Page 140 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 6
of a pneumothorax, sound waves reflect off of the parietal and visceral pleura. These two lay- ers can be observed moving in relation to each other. These so-called comet-tail artifacts and lung sliding sign demonstrate that the two pleural layers lie together, and this helps to exclude the existence of a pneumothorax.12,13
The PREP method is specifically designed to be used out of hospital or in the Emergency De- partment (ED). Five US windows are defined and have to be sequentially scanned looking for abnormal artifacts, fluid-air interfaces, and air or fluid collections in the chest and abdomen. The five windows in order of examination are: right lung, liver, and right kidney; left lung, spleen, and left kidney; uterus, bladder, and recto-uterine pouch; heart and pericardium; and abdominal aorta. Just like the eFAST, a PREP examination has to be completed within three minutes.
We use a portable US machine weighing 3.5 kg (MicroMaxx, Fujifilm SonoSite Inc., Bothell, WA, USA) equipped with a 5–1 MHz broadband phased-array transducer.
For every scramble (we prefer this military-derived term to indicate the typical swift dis- patch of the HEMS), a large amount of data are collected by the HEMS physicians in a custom-made database.
Data were selected from the database of all scrambles between January 1, 2007 and June 1, 2010 in which one or more US examinations of the chest and its contents were performed. The following data were selected: patient characteristics (gender, age, and estimated weight), US examination characteristics (performing physician, its timing [on arrival at the patient, during treatment, before departure, during transport, or on arrival at the hospital], dura- tion, quality of imaging [good, moderate, or poor], specific location [thorax, pericardium, or heart], findings per location), and diagnosis based on US examination. Also, the impact of the US examination on treatment decisions was recorded.
The results of chest X-ray study (CXR) and computed tomography (CT) examinations of the patients who were transported to our hospital were recorded to calculate sensitivity, spec- ificity, positive predictive value (PPV), and negative predictive value (NPV) of prehospital portable US for the diagnosis of pneumothorax. CT scan results were used as a reference.
Comparison of quality of imaging and body weight was done only in patients aged 18 years and older because their body weight correlates better with body mass index (BMI) than in younger patients.14
Data were collected in an Excel spreadsheet (Microsoft Corp., Redmond, WA, USA) and