Blunt abdominal trauma - handout
Jen Nicol PGY-2
Staff: Dr. Lafreniere
August 5, 2010
Pathophysioloy:
The most common mechanisms of blunt abdominal trauma (BAT) are motor vehicle collision (50-75%);
followed by direct blows to the abdomen (15%), then fall from height (6-9%). The subsequent intra
abdominal injuries (IAI) injuries occur by 3 types of forces:
1) Increase in intra-abdominal pressure - sudden and pronounced exerted by outward forces,
resulting in burst or rupture of hollow viscus.
2) Compression – organs compressed between anterior abdominal wall and posterior thoracic
cage/vertebral column. The net effect is crush, solid organs more susceptible. This mechanism is
exaggerated in patients with weak abdominal walls (elderly, alcoholics)
3) Acceleration/deceleration – From abrupt stop from a rapid speed. Solid and hollow organs,
increased susceptibility if organ fixed in place, vascular structures.
(1) Physical Exam
The initial assessment of history and physical exam may range from reliable to incomplete or impossible.
Many BAT patients present to emergency department with EMS intoxicated, agitated from a head
injury, both of the above, or intubated secondary to airway compromise, low GCS. These factors render
the physical exam difficult to perform and interpret. Even in the alert, non-intoxicated, and GCS 15
patient there are often other injuries distracting the patient and clinicians from possible intra abdominal
injury. The accuracy of physical exam in BAT is approximately 55-65%, depending on which study you
are looking at.
Many of the studies examining the physical exam in BAT quote the following as the most reliable
symptoms and signs of intra abdominal injury in BAT in the alert patient:
1) Pain
2) Tenderness with guarding (present in 75% of patients with positive findings)
3) Peritoneal findings
A large chart review of a 7 year period in a large New Orleans Hospital (Davies et. al. Ann Surg.
1976;183:672) n=437 BAT patients treated by gen surg, looked at the diagnosis of IAI in BAT. On physical
exam, they found that 75% of all patients had guarding and tenderness, and rebound/rigidity were
present in 28%. Upon initial assessment, however, 43% of total patients had no specific symptoms of
signs of IAI. Of these 43% asymptomatic, 44% went on to have an exploratory laparotomy, with 34%
found to have IAI (3/4 positive laps). This highlights the difficult nature of physical exam in BAT; in this
study more than one third of asymptomatic patients were found to have an IAI.
A normal exam in isolated abdominal injuries can be reliable, indicating a high negative predictive value.
The utility of a normal exam decreases with more severe, multisystem trauma, and patients with a head
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injury. An equivocal exam is not reliable and must be further investigated (Shurink et al. Injury.
1997;28:261).
In summary, the abdominal exam is not necessarily a reliable tool to assess BAT. Exams may be initially
normal in injured patients, then become abnormal as the injury progresses. This highlights the need for
repeated assessments by the same practitioner, and the use of diagnostic adjuncts.
Seatbelt Sign
The seatbelt syndrome consists of visceral and musculoskeletal injuries associated with the use of a
seatbelt. These injuries were noticed soon after the implementation of restraint devices. The hallmark of
seatbelt sign is contusion to the chest, neck, or abdomen, in vertical or horizontal lines corresponding to
the location of the seatbelt. Most common characteristics:
1) Neck:
a. injuries to the carotid artery, larynx, and c-spine.
2) Thorax:
a. sternal, rib, and clavicular fractures
b. cardiac, thoracic aorta injuries
3) Abdomen:
a. Lumbar spine fractures, Rib fractures
b. Mesenteric tears, intra-abdominal hollow viscus perforation
Think about the mechanism; a crushing force exerted by external force, with rapid deceleration.
(Velmahos et al. Amer Surg. 199;65:181) Prospective study examining seatbelt associated injuries.
Examined 410 restrained MVC trauma patients at two tertiary trauma centres in LA, comparing the
injuries associated with the 77 patients with seatbelt signs and the 323 patients with no seatbelt sign.
The patients with seatbelt sign had a significantly higher rate of injuries of any type (73% vs. 59%
p=0.04). 23% of patients with seatbelt signs of the abdomen had significant associated injuries
compared to 3% of patients with no seatbelt signs (p<0.0001). A significant injury was defined as an
injury requiring surgical intervention. No correlation between the intensity of the seatbelt mark, or the
body habitus to severity of injury. Another study found that 36% patients with an abdominal seatbelt
sign vs. 3% without to have small bowel perforations (Am Surg 1997;63:885)
Patients presenting with seatbelt signs of any type (neck, abdomen, thorax) should increase your
suspicion that there has been a significant injury of any organ system. A seatbelt sign of the abdomen is
associated with more serious and frequent intra-abdominal injury. Its presence should raise the
question a bowel injury, which occurs much more frequently than in the absence of an abdominal
seatbelt sign.
Chance Fracture
Chance’s fracture is a vertebral fracture, usually of the lumbar spine involving the posterior spinous
process, pedicles, and vertebral body. It is caused by simultaneous flexion and distraction forces on the
spinal column resulting in failure of the anterior, middle and posterior columns. Up to 50% of chance
fractures are associated with intra abdominal injuries, and are often seen in the context of lap belt use,
where the belt is worn to incorrectly to high above the pelvic bones. It can also be seen in 3 point
restraints when the shoulder strap is not used properly. A pitfall of chance fracture is misdiagnosing
these for compression fractures, and potentially missing associated abdominal injuries. Diagnosis best
made by CT T/L reconstructions.
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(2) Diagnostic Modalities
The diagnosis of injury in BAT is challenging. It is complicated by the fact that there are numerous
diagnostic tools available, but it is not always clear which one is appropriate to use in a given
circumstance. Each modality has its own advantages and disadvantages. Our goal as emergency
physicians is to minimize missed injuries, and make accurate diagnoses with the least amount of risk to
the patient. We also want to reduce morbidity and mortality and provide our patients with the best
outcomes possible. One of the biggest challenges is not to determine the presence of organ damage, but
rather to precisely exclude intra-abdominal injury.
Aside from standard laboratory tests, there are 3 main diagnostic modalities included in most algorithms
for BAT: FAST, CT, and DPL. When considering any test, need to think about these 3 questions:
1) Is the tool precise and available at a reasonable cost?
2) Can the pretest in any patient with the target disorder be reasonably estimated?
3) Will the post test probability after the test change therapeutic action?
FAST: Focused Assessment with Sonography for Trauma
U/S use in trauma was first described in 1968. Since then it has grown exponentially and is now used
worldwide in the setting of trauma. Aim is to detect or exclude free intraperitoneal fluid, indicating
organ injury. It is often used in the initial assessment of BAT.
Advantages:
 easy to execute
 rapid results, no waiting for interpretation
 repeatability
 expedite disposition of unstable patients to laparotomy
 serial exams
 Detect small amount of free fluid – from 10-25cc close to lacerated viscera, however most
studies quote >200cc
 Readily available at the bedside.
 No complications
 Cost effective.
Disadvantage:
 Intra-abdominal injury is not always accompanied by free fluid (absent in 5-37%)
 Does not detect retroperitoneal, bony structure injuries
 Wide range of consensus for sensitivity and specificity.
 Negative FAST with a high test probability not always helpful.
 Poor performance in pelvic fractures
 Limited with obesity, ascites, subcutaneous emphysema
Sensitivity & Specificity
Generally, FAST has been shown to have good specificity (SP), but is limited by a lower sensitivity (SN).
These variables are not consistent among studies. A meta analysis looking at FAST (Br J Surgery
2001;88:901) found SN from 44-97% to detect intra-abdominal injury, and 28-90% to detect free
peritoneal fluid. There is an obvious trend that FAST is less sensitive in picking up mesenteric and small
bowel injuries. SP was uniformly high, consistently >90%. This means that a positive FAST is highly
suggestive for the presence of intraperitoneal injury, whereas a negative sonogram fails to confidently
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exclude traumatic organ lesions. This presents a dilemma, because identifying injury is arguably less
challenging with an emergency medicine team. Ruling out injury can prove to be more difficult, and have
implications on outcomes and patient flow through the emergency department and hospital.
Utility:
Positive FAST
 The clinical value of a positive test in most settings is clear
 A positive FAST can triage an unstable patient directly to the operating room or angiography
suite without any additional investigations.
 In more stable patients it can identify the presence of intra-abdominal injuries that can be
further characterised by CT.
 Many studies have looked at non-therapeutic laparotomy following FAST, and they reveal
consistently low false positives, comparable to that of CT.
Negative FAST:
 Negative FAST is more complicated to manage, because of the lower sensitivity, and the
possibility of a false negative study.
 A negative FAST must be interpreted with the clinical context of the patient. If negative and you
have a very high pre-test probability, then further assessment is required.
 If the patient is unstable and the FAST is negative, the abdomen must be re-assessed
continuously during the resuscitation as a source of blood loss.
 (Radiology 2004;230:661) a retrospective study looking at outcomes of negative U/S in the
trauma bay. The ultrasound technique used was not FAST, but rather a study performed at the
bedside by a technologist, interpreted immediately by a radiologist. This is the only study of this
nature that I found, and we can extrapolate the utility of FAST to this study.
o 99% true negative; 93.6% no further investigations and 6.4% went on to require further
investigations, all of which were negative.
o 1% false negative rates: 38 patients with 65 injuries were missed. (most common in
order were retroperitoneal hematoma, spleen and liver lacerations, renal, adrenal, and
small bowel injuries).
o Out of those missed, clinicians were alerted to reassess the patient by the following
signs/symptoms:
Pain
20
Hematuria
8
Decreasing hematocrit levels
5
Abdominal wall ecchymosis
4
Hypotension
3
Rib, spine, or pelvic fractures
3
Other clinical indication
2
o The mean time to diagnosis of missed injury was 16.8 hours.
FAST and Outcomes:
Ultrasound-based algorithms are often presumed to shorten the primary trauma assessment, triage
patients more precisely, and avoiding unnecessary interventional procedures and investigations like CT
and DPL. Does FAST really do all this?
A recent Cochrane review ()looked at ultrasound based algorithms effect on rates of laparotomy, CT,
DPL, and on patient outcomes. This is a summary of their findings:
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CT scan ordering: decreased by 50% with FAST
Delayed diagnosis: 60% reduced RR of delayed diagnosis (one study identified)
Door – OR time: significantly shorter
DPL: decrease by 6%
No difference in length of ICU stay
No decrease in mortality
No decrease in laparotomy (other studies have shown no increase either)
The SOAP-1 study also looked at outcomes, and found decreased hospital length of stay and decrease
cost (we can extrapolate to system cost in Canada) with the routine use of FAST in their algorithms
compared to control.
FAST in pelvic fractures:
9% of BAT patients have pelvic fractures, and the mortality rate approaches 50% in hemodynamically
unstable patients. The sources of life-threatening bleeding are two-fold, from intra-peritoneal and
retroperitoneal structures. Bleeding from the abdomen requires laparotomy, while bleeding from the
retroperitoneum mandates angiography and embolization. Decisions about where to send patients from
the emergency department are difficult, and must be made emergently in these patients.
The sensitivity of FAST in pelvic fractures is overall decreased to detect free intraperitoneal fluid. The SN
is approximately 81% and SP 87% (J trauma 2006;61:97) to detect any free fluid in the context of pelvic
fractures. It does also not differentiate between hemoperitoneum and uroperitonemum. FAST is the
first screening tool used in the approach to the unstable patient with a pelvic injury, and is utilised to
triage the patient to the OR or to angio/pelvic fixation. The low SN/SP is thought to be attributable to
distorted retroperitoneum from fracture and hematoma, as well as leakage of retroperitoneum and
urine which confuse results.
CT Scan:
(AKA CAT scan – computerised axial tomography)
Advantages:
 Evaluates retroperitoneum
 Identify IPH
 Good at predicting operative lesions
 Characterise location and extent of organ injury
 Examines the spine and other bony structures
 Urinary tract injuries
 Demonstrates active extravasation appropriate for embolization
 Guide non-operative management for solid organ injury
 Can combine with scans of chest to evaluate cardiac and pulmonary structures
Disadvantages:
 Requires stable, cooperative patient
 Transport out of resuscitation area
 Radiologist interpretation
 Poor sensitivity for hollow viscus, diaphragm, pancreas, and mesenteric injuries
 Significant exposure to radiation – future risks not fully known
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Sensitivity and specificity
There are numerous studies looking at CT, and have found SN from 92-98% and SP up to 99%. For small
bowel and mesenteric injuries, the SN is slightly lower, at 88% , and for diaphragmatic injuries the SN
ranges from 54-73%.
Free Fluid Dilemma:
In the context of a solid organ injury, free fluid is attributable to bleeding from the injury site. However,
if the only finding on CT is free fluid with no other injury, this may signify one of 3 things: undetected
solid organ injury, bowel injury, or mesentery injury that may not necessarily require a laparotomy. This
is important because the mortality rate of missed hollow viscus injuries is as high as 31%, more so if not
diagnosed within 24 hours. This presents the dilemma of what to do in a stable patient with free fluid on
CT with no identified intra-abdominal injuries? A systematic review on the subject (J trauma 2002;53:79)
found an incidence of this problem to be 2.8% of CT scans in BAT, with a range of 0.6-4% in the
individual studies. The overall therapeutic laparotomy rate was 27% of all performed, which is not high
enough to mandate therapeutic laparotomies. If this was the case 73% would be non-therapeutic;
conversely, if no lapatoromies were performed then 27% would have missed diagnoses. Seatbelt sign
and larger amount of free fluid (greater number of slices with fluid) are more predictive of a positive
laparotomy. The review concludes that stable patients with free fluid in the absence of other findings
don’t require laparotomy, but should be observed, with serial exams. If altered mental status i.e. head
injury or intubated, they recommended DPL. It is unclear what the exact next step should be, but there
is enough evidence to suggest that an urgent laparotomy is not required.
A pediatric prospective observational study n=537 () found that 8% had isolated free intraperitoneal
fluid. Of these children, 17% (7) were identified during hospitalisation to have intra-abdominal injuries.
Patients with small amount of free fluid, no abdominal tenderness, and normal level of consciousness
were at lowest risk for subsequent injury. The authors concluded these children can be considered for
discharge.
The Negative CT scan:
The debate over the negative CT scan is ongoing, and is important because there is sometimes a
misconception that a CT scan can “rule out everything”. The main fear of foregoing an admission for
observation is that significant injuries will be missed, such as duodenal or hollow viscus perforation.
There are numerous studies with very low false negative rates on CT, but do not comment on how this
relates to management. A prospective, multi-institutional study from the trauma services perspective
concluded that adult trauma patients with normal abdominal CT scans can safely be discharged from the
emergency department (J trauma 1998;44:273). The 4 study sites enrolled consecutive patients over a 2
year period, and concluded that a negative CT on a preliminary interpretation (radiology resident,
trauma surgeon) had a negative predictive value of 99.63%. There were 4 missed injuries out of 2082, 2
jejunal perforations and a retroperitoneal hematoma, diagnosed while still in hospital. A sigmoid colon
perf was diagnosed when the patient returned with abdominal pain after discharge. 97% of these
patients had other extra-abdominal injuries, which may or may not on their own prompted admission (it
does not include this detail in the study).
A recent pediatric study (Academic Emerg Med 2010;15:89) examined the same in the pediatric
population. They found a NPV of 100%. Of their study population (n=1085) 32% were discharged home
and 68% were admitted for observation or management of other extra-abdominal injuries. None of the
patients discharged home and 2 of the admitted patients had an identified intra abdominal injury (1
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non-operative perinephric hematoma, 1 bowel contusion with a non-therapeutic laparotomy in an 11 y
F with a seatbelt sign)
Can we conclude that every patient with a normal CT scan can be discharged from hospital? No, but
these studies support our decisions when we do decide to discharge patients from the emergency
department. The decision to discharge must be based on a number of factors, including concurrent
injuries, any impairment in judgement (i.e. intoxication, minor head injury), mechanism of injury, and
how concerned we are of an underlying intra-abdominal injury.
DPL
In our approach to trauma today, with numerous new or more effective diagnostic tools, DPL has fewer
indications for use in the trauma bay. FAST has largely replaced DPL in the initial search for intraabdominal injury. The main indication for DPL is triage of the multiply injured unstable patient with an
equivocal or even negative FAST. In comatose or seriously head injured patients DPL is sometimes used instead of
serial exam to rule out intra-abdominal hollow viscus injuries.
Advantages:
 Relatively quick bedside procedure with low complication rate
 Useful in difficult situations (above) where FAST is not helpful in an unstable patient
Disadvantages:
 While <2% (0.3-0.8% in large case series), complications do occur, including perforation,
bleeding, and subsequent infection (injury 2000;31:479)
 More time intensive than FAST
 More sensitive than CT for diagnosis of mesenteric injury
 False positive results: Insertion through abdominal wall hematoma, pelvic fractures
 False negatives: placement into pre-peritoneal space, adhesions compartmentalising fluids,
obstructing omentum and diaphragmatic injury.
Interpreting DPL
This lecture is not meant to cover how to perform DPA / DPL, this is covered in ATLS and in the advanced
procedure lab that we do. Very briefly, there are 2 techniques, open and closed. Open involves actually
visualising the peritoneum, whilst the closed technique utilises the blind percutaneous method of the
Seldinger technique.
The first step is aspiration of peritoneal fluids. A positive result is aspiration of >10ml frank blood, which
has a 90% positive predictive value for intraperitoneal injury. This represents 80% of positive DPL’s. The
next step is lavage of the fluid. RBC > 100,000/mm3. Indeterminate is 20,000 – 100,000/mm3. Escape of
fluid through a foley catheter or thoracostomy tube are positive signs of bladder and diaphragmatic
injuries, respectively. WBC count, amylase, and bile in the lavage are non-specific and generally not
useful.
Contra-indications to DPL:
 Absolute: established need for laparotomy
 Relative:
o Prior abdominal surgery
o Infections
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o
o
o
Coagulopathy
Obesity
2-3rd trimester pregnancy
Sensitivity and Specificity:
DPL is very accurate, with reported SN between 87-95%. It is also specific, between 97-99%. Accuracy
has been described at 92-98%. There are a higher number of false positives in pelvic fractures, due to
tearing of retroperitoneum or leakage of retroperitoneal blood into peritoneal space.
DPL and Diaphragm Rupture
Diaphragm injury occurs in up to 5% of injuries to the thorax or abdomen, and diagnosis is missed or
delayed in up to 50%. When made early after the trauma, diagnosis is by obvious CXR findings, or at
laparotomy for other associated intra-abdominal injuries. False negatives in DPL occur as lavage fluid
exits the peritoneal cavity into the thorax. In one case series in the 70’s (J trauma 1976;16:538) when
DPL was commonly performed in BAT, 34/38 patients with a diaphragm injury underwent DPL, which
was negative in 29%. Four of these patients had significant intraperitoneal hemorrhage that was missed
by false negative DPL. All isolated diaphragmatic ruptures were negative. DPL in this series that were
initially positive with diaphragmatic rupture occurred with significant intraperitoneal hemorrhage from
injury to other organs. In this series, 90% of patients with diaphragmatic injuries suffered concurrent
injuries to the abdomen.
As aforementioned, CT also has poor sensitivity to diagnose diaphragm injury, and FAST had shown to
miss injuries that occur in the absence of free fluid. This presents a challenge in the diagnosis of
diaphragm injuries, and a low index of suspicion must be maintained in patients presenting with a
significant mechanism in BAT.
(3) management Principles in BAT:
The basic premise of managing BAT is the maintain the following goals in a timely manner:
 Stabilize the patient
 Determine presence of intraperitoneal hemorrhage
 Demonstrate organ injury requiring operative intervention
 Don’t miss injuries!
QUESTION: Clinical indications for laparotomy
1) Unstable VS, strongly suggestive abdominal injures
2) Unequivocal peritoneal irritation
3) Evidence of diaphragmatic injury
4) Significant GI bleeding
There are numerous algorithms applied to help in BAT. Some use FAST, some use DPL, but all have the
basic framework of identifying unstable and operative patients.
(4) Hematuria in BAT
Of all injuries to the genitourinary system in blunt trauma, the kidneys are most commonly involved. The
gross majority of injuries are stage 1 (renal contusion), which require no further management, and stage
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2-5, which require additional testing and follow up by urology, make up 5% of blunt renal trauma. It
therefore makes sense that the goal should be to identify patients with a greater likelihood of significant
renal trauma without subjecting the remainder to unnecessary and potentially harmful diagnostic
procedures.
Hematuria is the best indicator of traumatic injury to the urinary tract. It must be obtained from a first
catheter or void specimen, as subsequent samples are diluted during resuscitation. A positive urine
dipstick has been shown to have a specificity and sensitivity of 97 %. Microscopic hematuria is defined
as a positive dipstick or >5RBC’s /HPF. Gross hematuria is visible blood of any degree.
The degree of hematuria and severity of renal injury do not consistently correlate. How do we know
should undergo imaging for renal injury? The largest series looking at renal trauma and hematuria has
been ongoing for 25 years and has had 3 updates since the start (J urol 1995;154:352). They have found
that patients with blunt abdominal trauma and hematuria should be imaged only if:
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Gross hematuria
Microscopic hematuria in the presence of shock (SBP <90)
Significant deceleration injury
Other intra-abdominal injuries that require imaging.
Microscopic hematuria in the absence of shock can be monitored clinically, and do not need urgent
imaging. With this protocall (n=1588 BAT), they have not missed any significant renal injury requiring
intervention, nor renal vascular injuries which have been found to occur in the absence of hematuria.
The imaging of choice is a CT scan with IV contrast. (Note: in the low risk group, the CT scans that were
ordered were performed for concern of other intra-abdominal injury or at the discretion of the
emergency physician).
Pediatrics: are they just little adults?
There is less consensus when to image for renal injury. A large retrospective study to validate the adult
prediction rules in pediatrics found that no clinically significant injuries would be missed applying the
criteria above (J Urol 2004;171:822). They also re-analysed the data from previous studies on the subject
and found that at most 2 significant injuries would have been missed out of a pooled 382 patients. A
caveat to the adult rule is that hypotension is not a good marker of shock in children, and that serial
haemoglobin is best followed instead.
(5) Pitfalls in BAT: (Emerg Med Clin N Am 2010;28:1)
1) False negative Prediction: an inappropriately high negative predictive value is given to a physical
finding, lab result or imaging study (i.e. abdomen is soft, non tender therefore there is no intraabdominal injury; the CT scan is negative so there is no injury). On ititial assessment, most exam
findings and diagnostic modalities are not good enough to rule out injury on initial assessment.
2) False attribution: wrongly attributing a physical sign or result to something unrelated. Ie BP is
low, because of a vasovagal instead of the intra-abdominal hemorrhage that is developing.
3) Failure to assess the abdomen and pelvis. This has been recognised as the most common error
in trauma management. The most serious errors occur when the abdomen is overlooked all
together. To avoid this, take a good history if the situation permits, do a thorough exam of the
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abdomen keeping a high index of suspicion, and use your imaging modalities liberally, within
reason.
4) Missed injuries: Blunt intestinal injuries have a miss rate of up to 14%, and blunt pancreatic is
significant too. This is difficult, because as metioned above the initial CT can be falsely negative.
This highlights the need to reassess patients and not underestimate the onset or worsening of
abdominal pain or physical findings.
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