The Truth about the FAST ExamNick Tadros, MS4June 2007

Objectives

• Components of the FAST exam

• Pitfalls of the exam

• History of the exam from a radiology and EM/Trauma perspective and the Time to Ultrasound Hypothesis

• Recent research

Focused Assessment by Sonography in Trauma (FAST)

Four Primary Views • The right upper quadrant

(RUQ) • The subxiphoid • The left upper quadrant

(LUQ) • Suprapubic • Other views are often

used

• 1/2 of the positive tests will reveal blood in the RUQ

Perihepatic Pericardial

Pelvic Perisplenic

www.Trauma.org

Pitfalls in the FAST Exam

• Failure to scan Morison's pouch in the vertical plane, ideally from the midclavicular line. A horizontal scanning plane in the patient's midaxillary line may miss free fluid.

• Excessive focus on the required views. • Failure to scan systematically and slowly through the

four areas in real time. • Failure to identify clotted blood. • Failure to consider ascites as a cause for free fluid. • The only thing worse than a slow FAST is an

inaccurate FAST.

http://www.cpr.org.tw/ettc/fast_exam.htm

“Positive” FAST Exam

Normal view of Morrison’s Pouch

“Positive” FAST of Morrison’s Pouch

www.medical.philips.com

Pericardial Effusion

Normal subcostal view of pericardium“Positive” FAST demonstrating

pericardial effusion

www.medical.philips.com

Positive FAST in a Patient with Ascites

Liver parenchyma

Perihepatic fluid collection

www.frca.co.uk/ images/A-031.jpg

The FAST Exam in the Literature

Study n sensitivity(%) specificity(%) npv(%)Ballard et al, 1999 102 28 99 85

Boulanger et al, 1996 400 81 97 96

Chiu et al, 1997 772 71 100 98

Coley et al, 2000 107 38 97 78

Hoffmann et al, 1992 291 89 97 93

Ingeman et al, 1996 97 75 96 92

Kern et al, 1997 518 73 98 98

Liu et al, 1993 55 92 95 84

McElveen et al, 1997 82 88 98 96

McKenney et al, 1996 996 88 99 98

Rozycki et al, 1993 470 79 96 95

Rozycki et al, 1995 365 90 100 98

Rozycki et al, 1998 1227 78 100 99

Shackford et al, 1999 234 69 98 92

Thomas et al, 1997 300 81 99 98

Tso et al, 1992 163 69 99 96

Wherret et al, 1996 69 85 90 93

Yeo et al, 1999 38 67 97 93

Total 6324 75 98 94

Courtesy of Mark Brown

The exam is supposedly so good that it even got it’s own scoring system…

Quantification of Fluid on Screening Ultrasonographyfor Blunt Abdominal Trauma

• 2693 patients between April 1994 and Dec 1998• All examinations were performed in the presence of a staff or

resident radiologist and interpreted prospectively by radiologists. Patients’ bladders were distended with 200 to 300 mL of sterile saline via Foley catheter if empty at the start of the examination

• The presence or absence of fluid (free or loculated) in each of the 7 regions examined was recorded. On the basis of a previous study,23 isolated anechoic pockets of fluid in the cul-de-sac in women of reproductive age were considered physiologic and not included.

• A simple scoring system was developed, which quantified the amount of fluid attributable to trauma by counting the number of intraperitoneal and extraperitoneal abdominal recesses in which nonphysiologic fluid was seen on screening ultrasonography

Sirlin et al. Quantification of fluid on screening ultrasonography for blunt abdominal trauma: a simple scoring system to predict severity of injury. Journal of Ultrasound in Medicine. 20(4):359-64, 2001 Apr.

Fluid Score Results

History of the Ultrasound and TraumaAn Emergency Medicine Perspective

• Ultrasound was first described in the detection of free peritoneal fluid by Goldberg et al in 1970

• Sonography in the evaluation of trauma patients was developed by European surgeons more than 10 years later

• Reports of the technique started to appear in the North American literature in 1989

• First prospective study of ultrasound performed by non-radiologists in this country was published in 1992

• Emergency physician use of this modality was reported by Jehle et al. in 1993

• Exam became known by the FAST acronym in 1996

Fluid and Ultrasound

Goldberg et al. in 1970 described the evaluation of ascites by ultrasound, not blood!

Goldberg BB. Goodman GA. Clearfield HR. Evaluation of ascites by ultrasound. Radiology. 96(1):15-22, 1970 Jul.

The Radiologists Prospective

• Blood is a dynamic substance and is NOT anechoic initially!

• When a clot begins to retract after a certain time it leaves behind anechoic plasma

• Very similar to free fluid

• Hematomas contain a variable amount of internal echoes during the first month, and then gradually become anechoic1

1Wicks JD. Silver TM. Bree RL. Gray scale features of hematomas: an ultrasonic spectrum. American Journal of Roentgenology. 131(6):977-80, 1978 Dec

1989 Article from Germany

“Sonographically, recent injuries of the liver show echo-rich, non-homogeneous lesions which may contain smaller echo-free portions. Older lesions become increasingly devoid of echoes and become increasingly demarcated from normal liver parenchyma”

Grabenwoger F. Dock W. Pichler W. Farres MT. Metz V. Diagnosis of liver trauma: ultrasound versus computed tomography [German] Rofo: Fortschritte auf dem Gebiete der Rontgenstrahlen und der Nuklearmedizin. 150(2):163-6, 1989 Feb

First American Journal Article

• Sonography versus peritoneal lavage in blunt abdominal trauma

• Sen 84%• Accuracy 86%• Predictive Value 89%

• “The results demonstrate that sonography cannot replace peritoneal lavage in the diagnosis of blunt abdominal trauma….sonography and peritoneal lavage are not competing, but rather, are complementary examinations”

• NO mention of technique or definition of a “positive” ultrasonic exam

Gruessner R. Mentges B. Duber C. Ruckert K. Rothmund M. Sonography versus peritoneal lavage in blunt abdominal trauma. Journal of Trauma-Injury Infection & Critical Care. 29(2):242-4, 1989 Feb.

First ER Literature Reference

The presence of an anechoic (black) stripe between the liver and the right kidney (Morrison's pouch) was interpreted as a positive study, and the absence of this finding was interpreted as a negative study.

Jehle D. et al. Emergency department ultrasound in the evaluation of blunt abdominal trauma. American Journal of Emergency Medicine. 11(4):342-6, 1993 Jul.

What did the Radiologists have to say?

B-Mode Sonography of 1980

Think of it like your parent’s 8-track player…

Phantom Test Box

Results of B-Mode Scans

• All fluids imaged sonographically were clearly detectable as echo-free regions

• The results indicate that internal echoes within the fluid are not dependent on the nature or concentration of a solute, nor is their presence a result of high viscosity

• “Pathologic fluid collections…may show little acoustic enhancement”

Filly RA. Sommer FG. Minton MJ. Characterization of biological fluids by ultrasound and computed tomography. Radiology. 134(1):167-71, 1980 Jan.

But…

“Blood clots in water showed a decline in echogenicity throughout the experiment. The A-mode imaging was effectively able to follow blood clot echogenicity changes under these controlled conditions”

Peter DJ. Flanagan LD. Cranley JJ. Analysis of blood clot echogenicity. Journal of Clinical Ultrasound. 14(2):111-6, 1986 Feb

Radiology Journals

• Abdomens were scanned for free fluid and for parenchymal heterogeneity in visceral organs; scans that depicted these were considered positive

• In the presence of medical ascites (e.g. cirrhosis or other cause of nontraumatic intraperitoneal fluid), free fluid was considered positive because hemoperitoneum could not be excluded

Farahmand, N, Sirlin, CB, Brown, MA, et al. Hypotensive patients with blunt abdominal trauma: performance of screening US. Radiology 2005; 235:436

Does Time Matter?

• 72 Patients• US performed by PGY-2 – PGY-8 (ER Docs?)• Initial FAST exam 63.5 min after trauma

• 61.2% performed within 60 min

• “If an anechoic or echo-free space was recognized in Morison’s (hepatorenal) pouch or Douglas’ cul-de-sac, we took it as hemoperitoneum”

• Sen 86.7%• Spec 100%• Accuracy 97.2%

Kimura A, Otsuka T: Emergency center ultrasonography in the evaluation of hemoperitoneum: A prospective study. J Trauma 31:20, 1991

Kimura A, Otsuka T: Emergency center ultrasonography in the evaluation of hemoperitoneum: A prospective study. J Trauma 31:20, 1991

Kimura A, Otsuka T: Emergency center ultrasonography in the evaluation of hemoperitoneum: A prospective study. J Trauma 31:20, 1991

Not so FAST…

• The FAST examination was considered positive if it demonstrated evidence of free intra-abdominal fluid

• FAST examination results were compared with CT scan findings, noting the discordance

• FAST examination had a sensitivity of 42%, a specificity of 98%, a positive predictive value of 67%, a negative predictive value of 93%, and an accuracy of 92%

• Six patients with false-negative FAST examinations required laparotomy for intra-abdominal injuries

• Of the 313 true-negative FAST examinations, 19 patients were noted to have intra-abdominal injuries without hemoperitoneum and 11 patients were noted to have retroperitoneal injuries

• Use of FAST examination as a screening tool for blunt abdominal trauma in the hemodynamically stable trauma patient results in underdiagnosis of intra-abdominal injury. Hemodynamically stable patients with suspected BAI should undergo routine CT scanning

Miller, MT, et al. Not so FAST. J Trauma 2003; 54:52

The 2006 SOAP TrialSonography Outcomes Assessment Program

PLUS = point-of-care, limited ultrasonography

SOAP Trial Results

• Time to operative care was 64% less for PLUS compared to control patients.

• PLUS patients – underwent fewer CTs (odds ratio 0.16)– spent 27% fewer days in hospital– had fewer complications (odds ratio 0.16)– charges were 35% less compared to control

Melniker et al. Randomized controlled clinical trial of point-of-care, limited ultrasonography for trauma in the emergency department: the first sonography outcomes assessment program trial.. Annals of Emergency Medicine. 48(3):227-35, 2006 Sep

The Fallacy of the Secondary Examination

• Hypothesis: A repeat abdominal ultrasound may allow for the duration necessary to accumulate the prerequisite amount of blood for detection by the majority of surgical ultrasound operators

• Criteria: Secondary ultrasounds (SUS) performed between 30 until 24 hours after admission

• Technique: All US and SUS exams were considered positive if any intraperitoneal fluid was identified

Blackbourne et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. Journal of Trauma-Injury Infection & Critical Care. 57(5):934-8, 2004 Nov

Blackbourne et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. Journal of Trauma-Injury Infection & Critical Care. 57(5):934-8, 2004 Nov

Blackbourne et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. Journal of Trauma-Injury Infection & Critical Care. 57(5):934-8, 2004 Nov

Common Myth

Rozycki GS, Ochsner MG, Jaffin JH, Champion HR. Prospective evaluation of surgeons’ use of ultrasound in the evaluation of trauma patients. J Trauma. 1993; 34: 516–527

Chief of Surgery at Vermont (where Dr. Gosslin trained!)

Conclusions

• Most Trauma and ER literature incorrectly identifies intraperitoneal blood as anechoic– One hypothesis for this is that the time between

trauma and ultrasound is sufficient enough for the clot to begin to separate

• Secondary exam is more sensitive because the separation of plasma and clot not more bleeding

• Because most exams do correctly identify old clot, the FAST exam is still a useful tool for diagnosing bleeding if a sufficient time has passed since injury