Focused trauma sonography misses some abdominal injuries

CHICAGO - Focused abdominal sonography for trauma (FAST) may miss many cases of abdominal injury in blunt trauma patients, according to findings from two studies presented Monday at the RSNA meeting. The results suggest that a negative FAST exam should not be relied upon to rule out abdominal injury.

The results of the first study were presented by Pierre Polletti, M.D., of the University of Maryland. FAST was performed in 531 clinically stable trauma patients by the surgical team upon arrival in the emergency room. The FAST exams were rated as positive, negative or indeterminate for free peritoneal fluid. An abdominal CT then was performed on all patients to detect intraabdominal organ injury, and the FAST and CT findings were compared.

CT revealed that 13% (71/531) of the patients had organ injury either with or without free peritoneal fluid. For detection of free fluid, FAST had low sensitivity (36%), high specificity (97%), and moderate overall accuracy (88%). The results were similar for detection of organ injury: sensitivity 29%, specificity 97%, accuracy 85%.

Twenty-two patients had life-threatening injuries that required either surgery or angiographic embolization. Of these, FAST was falsely negative in 8 (36%), while CT was falsely negative in one patient.

The second study was presented by C. W. Hanemann, M.D., of New Orleans, LA. The researchers identified 581 patients who had undergone FAST from January 1, 1996 to March 30, 1999 at their Level I trauma center. Of these, 29 patients were excluded due to insufficient follow-up data, leaving a sample of 552 patients. Most patients had sustained blunt trauma.

All ultrasound studies were performed using a portable unit in the trauma section of the ER by a radiologist or radiology resident within 30 minutes of patient arrival. FAST results were recorded as positive or negative for pericardial fluid or free fluid within the peritoneal or pleural spaces. No indeterminate exams were included in the analysis. FAST findings were compared to findings on abdominal CT, diagnostic peritoneal lavage, surgery, or patient observation.

For detection of abdominal injury, FAST had a sensitivity of 80%, specificity of 96%, and accuracy of 95%. Of the 41 patients with abdominal injuries, 8 (20%) were missed using FAST; all were correctly identified by CT. Most of these false negative exams had little or no hemoperitoneum.

Dr. Hanemann concluded that FAST is unreliable for detection of abdominal injuries with no significant hemoperitoneum.

By Deborah Barnes contributing writer
November 30, 1999

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