FAST but out of Focus?The focused ultrasound for trauma; assessing accuracy and techniques.

Margaux Snider MS4 September 2007

What is the FAST?• Focused Assessment with Sonography for

Trauma: A bedside ultrasound exam done during trauma to evaluate for intra-abdominal injury

• May include many views (up to 12) but always includes 4 main views:

1. Morrison’s pouch – RUQ, hepato-renal recess

2. Pericardium – subxiphoid, or long-axis parasternal

3. LUQ, Spleno-renal recess4. Pouch of Douglas – suprapubic,

between rectum/uterus and bladder

FAST in the Emergency RoomWhy do a FAST in the first place?

•Represents a quick method to assess for hemorrhage or abdominal injury without interruption of resuscitation (unlike CT)

•Poses low to no risk of further injury to already potentially unstable patient (1-2% risk of bowel perforation with diagnostic peritoneal lavage)

The Literature• Study in 1970 by Goldberg, established ascites as

anechoic by ultrasound1.

• Several studies following this began to characterize various fluids from ascites to clotted blood and hematomas via ultrasound2,4-8.

• North American radiologists began studying US for use in trauma starting in 198911,12

• Emergency medicine physicians began prospective studies using ultrasound to find free fluid in a trauma setting starting in 199313.

Literature Cont.

• Jehle and subsequent studies13-20 cited Goldberg’s identification of ascites as anechoic and inaccurately used blood and “free fluid” (including ascites) as interchangeable.

• Ultrasound in trauma became known as the FAST acronym in 1996, has been added to most level 1 trauma center ATLS algorithms11,15 . However the training is still focused on assessing solely for the presence of an anechoic stripe.

• Several studies have attempted to address the variable sensitivity of the FAST, examining such variables as use of portable US20, retroperitoneal bleeding21-23, and size of anechoic stripe29.

A positive exam in the EM literature is indicated by the presence of an anechoic stripe/region in one of the four main views. Anechoic stripe

A positive exam in the early Radiology literature includes assessing for heterogeneous echogenicity and parenchymal echo abnormalities

Normal

…The Images

The Anechoic StripeAn anechoic stripe on the FAST is thought to be

the definitive sign of a positive exam and represent the presence of hemoperitoneum 14,15

What is actually anechoic on ultrasound?1. Fluid – such as ascites1,5 (not static blood)2,4,7

2. Active flow of blood – as in blood vessels8,9

3. Older hematoma – representing separation of plasma and clot4,6,7

Blood on Ultrasound by Radiologists

Fig. above Ultrasound of phantom containing, from left to right: water (H20), packed red cells (PRC), hemolysate (H), whole blood (WB), serum (S) and water.

Note that both serum and water created the most hypo-echoic regions, whereas whole blood and PRC appear relatively heterogeneous to the surrounding tissue; not anechoic

So what’s the problem?Blood from a newly formed hematoma, as would be

developing in a trauma patient, is not anechoic initially. It appears as a collection of heterogeneous internal echoes, similar to the echogenicity seen in bowel loops and gradually becomes anechoic over time 4,7,10

Although FAST examiners are frequently finding anechoic regions on exam, it more likely represents increased time of bleeding, and subsequent separation of serum out from plasma. However, many additional bleeds and early hematomas are potentially being missed.

Summary of Concerns

• Lack of consistency: Multiple ED studies on the FAST have shown a very wide range of sensitivity and specificity values, from 28%-92%; and 95-100% respectively 11,12,15-21.

• Limited Criteria: Almost all of these studies (those that did specify their criteria) used solely the presence of an anechoic stripe to delineate positivity.

• Faulty Assumptions: 1.These studies routinely cite a study assessing

ascites as evidence for the appearance of blood on ultrasound. They routinely confuse “free fluid,” which could be from a variety of causes, with hemoperitoneum

2.The study documenting increased sensitivity of the FAST with serial exams postulated the newly found anechoic stripe represented increased bleeding over time24 This study, however, failed to specify the time from the actual trauma to the FAST exam, documenting only the time from initial to follow up FAST exam and did not consider changing blood character as a confound rather than increasing amounts of blood.

Hypotheses for proposed study

H1: Poor sensitivity and high false negative values may represent failure to consider increased echogenicity of surrounding organs and poorly visualized organ edges (parenchymal echo abnormalities) as a positive exam.

H2: Presence of anechoic stripe on FAST with repeat exam may represent increased time to exam from trauma, not increased bleeding amount

Study Proposal

Prospective Study Participants:

• Patients arriving at OHSU emergency department for whom the trauma system has been activated.

• Patients whom the trauma team deems appropriate to receive a FAST exam, regardless of documented blunt abdominal trauma.

• Patients enrolled in study must have received per team discretion both a FAST and abdominal CT or abdominal surgery (to allow for verification of blood/fluid presence, or organ injury)

• Patients may be men or women 18-80 years old.

• Reasonable approximation of time of trauma must be attainable

Study Proposal

Methods – Part 1

4 view frames (RUQ, pericardium, LUQ, suprapubic) of participant FAST (ideally a video recording of entire FAST exam), saved, identifying data removed.

Approximate time of trauma and time of FAST recorded at arrival

Exam is assessed by ED physician or resident certified for FAST exam at time of trauma.

Classified as: • Positive – based on presence of anechoic stripe

or anechoic fluid collection in any 1 or more of 4 views

• Negative – based on absence of anechoic region in all 4 views

Study Proposal

Methods – Part 24 views which have been saved are then

reinterpreted by blinded sonographers or ultrasound trained radiologists (unaware of final presence of fluid or ED read of FAST)

They are asked to classify the exam as follows:Positive 1: presence of anechoic stripe/collection

in any 1 or more of 4 viewsPositive 2: absence of anechoic stripe/collection

but presence of increased heterogeneous echogenicity or poorly visualized organs (parenchymal echo abnormalities)

Negative: absence of either 1 or 2

Study Proposal

Confirmation of FindingsAll subjects are documented as +/- free

intra-peritoneal fluid or blood based on CT or abdominal surgery findings.

**Would be ideal to be able to quantify fluid – but not sure how to do this radiographically**

• Intra-parenchymal injury observed on CT scan or during surgery without peritoneal fluid/blood will be excluded as solid organ injury is not specifically being assessed other than edge/echo abnormalities as it contributes to

identifying peritoneal fluid collections on ultrasound.• Any fluid visible on CT scan as read by radiologist, or

>50ml fluid visualized during surgery will be considered +.

Study Flow ChartInitial FAST obtained

ED Physician assessment – real time

Positive

Negative

Sonographer assessment

Positive – group 1

Positive – group 2

NegativeConfirmation of fluid presence

CT Scan Abdominal Surgery

+/-

Time from trauma to FAST obtained

Quantification of fluid?

Outcomes• Accuracy, Sensitivity, Specificity, of ED

readers and blinded sonographers

• Inter-rater reliability among ED and sonography assessors

• NPV and PPV of FAST for both groups

• Concordance of categorization: Are the same exams being categorized correctly or incorrectly among both ED physicians and sonographers

Outcomes cont.• Assess how sonographer positive 2’s are

recorded by ED physicians – are they always recorded as negative, or are they deemed positive? Or indeterminate?

• Assess time to FAST to determine: 1)whether longer time = more positive FAST

exams among both groups 2) whether longer time = significantly more

anechoic positives

• If possible, could examine the relationship of time to FAST exam and quantity(?) of actual fluid observed, comparison with presence/absence of anechoic stripe

Thank You

References1. Goldberg BB, Goodman GA, Clearfield HR. Evaluation of Ascities by Ultrasound.

Radiol. 96: 15-22; 1970.2. Kaplan GN, Sanders RC, et al. B-Scan Ultrasound in the management of patients

with occult abdominal hematomas. J Ultrasound. 1 (1): 1-15; 1973. 3. Goldberg BB. Ultrasonic Evaluation of Intraperitoneal Fluid. JAMA. 235(22):2427-

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and comuted tomography. Radiol. 134:167-171; 1980.7. Siegel B, Coelho JC, et al. Ultrasonography of blood during stasis and coagulation.

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Radiol. 145:139-141; 1982.9. Dinkel E, Lehnart R, et al. Sonographic evidence of intraperitoneal fluid: an

experimental study and its clinical implications. Pediatr Radiol. 14: 299-303; 1984. 10. Peter DJ, Flanagan LD, Cranley JJ. Analysis of blood clot echogenicity. J Clin

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hemoperitoneum: a prospective study. J Trauma. 31(1):20-3; 1991. 12. Tso P, Rodriguez A, et al. Sonography in blunt abdominal trauma: a preliminary

progress report. J Trauma. 33(1):39-44; 1992.13. Jehle D. et al. Emergency department ultrasound in the evaluation of blunt

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References cont.15. Rozycki GS, Ochsner MG, et al. Early detection of hemoperitoneum by

ultrasound examination of the right upper quadrant: a multicenter study. J Trauma. 45(5):878-883; 1998.

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17. McKenney K. Ultrasound of blunt abdominal trauma. Radiol Clin North Amer. 37(5): 879-893; 1999.

18. Shanmeganathan K, Mirvis SE, et al. Hemoperitoneum as the sole indicator of abdominal visceral injuries: a potential limitation of screening abdominal ultrasound for trauma. Radiol. 212:423-430; 1999.

19. Lingawi SS, Buckley AR. Focused abdominal ultrasound in patients with trauma. Radiol. 217:426-429; 2000.

20. Blaivas M, Theodoro D. Intraperitoneal blood missed on a FAST examination using portable ultrasound. Am J Emerg Med. 20:105-107; 2002.

21. Miller MT, Pasquale MD, et al. Not so Fast. J Trauma. 54:52-60; 2003.22. Sirlin CB, Brown MA, et al. Screening US for blunt abdominal trauma: objective

predictors of false negative findings and missed injuries. Radiol. 229:776-774; 2003.

23. Poletti PA, Kinkel K, et al. Blunt abdominal trauma: should US be used to detect both free fluid and organ injuries? Radiol. 227:95-103; 2003.

24. Blackbourne LH, Soffer D, et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. J Trauma. 57:934-8; 2004.

25. Sato M, Yoshii H. Reevaluation of ultrasonography for solid-organ injury in blunt abdominal trauma. J Ultrasound Med 23:1583-1596; 2004.

26. Farahmand N, Sirlin CB, et al. Hypotensive patients with blunt abdominal trauma: performance of screening US. Radiol. 235:436-443; 2005.

27. Nural MS, Yardan T, et al. Diagnostic value of ultrasonography in the evaluation of blunt abdominal trauma. Diagn Interv Radiol. 11:41-4; 2005.

References cont.

28. Melniker LA, Leibner E, 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. Ann Emerg Med. 48(3):227-235; 2006.

29. Ma OJ, Gaddis G. Anechoic stripe size influences accuracy of FAST examination interpretation. Acad Emerg Med. 13:248-253;2006.

30. Friese RS, Malekzadeh S, et al. Abdominal ultrasound is an unreliable modality for the detection of hemoperitoneum in patients with pelvic fracture. J Trauma. 63(1):97-102; 2007.