As a third year medical student at a busy trauma center, one of my jobs was to hold a bag of saline connected to the trauma victim’s abdomen and throw the bag to the ground when it emptied. While I helped with diagnostic peritoneal lavages, radiology residents bumped their way to the bedside with a probe connected to an unwieldy ultrasound machine. Our trauma surgeons observed with skepticism the radiologists tried to convince us that they could diagnose hemoperitoneum with sound waves.
Since this time, the Focused Assessment with Sonography in Trauma (FAST) has become an important adjunct to the initial evaluation of trauma patients. It allows providers to quickly detect the presence of intraabdominal free fluid, pericardial fluid and now even the presence of a pneumothorax (Extended FAST or E-FAST). Ultrasound training has become routine in emergency medicine and the equipment has become more portable without sacrificing image quality. The American College of Surgeons, Committee on Trauma now endorses FAST in its Advanced Trauma Life Support program.
Despite this progress, the FAST exam has come under recent scrutiny. A study by Fox, et al. looking at pediatric blunt trauma found that while FAST had a 96% specificity[e1] , the sensitivity was poor at 52%.1 Friese, et al. found FAST to have low sensitivity (26%) in blunt pelvic trauma,2 and Gaarder, et al. found the FAST exam underperformed in patients with hemodynamic instability (62% sensitivity).3 Based on these and other studies showing poor sensitivity in specific clinical scenarios, some editorialists are calling for the elimination of sonography in the initial assessment of trauma patients.
To determine the utility of FAST, however, requires a careful look at the data. In none of the three studies was the training of the ultrasonographers reported. Accuracy of FAST exam is highly operator dependent. Also, in the study by Friese, the interval from FAST to laparotomy was over two hours. Considering that most pelvic bleeding is venous it would be interesting to know what the sensitivity would have been immediately prior to surgery.
Advantages to FAST include ability of the treating physician to perform the exam quickly at the bedside, avoidance of an invasive procedure and ionizing radiation, ability to perform serial exams, and has a 70-90% overall sensitivity with >95% specificity for detecting hemoperitoneum.4 In a retrospective validation study at my institution, 696 FAST examinations were documented over a two year period. Exams were performed by attending emergency physicians, all of whom had received one hour of didactic training and one hour of hands on scanning using live models. There were 658 true negative FAST Exams (95%), 6 true positive exams (1%), 38 false negative exams (5%) and 0 false positive exams. Of the 38 (5%) false negative exams, 20 were due to extraperitoneal injuries and only 6 patients with a false negative exam required laparatomy.5
Focused Assessment with Sonography in Trauma remains a useful adjunct to the initial evaluation of the traumatized patient. A positive FAST exam in a hemodynamically unstable patient requires laparotomy and has been shown to decrease time to the operating room.6 Hemodynamically stable patients may undergo careful confirmatory evaluation with diversion to the OR for the development of hypotension. For patients with a negative FAST examination, those with low suspicion of intraabdominal injury may undergo observation with serial examinations, while those with high suspicion of intraabdominal injury require further diagnostic testing.
5. Holmes, et al. FAST ENOUGH? A validation study for focused assessment with sonography for trauma ultrasounds in a Level II trauma center. Am Surg. 2012 Oct;78(10):1038-40.