Page 53 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars
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                 is negative it is recommended to repeat the examination every 15 minutes.2,77 Repeated ab- dominal US scans may lead to a 50% reduction of false negatives.79 However, a hemorrhage in the retroperitoneum or any solid organ injuries cannot be detected reliably with FAST. So, a negative FAST does not compensate a high suspicion of abdominal hemorrhage.
A (non) traumatic pneumoperitoneum is almost invariably caused by gastrointestinal per- foration. When detected prehospitally this might steer early treatment and transportation. Sensitivity and specificity of abdominal US for pneumoperitoneum is 85–90% and 100%. In experienced hands it can be as good as CT; an amount as small as 1 ml of free air can be de- tected.80–82 Thus, it appears plausible to use PHUS also for this indication.
In their meta-analysis, Stengel et al. concluded that US for blunt abdominal trauma does not decrease the laparotomy rate or mortality. Nevertheless, the number of ordered CT scans de- creased by 50%. However, this might reflect a false sense of security due to the low sensitivity of abdominal ultrasound for both free fluid and organ lacerations.7 Montoya also reported that US led to fewer CT scans. In addition, however, they found a decreased time to appro- priate interventions, shortened hospital stay, and decreased use of healthcare resources.78
Figure 2.8 Hemoperitoneum at the hepatorenal recess
An ultrasound image of the hepatorenal recess (Morison’s pouch). A phased-array cardiac transducer was used with the abdominal settings. The left arrow indicates the diaphragm. The right arrow indicates the hepatorenal recess with a hypoechoic collection between the liver (L) and the right kidney (K). This is the image of free intra- peritoneal fluid and is very suggestive for intraperitoneal hemorrhage when encountered in a trauma victim.
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