Page 162 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 7
Discussion
In 12.6% of the patients an abdominal PHUS examination impacts treatment. This suggests that PHUS might change treatment decisions in patients suspected of abdominal injuries. In our opinion, this reaffirms the use of ultrasound even with a low likelihood of abdominal injury. In our HEMS, abdominal PHUS is most often performed after RTAs and falls from heights, both associated with blunt abdominal trauma. We found a high specificity and ac- curacy for free abdominal fluid, but low sensitivity. The implication of the low sensitivity of PHUS (31.3%) might be that, despite a negative PHUS, health care providers should be vigilant for any previously undetected intraperitoneal hemorrhage.
The present study confirms previous research that concludes PHUS alters or at least supports treatment but found a lower proportion of affected patient care.10,12 In a prospective study, Walcher demonstrated that PHUS changed patient treatment in 30%, and choice of desti- nation hospital in 22%.10 They specifically included patients suspected of blunt abdominal trauma. This might indicate that PHUS has more impact when the a priori chance of ab- dominal hemorrhage is high. O’Dochartaigh found a higher amount in chest and abdominal US (23–57% depending on the mission type and medical crew composition, 32% overall).12 In this retrospective analysis, they looked for supported treatment instead of specific alter- ations. Similar to our previous study, it appears that treatment decisions are influenced more frequently in patients with chest injuries, probably because of the availability of effective treatment options such as thoracostomy and chest drain placement.11 We chose a retrospec- tive study design with a database not designed for the study. HEMS physicians fill out the database after a scramble, therefore recall bias might occur and record keeping may be less accurate. Our study population differs; every patient who underwent abdominal ultrasound was included.
The diagnostic performance we found confirms the results of Blackbourne’s study in an emer- gency room setting.2 We found a sensitivity and specificity of respectively 31.3% and 96.7% that correspond to their respective values of 31.1% and 99.8%. Sensitivity is low and possibly due to factors such as the prehospital setting with its numerous detrimental environmental factors, high stress, time pressure, and relatively short time intervals between the incident and PHUS and the far larger interval after which in-hospital diagnostics are performed. The restricted sonographic view of the pelvis and Douglas’ pouch due to pelvic stabiliza- tion devices provides another possible explanation. Importantly, abdominal hemorrhage is a dynamic process; time is required for its volume to increase and become detectable by ul- trasound.17 Blackbourne found that the sensitivity increased from 31.1% to 72.1% after a mean interval of 250.1 minutes between US examinations. We could not confirm this because, in