Transcript FAST but out of Focus?

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 recess
4. Pouch of Douglas – suprapubic, between
rectum/uterus and bladder
FAST in the Emergency Room
Why 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 (12% 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.
…The Images
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 Anechoic Stripe
An 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
 Note that both serum and
water created the most hypoechoic regions, whereas
whole blood and PRC appear
relatively heterogeneous to
the surrounding tissue; not
anechoic
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.
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 11,12,1521.
•
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 2
4 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 views
Positive 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 Findings
All subjects are documented as +/- free intraperitoneal 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 Chart
Initial FAST
obtained
ED Physician
assessment –
real time
Sonographer
assessment
Positive
Time from trauma
to FAST obtained
Negative
Positive – group 1
Positive – group 2
Confirmation of
fluid presence
CT Scan
Negative
Abdominal Surgery
+/-
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
References
1. 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):2427-2430;
1976.
4. Wicks JD, Silver TM, Bree RL. Gray Scale Features of Hematomas: An ultrasonic spectrum.
Am J Roentgenol. 131:977-980; 1978.
5. Edell SL, Gefter WB. Ultrasonic differentiation of types of ascitic fluis. AJR. 133:111-114;
1979.
6. Filly RA, Sommer G, Minton J. Characterization of biological fluids by ultrasound and
comuted tomography. Radiol. 134:167-171; 1980.
7. Siegel B, Coelho JC, et al. Ultrasonography of blood during stasis and coagulation. Invest
Radiol. 16:71-6; 1981.
8. Jeffrey RB, Laing FC. Echogenic clot: a useful sign of pelvic hemoperitoneum. 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 Ultrasound.
14:111-116;1986.
11. Kimura A, Otsuka T. Emergency center ultrasonography in the evaluation of
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 abdominal
trauma. American Journal of Emergency Medicine. 11(4):342-6, 1993 Jul
14. Boulanger BR, Brenneman FD, et al. The indeterminate abdominal sonogram in
multisystem blunt trauma. J Trauma. 45(1):52-56; 1998.
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.
16. Salen PN, Melanson SW. The focused abdominal sonography for trauma (FAST)
examination: considerations and recommendations for training physicians in the use of a
new clinical tool. Acad Emerg Med. 7:162-168; 1999.
17. McKenney K. Ultrasound of blunt abdominal trauma. Radiol Clin North Amer. 37(5): 879893; 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.