Page 145 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars
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                 Prehospital chest ultrasound by a Dutch helicopter emergency medical service 143
Discussion
US is used increasingly in the prehospital setting, and its value in this context seems promis- ing. There is increasing emphasis on US training of physicians working in Emergency Med- icine.6–9 With an increasing number of trained physicians using US in the field, its added value may become clearer. The value of US on its own already has been established.
Blaivas showed in 176 patients that non-portable US for pneumothorax has a good sensitivity and specificity (98.1% and 99.2%, respectively) and similar PPV and NPV.15 Nagarsheth and Kurek showed comparable results.16 US can therefore be said to reliably detect and exclude the presence of pneumothorax. In our study, the sensitivity and NPV are not so high due to a large number of false negatives.
An explanation could be that we use US in the prehospital setting where it is more difficult to interpret the US images due to difficult access to the chest, time pressure, low ambient light, and other distractions. Furthermore, the HEMS physicians have different levels of experience and the screen is smaller and of inferior quality compared to non-portable US machines.
Another factor that may contribute to the low sensitivity and NPV found in this study is the fact that we recorded CT scans that showed a minimal anterior pneumothorax as a pos- itive test result. This may be the cause of the large number of false-negative examinations in corresponding US and CXR examinations. Furthermore, a pneumothorax can develop in a short period of time, even after it has been properly ruled out by US. This is especially true in patients who are intubated and ventilated with positive airway pressure.
Our results show a high incidence of US use in children under the age of four years. Gerritse showed that our HEMS scrambles relatively often for young children and that these flights are cancelled less often than flights for adult victims.17 Reasons for dispatching the HEMS for children that Gerritse found included hypovolemic shock caused by diarrhea or reduced intake, child abuse, sudden infant death syndrome, asphyxia at birth, and trauma around the home. There is a low threshold for HEMS physicians to perform an US examination during resuscitation of children. The US can provide sufficient information to decide to stop CPR, and additionally, it provides images to allow for a clear explanation to parents or bystanders why CPR was stopped.
The quality of imaging is reduced by an increase in body weight in adults. Due to the design of our database, there was no BMI available, and we cannot determine if the recorded imag-
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