Transcranial Ultrasound in the Helicopter Emergency Medical Services-A Feasibility Study

Transcranial color-coded Doppler (TCCD) is a noninvasive, widely available diagnostic method that may identify large vessel occlusion (LVO) in acute stroke patients. This study aimed to explore whether helicopter emergency medical services (HEMS) physicians could use TCCD in a prehospital setting to identify the proximal segment of the middle cerebral artery (M1-MCA).

In a feasibility study following brief training, three HEMS physicians and a single-reference examiner performed transtemporal TCCD examinations of four healthy volunteers, on ground and in flight a cruising helicopter. One color and one pulsed-wave Doppler image of M1-MCA were stored per examination, and time was recorded. TCCD images were retrospectively assessed by two raters for M1-MCA identification success and image quality, using a 5-point Likert scale.

Participants performed a total of 32 bilateral M1-MCA examinations. The HEMS physicians identified M1-MCA in 83% of color Doppler examinations, with median (interquartile range [IQR]) time of 83 (63-130) s. Substantial inter-examiner variability was observed. The single-reference examiner identified M1-MCA in 88% of color Doppler examinations using 58 (49-101) s. Median (IQR) Likert scores for successful images were high: HEMS physicians 4.5 (4.5-5.0) and single-reference examiner 5.0 (4.5-5.0), with no significant difference between on-ground and in-flight examinations.

Following brief training, HEMS physicians were able to perform TCCD field examinations of M1-MCA in healthy volunteers, with identification rates and image quality comparable to a single-reference examiner. Substantial inter-examiner variability was observed, highlighting the importance of tailored training and competency assessment. Research is required to evaluate TCCD use by HEMS physicians under real-world prehospital conditions.