Feasibility of bedside thoracic ultrasound in the helicopter emergency medical services setting.

INTRODUCTION: Bedside thoracic ultrasound has been shown to be a valuable diagnostic tool in the emergency department. The purpose of this study was to evaluate the feasibility of bedside thoracic ultrasound in the prehospital HEMS setting. SETTING: Air ambulance helicopters during patient transportation. METHODS: This was a prospective pilot study. 71 consecutive, nonpregnant patients over 18 years old were enrolled. While in flight, providers completed limited bedside thoracic ultrasounds with the patient supine and recorded their interpretation of the presence or absence of the ultrasonographic sliding lung sign on a closed data-set instrument. RESULTS: 41 (58%) of the eligible patients had a recorded thoracic ultrasound acquired in flight. The level of agreement in image interpretation between the flight crew and expert reviewer was substantial (Kappa 0.67, CI 0.44-0.90). The reviewer rated 54% of all images as "good" in quality. The most common reason cited for not completing the ultrasound was lack of enough provider time or space limitations within the aircraft cabin. CONCLUSION: The results of this study suggest that, with limited training, bedside thoracic ultrasound image acquisition and interpretation for the sliding lung sign in the HEMS setting is feasible.

Effect of position and weight force on inferior vena cava diameter--implications for arrest-related death.

INTRODUCTION: The physiology of many sudden, unexpected arrest-related deaths (ARDs) proximate to restraint has not been elucidated. A sudden decrease in central venous return during restraint procedures could be physiologically detrimental. The impact of body position and applied weight force on central venous return has not been previously studied. In this study, we use ultrasound to measure the size of the inferior vena cava (IVC) as a surrogate of central venous return in the standing position, prone position, and with weight force applied to the thorax in the prone position. METHODS: This was a prospective, observational study of volunteer human subjects. The IVC was visualized from the abdomen in both the longitudinal and transverse section in the standing and prone positions without weight force applied, and with 100 lbs (45 kg) and 147 lbs (67 kg) of weight force on the upper back in the prone position. Maximum and minimum measurements were determined in each section to account for possible respiratory variation of the IVC. RESULTS: The IVC significantly decreased in size with each successive change: from standing to prone, from prone to prone with 100 lbs (45 kg) weight compression, from prone with 100 lbs (45 kg) weight compression to prone with 147 lbs (67 kg) weight compression (p < 0.0001). The vital sign measurements had no statistical change. CONCLUSIONS: The physiology involved in many sudden, unexpected ARDs has not been elucidated. However, in our study, we found a significant decrease in IVC diameter with weight force compression to the upper thorax when the subject was in the prone position. This may have implications for the tactics of restraint to aid in the prevention of sudden, unexpected ARD cases.