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FAST Underperforms in Patients with Hemodynamic Instability

FAST when performed by radiology residents had low sensitivity for detecting hemoperitoneum in hemodynamically unstable trauma patients.

Advantages of the Focused Assessment with Sonography for Trauma (FAST) include bedside performance, lack of ionizing radiation, ability to perform serial examinations, and 70% to 90% sensitivity overall for detecting hemoperitoneum. However, the sensitivity of FAST in blunt trauma patients with pelvic fracture seems to be lower (JW Emerg Med Feb 9 2007) and its accuracy in patients with potential hemodynamic instability is uncertain (JW Emerg Med Sep 25 2009). In a prospective observational study, researchers at a major trauma center in Norway assessed the accuracy of FAST for detecting hemoperitoneum in 204 patients who presented with potential hemodynamic instability (systolic blood pressure 90 mm Hg, pulse rate 120, or base deficit 8) during 2005–2006. Standard 4-view FAST was performed at the bedside by radiologists (mostly residents; mean years of training, 3.4) who had undergone at least 6 weeks of training in abdominal ultrasound examinations.

FAST results were compared with findings of computed tomography (CT), diagnostic peritoneal lavage, exploratory laparotomy, or observation. Overall, FAST results yielded 75 true negatives, 10 false negatives, 16 true positives, and 3 false positives. Sensitivity and specificity of FAST for the detection of hemoperitoneum were 62% and 96%, respectively; positive and negative predictive values were 84% and 89%, respectively; and overall accuracy was 88%.

Comment: False-negative FAST results have been ascribed to pelvic fracture, spinal injury, subcutaneous emphysema, obesity, and a lag in time between performance of FAST and CT. However, in patients with signs of hemodynamic instability, the lag time is less likely to play a role. This study's findings add to the evidence that a negative FAST result in patients with signs of hemorrhagic shock owing to intraperitoneal trauma should lead to diagnostic peritoneal lavage — the critical aspect being the initial peritoneal aspirate — or to CT, if CT can be performed rapidly and safely in the confines of the trauma bay.

— John A. Marx, MD, FAAEM

Published in Journal Watch Emergency Medicine October 2, 2009

Citation(s):

Gaarder C et al. Ultrasound performed by radiologists — Confirming the truth about FAST in trauma. J Trauma 2009 Aug; 67:323.

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