FAST.html
FAST as a predictor of clinical outcome in
blunt abdominal trauma
Benjamin M Terry, MD, MPH
David Blehar, MD
Romolo Gaspari, MD
Department of Emergency Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA
Arthur Maydell, MB ChB, Dip PEC (SA)
Fourie Bezuidenhout, MB ChB
Department of Radiology, Tygerberg Hospital, University of Stellenbosch
Savvas Andronikou, MB BCh, FCRad, FRCR (Lond), PhD
Department of Radiology, University of the Witwatersrand
Corresponding author: A Maydell (atmaydell@hotmail.com)
Abstract
Background.
Peer-reviewed literature demonstrates increasing support for the use of
focused abdominal sonography in trauma (FAST) in the setting of blunt
trauma, one study demonstrating the sensitivity and specificity of FAST
for the detection of free fluid to be 0.64 - 0.98 and 0.86 - 1.00,
respectively, compared with abdominal CT. Utilising ultrasound in
trauma triage increases efficiency and cost-effectiveness and reduces
reliance on CT, compared with using CT alone. There is little evidence
to support relying solely on a negative FAST and physical examination
for patient management.
Method.
A retrospective descriptive study of 172 adult patients who received
FAST for the evaluation of blunt abdominal trauma between 22 July 2007
and 21 January 2008 at Tygerberg Hospital was performed. Ultrasound
findings were correlated with CT scan findings, operative findings if
managed surgically, clinical outcomes whether managed surgically or
conservatively, as well as postmortem findings in deceased patients.
Results.
FAST was negative in 147 (85.5%) patients. Twenty-four (16.3%) of these
patients died from all-cause mortality, none of which was due to
intra-abdominal injury.
Seven patients with negative FAST underwent CT scan
owing to change in clinical course, and 3 patients with negative FAST
underwent laparotomy owing to change in clinical course, with positive
findings in 2 patients – a bowel injury requiring resection (not
seen on CT) and a diaphragmatic rupture seen on CXR. A negative FAST
was shown to be an excellent predictor for the absence of significant
intra-abdominal trauma.
The mortality rate among 25 FAST positive patients was 24% (N=6). Only one of these patients (with a splenic rupture) was suspected to have died from abdominal pathology.
Introduction
Peer-reviewed literature demonstrates an
increasing trend of support for focused abdominal sonography for trauma
(FAST) in the setting of blunt trauma. It is used as the initial
screening tool to detect the presence of intra-abdominal free fluid and
to indirectly confirm abdominal injury as the source of haemorrhage in
haemodynamically unstable patients who would then require emergency
laparotomy before further time is spent on imaging. Previous studies
have demonstrated the sensitivity and specificity of FAST for the
detection of free fluid to be 0.64 - 0.98 and 0.86 - 1.00,
respectively, compared with abdominal computed tomography (CT).1 Some authors in fact argue that FAST is more sensitive than CT for free fluid.2
Randomised controlled trials now show that triage pathways
incorporating ultrasonography result in increased efficiency,
cost-effective evaluation and reduced reliance on CT, compared with
pathways that exclusively utilise CT.3
However, there is much less evidence to support sole reliance on a
negative FAST scan and physical examination for patient management.7
,
8
Haemodynamically stable, negative FAST
patients routinely receive CT scans out of literature-based concern
that ultrasonography may miss solid organ injury. The sensitivity of
ultrasonography for solid organ injury ranges from 0.4 - 0.8, even
after the administration of intravenous contrast agent.9
Despite evidence that the missed solid organ injuries are not
clinically significant, or would be detected during observation without
incurred morbidity, much of the trauma community maintains the
necessity of routine whole-body CT imaging, even without obvious signs
of injury.10
Attributable factors include over-investigation by clinicians motivated
by a fear of litigation, institutional financial gain from CT scanning,
and patient demand for advanced imaging to rule out injury.
Routine whole-body CT imaging is costly and
exposes millions of patients to ionising radiation that could have
immediate and long-term consequences, including the development of
fatal cancers. CT has become central to the evaluation of trauma, with
improvements in speed and resolution leading to lower thresholds for
the use of CT.11
,
12 According
to the report by the National Council on Radiation Protection and
Measurements (NCRP) on population exposure, Americans were exposed to
more than seven times as much ionising radiation from medical
procedures in 2006 as was the case in the early 1980s, with CT and
nuclear medicine studies being the most significant contributors, with
the effective radiation dose from all sources per individual in the USA
population nearly doubling from 3.6 to 6.2 millisievert (mSv) over this
period.13
Longstanding controversy exists about the level of carcinogenic risk attributable to low-level ionising radiation.14
The seventh Biologic Effects of Ionizing Radiation report (BEIR VII)
predicts that, for a standardised US population, an average lifetime
attributable risk exists of one radiation-induced cancer per 1 000
patients receiving a 10mSv effective dose (average abdominal CT), with
approximately half of these cancers expected to be fatal.15 The number of CT scans performed in the US increased from 3.6 million in 1980 to 67 million in 2006.
Studies have demonstrated a significant
cancer risk to the pelvic and abdominal organs as a result of trauma
whole-body imaging, although the risk-benefit is yet unclear. In
addition, CT is a much more expensive investment than ultrasound
– a notable factor in countries with limited resources. It is
important, both from a clinical and cost-effectiveness perspective, to
not only establish the utility of ultrasound, but also to demonstrate
when CT incurs risk and expense without compensatory benefit in patient
outcomes.
This is a preliminary investigation of a
triage pathway that relies on the FAST exam to rule out the need for
further imaging or intervention. It establishes, in a retrospective
manner, that this triage pathway accurately predicts good clinical
outcome without CT.
Methods
A retrospective study was done of 172
patients receiving FAST for blunt abdominal trauma at Tygerberg
Hospital, the academic tertiary referral centre of Stellenbosch
University. Tygerberg Hospital is the second-largest hospital in South
Africa, with 22 500 trauma cases per year. The Trauma (Emergency)
Department is staffed by full-time medical officers, with urgent
referrals available 24 hours a day to in-house radiology residents for
ultrasonagraphy and CT, and a general surgery trauma service for
operative intervention. Patients requiring urgent CT are prioritised
and scanned promptly.
Emergency medicine is a nascent specialty in
South Africa, with formal recognition in 2003 and the first residency
programme established in 2004. Residents in emergency medicine rotate
among various services at the Universities of Cape Town and
Stellenbosch, but were not an integral part of the current study.
All patients from the Trauma (Emergency)
Department between 22 July 2007 and 21 January 2008 who received a FAST
scan as part of the triage protocol were retrospectively enrolled in
the study by utilising the ultrasound request forms submitted by Trauma
Department personnel. Patients sustaining blunt abdominal trauma are
evaluated using a diagnostic tree (Fig. 1), designed to triage the use
of CT to those who would obtain the most clinical benefit, based on
peer-reviewed literature.1
Patients with blunt abdominal trauma, stable vital signs and no obvious
injury underwent serial FAST and physical examinations for 24 hours
without undergoing CT. Patients with positive FAST scans received a
contrasted CT of the abdomen as long as they remained haemodynamically
stable,to identify injuries which would require surgical management. At
any point in the triage pathway, unstable patients underwent immediate
exploratory laparotomy.
Inclusion criteria included patients who
were 18 years and older who suffered blunt abdominal trauma and
received a FAST scan within 24 hours of presentation. Charts were
reviewed for operative findings, CT findings and patient outcome,
including postmortem data. Patients were excluded if chart review,
including patient outcome, could not be completed. Institutional
approval was obtained from Stellenbosch University’s Committee
for Human Research.
The primary outcome in this investigation was
safe discharge or transfer without mortality or morbidity attributable
to abdominal pathology. Secondary outcomes included need for
laparotomy, surgical findings and CT findings.
Patients enrolled by ultrasound request forms
were recorded by medical record number into a Microsoft Excel
spreadsheet that was matched to locate patient charts and record
outcome data. These results were then provided to the primary author,
who analysed the outcome information and categorised patients’
morbidity and mortality according to aetiology.
Results
A total of 172 patients met inclusion
criteria during the selection period. The predominant population
involved was young males, with 131 (76%) male and 41 (24%) female
patients. There were 118 (68.6%) patients between the ages of 20 and
39. Racial characteristics and socio-economic status were not recorded.
Results are presented in Fig. 2. The FAST
exam was negative in 147 (85.5%) patients. Twenty-four (16.3%) of these
patients died from all-cause mortality. The cause of death was
neurological in 18 patients (intracranial injury), infectious in 4
patients (hospital-acquired pneumonia etc.), orthopaedic in 1 patient
(pelvic fractures) and unclear in 1 patient, who underwent a postmortem
examination that showed no abdominal organ injury or free fluid within
the abdomen. Seven patients (4.8%) with negative FAST received a CT
scan owing to change in clinical course. Two of these patients had CT
findings, namely a splenic contusion and a kidney laceration, neither
requiring surgical repair. Three patients with negative FAST underwent
laparotomy owing to a change in clinical course with positive findings
in 2 patients, i.e. a bowel injury requiring resection that was not
detected on CT, and a diaphragmatic rupture seen on chest X-ray with no
other operative abdominal findings.
The mortality rate among 25 FAST positive patients was 24% (N=6),
only slightly higher than the FAST-negative patients. Fig. 3a shows a
FAST-positive ultrasound, with Fig. 3b as a comparison of a
FAST-negative ultrasound. One of the FAST-positive patients sustaining
a splenic rupture was suspected to have died from abdominal trauma.
Three patients died due to neurological injury – one from
multi-organ failure, and one from respiratory failure. Eleven patients
(44%) underwent laparotomy, which showed free fluid with or without
major organ trauma in 91%, and a negative laparotomy in one patient
where CT had indicated a bowel injury. Ten patients (40%) received a CT
scan which reported free fluid in 80% with or without the presence of
major organ trauma. Ten patients (40%) receiving CT underwent
laparotomy with one negative laparotomy performed for a CT report of
bowel injury.
Discussion
Our study demonstrates that the algorithm for
managing blunt abdominal trauma according to current evidence (as shown
in Fig. 1) at Tygerberg Hospital is safe and effective, with the
appropriate use of CT as indicated by FAST and clinical parameters. CT
of the abdomen was not performed routinely for FAST-negative patients
who showed no clinical sign of intra-abdominal trauma, which suggests
that performing CT in this group would incur unnecessary cost and risk
from ionising radiation, while showing no benefit to the patient.
A negative FAST scan was an excellent
predictor of the absence of significant intra-abdominal injury. While
the mortality rates of patients in the FAST-negative group was
disconcertingly high, the cause of death, after thorough chart review,
was not attributable to missed injury. Two missed injuries that were
found on CT (i.e. a splenic contusion and a minor renal laceration) did
not require operative intervention and were successfully managed
conservatively. There were 2 injuries in the FAST-negative group that
received a laparotomy: a bowel injury that was missed on CT and a
diaphragmatic hernia that was found on screening chest radiography.
These injuries must be kept in the differential for any patient who
sustains blunt abdominal trauma, but do not obviate the triage
algorithm in question.
CT showed the presence of free fluid in 80%
of FAST-positive patients, with free fluid or blood in the peritoneal
cavity found at laparotomy in 91% of FAST-positive patients, confirming
the superior sensitivity of ultrasound to CT for detecting the presence
of free fluid.
Limitations
The study has several limitations that limit the generalisability of the findings: (i)
it is a retrospective analysis. Many of the traditional biases incurred
by retrospective analyses are therefore applicable here; (ii)
the study was developed without strict guidelines of how to categorise
outcome. The process of categorising the cause of mortality did not
utilise predetermined criteria, which limits its scientific validity.
In addition, the chart review process and the morbidity/mortality
attribution process was performed by separate authors; (iii)
the study was designed and carried out within the span of a month in a
country with numerous logistical, cultural and language barriers. While
various omissions were included at a later point via email
communication with on-site personnel, this also incurred limitations; (iv) patients were not followed up after discharge or transfer to determine if any missed injuries presented at a later stage.
Future direction
This study should be repeated in a
prospective, randomised manner, where the control group is triaged
according to current protocol and an intervention group receives
abdominal CT. In that way, one could determine which injuries are
missed according to the current protocol, and if locating these
injuries would improve patient outcome. The triage pathway needs to be
more rigorously delineated, information collected more objectively, and
outcome groupings given standard definitions. In addition, patients
should be contacted at a defined, future point and interviewed using a
systematic questionnaire to provide delayed outcome information.
Ethics
approval was obtained from the University of Stellenbosch Research
Development and Support Department Committee for Human Research;
Project Number N08/10/295, IRB Number IRB0005239. This paper was an
oral presentation at the EMSSA Emergency Medicine in the Developing
World Conference in Cape Town, on 25 November 2009.
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Fig. 1. Diagram showing triage pathways for patients with blunt
abdominal trauma. Patients with stable vital signs and no sign of
intra-abdominal injury underwent serial FAST and physical examination
without undergoing CT. Patients with positive FAST scans received CT if
they remained haemodynamically stable. At any point in the triage
pathway, unstable patients underwent immediate exploratory laparotomy.
Fig. 2. Main results for the whole group, and breakdown for FAST-positive and -negative clinical outcomes.
Fig. 3a. Positive FAST in a 31-year-old male patient involved in a
pedestrian-motor vehicle accident shows free fluid in the hepatorenal
recess (RLIVER=right liver lobe, FF=free fluid, RK=right kidney).
Fig. 3b. Ultrasound for comparison of a normal hepatorenal recess
(Morrison’s Pouch) demonstrating the absence of free fluid between the
right liver lobe (black arrow) and right kidney (white arrow).
Fig. 4. Axial CT of the abdomen at the level of the superior liver
segments, in the same patient whose images appear in Fig. 3, shows a
grade IV liver laceration (white arrows) with free fluid surrounding
the liver.
Fig. 5. CT oblique coronal reformat of the same patient whose images
appear in Figs 3 and 4 shows free fluid in the hepatorenal recess
(white arrow) with free fluid surrounding the liver.