M-mode ultrasound for the detection of pneumothorax during helicopter transport

Background: The presence of the sonographic sliding lung sign (SLS) is a sensitive indicator for the absence of a pneumothorax. The addition of M-mode ultrasound (US) can be a useful adjunct in detecting the SLS. Objective: The objective of this study is to determine the feasibility of using M-mode US in evaluating the SLS during helicopter transport. Methods: A model simulating human lung was used during image acquisition. M-mode images of the SLS were obtained during 3 distinct phases of transport: without rotor rotation, with rotor rotation while on the ground, and at level flight. Four US-credentialed emergency physicians evaluated M-mode US tracings of the model along with examples from human lungs, both with and without pneumothorax, in random fashion. Results: A total of 104 images were reviewed (26 images per reviewer). All of the M-mode images were correctly identified. Motion artifact was noted on the M-mode tracings taken during rotor rotation, which was greatest during level flight. The rotor artifact was not felt to affect the diagnostic utility of the M-mode US tracing. Conclusion: M-mode US may be used successfully to detect the SLS during helicopter transport.