed that in their shop, CXR was the superior diagnostic tool. What gives? Are we wrong about POCUS?

A FAST and furious response
POCUS is part of the ATLS algorithm and is endorsed by both major trauma associations. This response letter points out several issues with the aforementioned methodology and conclusions by Santorelli et al. Their main arguments include:

  1. Given that only patients with confirmed PTX on subsequent imaging were included in the study, instead of all patients with suspected PTX, it was not possible to meet the Standards for Reporting of Diagnostic Accuracy Studies, STARD guidelines. Because of this, the study cannot accurately assess measures of diagnostic accuracy, like sensitivity, specificity, positive and negative likelihood ratios, etc.
  2. The study lacks generalizability, as it was retrospective, single center, and had sonographers performing EFAST instead of the traditional trauma or emergency physician. While the authors state that their study represents a ‘true evaluation’ of lung ultrasound sensitivity, sonographers and radiologists don’t usually perform/interpret lung POCUS; that’s what emergency and trauma physicians do.
  3. While not specified for lung ultrasound, the rest of the FAST scans were performed with either a phased array or curvilinear probe (set to 2.5-5 MHz), so the lung exam likely was as well. This is not the probe of choice for diagnosing traumatic PTX; instead, the high frequency linear probe would be more appropriate.
  4. This study conflicts with extensive prior literature on the topic, including a Cochrane review. Previous literature shows higher sensitivity and specificity for lung ultrasound in the identification of traumatic PTX over supine CXR. Differences in methodology are likely the cause of the contrasting results in Santorelli et al.

Research is hard to do and hard to get perfect. There is a litany of information hitting the web every day, with an assortment of conclusions and variety of quality. This study does raise some hypothesis generating questions, including the potential role of sonographers and real-time radiology interpretation of sonography in trauma, and these should be explored. However, at this time, I agree with the authors of this response letter: It was likely too much to claim that use of POCUS in lung trauma should be cautioned against in favor of a supine CXR.

Source
Daniel J Kim, Nik Theyyunni, Rachel B Liu Ultrasound is superior to supine chest x-ray for the diagnosis of clinically relevant traumatic pneumothorax. J Trauma Acute Care Surg. 2022 Mar 14. doi: 10.1097/TA.0000000000003575. Online ahead of print.

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