Opening Pandora’s box: the potential benefit of the expanded FAST exam is partially confounded by the unknowns regarding the significance of the occult pneumothorax

Abstract

Introduction Point of care (POC) ultrasound brings another powerful dimension to the physical examination of the critically ill. A contemporary challenge for all care providers, however, is how to best incorporate ultrasound into contemporary algorithms of care. When POC ultrasound corroborates pre-examination clinical suspicion, incorporation of the findings into decision-making is easier. When POC ultrasound generates new or unexpected findings, decision-making may be more difficult, especially with conditions that were previously not appreciated with older diagnostic technologies. Pneumothoraces (PTXs), previously seen only on computed tomography and not on supine chest radiographs known as occult pneumothoraces (OPTXs), which are now increasingly appreciated on POC ultrasound, are such an example.Methods The relevant literature concerning POC ultrasound and PTXs was reviewed after an electronic search using PubMed supplemented by ongoing research by the Canadian Trauma Trials Collaborative of the Trauma Association of Canada. Results OPTXs are frequently encountered in the critically injured who often require mechanical ventilation with positive pressure breathing (PPB). Standard recommendations for post-traumatic PTXs and the setting of PPB mandate chest drainage, recognizing a significant rate of complications related to this procedure itself. Whether these standard recommendations generated in response to obvious overt PTXs apply to these more subtle OPTXs is currently unknown, and evidence-based recommendations regarding appropriate therapy are impossible due to the lack of clinical studies. Conclusions OPTXs are a condition that illustrates how incorporation of POC ultrasound findings brings further responsibilities to critically appraise the significance of these findings in terms of patient outcomes and overall care. Adequately powered and adequately followed-up clinical trials addressing the treatment are required.Keywords Point of care ultrasound Á Critical ultrasound Á Pneumothorax Á Occult pneumothorax Á Critical care Á Mechanical ventilation Electronic supplementary material The online version of this article (

Portable bedside ultrasound: the visual stethoscope of the 21st century

“…In the setting of trauma, the literature reveals that bedside ultrasound has sensitivity for pneumothorax that far exceeds the sensitivity of a chest xray [ 3 , 9 , 18 , 38 - 40 ]. As a result, small, formerly "occult" pneumothoracies are now being discovered which previously may have gone untreated, with no detriment to the patient [ 42 ]. Using ultrasound to quantify the size of the pneumothorax may help avoid unnecessary interventions [ 3 ].…”

The sonographic diagnosis of pneumothorax

“…[ 1 ] While further studies on the management of OPTXs are pending, we encourage physicians to incorporate this diagnostic tool in the evaluation of patients, but recommend diligence and clinical correlation in interpreting the significance of the results. [ 3 ]…”

“…[ 1 ] While the optimal management of these OPTXs is still a matter of debate,[ 1 2 ] all agree that thoracic US provides a method of rapidly detecting PTXs that would have been missed if only supine CXRs were obtained or diagnosed in a delayed fashion if CT scans were obtained in all patients. [ 3 ] Thoracic US possesses the advantages of portability, repeatability, absence of radiation, ease of use and high sensitivity in the detection of PTX. [ 4 ] A growing number of publications now support its use as part of the initial assessment of the trauma patient in combination with the FAST exam, giving rise to the term EFAST: The extended focused assessment with sonography for trauma.…”

“…Lung sliding (LS) being a dynamic process requiring real-time imaging and real-time interpretation, the color power doppler function allows a single still image to depict this dynamic process. [ 3 8 ] When evaluating normal lung without a pneumothorax, there will be a flow signal at the thoracopleural interface corresponding to the sliding movement of the visceral and parietal pleura. M-mode, which displays motion of anatomical structures in time, also enables the evaluator to depict LS as a static image.…”

Conservative management of occult pneumothorax in mechanically ventilated patients: A systematic review and meta-analysis

“…13 It is not as sensitive or specific as CT scans, however it has the benefit of being a rapid, clinician performed, bedside test. 60…”