Anatomical mapping of traumatic pneumothoraces missed by prehospital ultrasonography - a retrospective cohort study.

Objective: Prehospital performed Extended Focused Assessment with Sonography in Trauma (EFAST) has poor sensitivity for pneumothorax (PTX) when compared to scans performed in hospital. This study describes the computed tomography (CT) location of PTX detected after an initial negative prehospital EFAST.

Methods: Trauma patients treated by New South Wales Ambulance (Aeromedical Operations) who underwent prehospital EFAST between 1^st August 2022 and 31^st December 2023 were included if they were found to have PTX on CT imaging following a negative or indeterminate prehospital EFAST ultrasound. Patients were excluded if prehospital pleural decompression was undertaken. Corresponding CT imaging was manually analysed for the location of each PTX and mapped to two-dimensional coordinates on an unfurled thoracic cage.

Results: Of 58 patients median (IQR) age was 29 (20, 58) years. The majority (76 %) were male who had sustained blunt trauma. The median (IQR) estimated PTX volume was 8 % (4-10) with 43 % of patients having a pneumothorax located to either the second intercostal space or most anterior portion of the chest on CT-mapping. The midpoints of each locule were anatomically distributed with a median (IQR) of 4^th (3^rd-5^th) intercostal space and distance from the sternal edge (cm) of 4.1 (2.5-5.1) on the right, and 4.4 (3.5-5.2) on the left. Most PTX were sonographically occult due to apical, retrosternal, or posterior position.

Conclusion: Most traumatic PTX missed by prehospital EFAST were truly sonographically occult, but a significant number corresponded with the traditional scanning landmarks, particularly the parasternal 4^th intercostal space. This reinforces current literature advocating this scanning region. The balance between optimal detection and sono-paralysis should be considered for ongoing education and governance.