Emergency ultrasound in adults with abdominal and thoracic trauma

INTRODUCTION — Since its appearance as a diagnostic tool during World War II, ultrasonography has gained an increasingly important role in the assessment of the trauma patient. The term "Focused Abdominal Sonography for Trauma" was coined in 1996 to describe a standard set of ultrasound examinations for the evaluation of injured patients. The meaning of the acronym was changed to Focused Assessment with Sonography for Trauma (FAST) a year later to reflect applications outside the abdomen.

The performance and interpretation of ultrasound examination in the patient with abdominal or thoracic trauma will be reviewed here. Trauma management, including management of abdominal and thoracic injuries, is discussed separately.

●(See "Initial management of trauma in adults".)

●(See "Initial evaluation and management of blunt thoracic trauma in adults".)

●(See "Initial evaluation and management of penetrating thoracic trauma in adults".)

●(See "Initial evaluation and management of blunt abdominal trauma in adults".)

●(See "Initial evaluation and management of abdominal gunshot wounds in adults".)

●(See "Initial evaluation and management of abdominal stab wounds in adults".)

FOCUSED ASSESSMENT WITH SONOGRAPHY FOR TRAUMA

Overview — Ultrasound provides an important initial screening examination in the adult trauma patient. However, ultrasound is not a replacement for the more sensitive imaging studies often needed to identify specific injuries in patients with concerning abdominal or thoracic symptoms or signs. Most such patients, if hemodynamically stable, undergo computed tomography (CT). Unstable patients with intraperitoneal hemorrhage identified by ultrasound generally proceed directly to laparotomy.

For unstable patients without an obvious source of bleeding and in whom the initial ultrasound examination is negative (ie, without intraperitoneal fluid), a diagnostic peritoneal tap, or angiography, may be needed depending upon the clinical scenario. As an example, ultrasound generally plays a more limited role in the evaluation of patients with significant pelvic fractures because it is less sensitive for detecting pelvic bleeding, cannot detect retroperitoneal bleeding, and cannot differentiate between blood and urine. The management of such patients is discussed separately. (See "Pelvic trauma: Initial evaluation and management", section on 'Initial management'.)

Ultrasound evaluation performed as part of the initial examination and resuscitation of the trauma patient is known as the Focused Assessment with Sonography for Trauma (FAST) [1,2]. The extended FAST examination (E-FAST) is used when views are added to evaluate for pneumothorax.

The primary purpose of the FAST examination is to determine the presence of pathologic pericardial, intrathoracic or intraperitoneal free fluid, which appears as a hypoechoic or anechoic (ie, dark grey or black) collection, or the presence of pneumothorax. The sole contraindication to the FAST examination is the need for immediate surgery. In addition, decreasing the time required for the initial evaluation of trauma patients, as well as limiting exposure to ionizing radiation, continues to be an important goal in trauma management. The E-FAST is being studied as a potential tool allowing for the omission of supine radiographs when CT imaging is to be performed, without sacrificing diagnostic accuracy [3,4].  

The major interrogations that comprise the E-FAST examination use established views (or windows) to evaluate the pericardial, peritoneal, and pleural cavities. The standard order of evaluation is as follows:

●Pericardial (picture 1 and image 1 and image 2)

●Right flank (hepatorenal view or "Morison's pouch") (picture 2 and image 3)

●Left flank (perisplenic view) (picture 3 and image 4 and image 5)

●Pelvic (retrovesical views) (picture 4 and picture 5 and image 6)

●Thoracic (pneumothorax (picture 6 and image 7) and hemothorax evaluations (image 8))

Following this progression helps to ensure that pericardial tamponade, the most acute, life-threatening injury among those identifiable by ultrasound, is found first and that elements of the examination are not inadvertently omitted. Nevertheless, in some cases the order of the interrogations may be changed depending upon the mechanism of injury and intraperitoneal fluid dynamics. The dynamics of fluid flow within the peritoneum and how this might affect the order of the ultrasound examination are discussed below. (See 'Intraperitoneal free fluid' below.)

If time permits, skilled ultrasonographers can perform a more extensive ultrasound examination, including detailed assessment of solid organs, but this is not ordinarily included in the emergency department (ED) evaluation of the trauma patient.

According to the guidelines of Advanced Trauma Life Support (ATLS), the FAST examination is typically performed during the "C" portion of the primary survey during the assessment of circulation and hemorrhage. By convention, a low frequency (2.5 to 5 MHz) curvilinear or phased array probe is used to allow for appropriate viewing depth when performing the FAST. The primary and secondary surveys of the trauma evaluation are described separately. (See "Initial management of trauma in adults".)

FAST versus other diagnostic techniques — Ultrasound is easy to use, portable, noninvasive, inexpensive, and does not expose the patient to ionizing radiation. Furthermore, ultrasound examinations are easily repeated at the bedside, thereby enhancing clinicians' ability to perform serial reassessments of trauma patients [5].

In contrast, diagnostic peritoneal tap and diagnostic peritoneal lavage (DPL), while highly sensitive for intraperitoneal hemorrhage, carry a 1 to 2 percent complication rate and are not ordinarily performed in the stable patient. CT is highly sensitive for both intraperitoneal hemorrhage and solid organ injury and is the imaging study of choice in stable patients with suspected intraabdominal or intrathoracic injury. However, in some hospitals, CT requires that patients be transported out of the resuscitation suite (which is usually contraindicated in unstable trauma patients), exposes patients to ionizing radiation, and entails higher costs. The use of DPL and CT in blunt abdominal trauma is discussed separately. (See "Initial evaluation and management of blunt abdominal trauma in adults", section on 'Computed tomography' and "Initial evaluation and management of blunt abdominal trauma in adults", section on 'Diagnostic peritoneal lavage'.)

Limitations of FAST — Limited sensitivity precludes the use of ultrasound as a definitive test to rule out intraabdominal injury [6]. In most studies, the sensitivity of the FAST examination for intraperitoneal hemorrhage ranges from 63 to 100 percent [7-11]. However, sensitivities as low as 42 percent have been reported [12]. If significant injury is suspected and the FAST examination is negative, the hemodynamically stable patient requires further imaging (usually CT) because injuries requiring operative management may otherwise be missed [13].

FAST examinations can give false negative results. In one large retrospective study using data collected prospectively for a trauma database, the overall false negative rate of the FAST examination was below two percent, but 23 percent of these patients (10 of 43) required operative intervention [9]. In a similar study, 157 patients with an intraabdominal injury had no free fluid detected by ultrasound, but 26 of these patients (17 percent) required surgery or angiography [6].

A number of injuries are not detectable by ultrasound. The FAST examination cannot discern diaphragm tears, pancreatic lesions, bowel perforations, mesenteric trauma, and abdominal injuries that do not produce free fluid in amounts detectable by ultrasound (generally >200 mL) [10,14,15]. The ability of ultrasound to detect injuries to the kidney and other retroperitoneal structures is limited. Moreover, ultrasound cannot distinguish between urine and blood, which contributes to its lower sensitivity and specificity in major pelvic trauma [16,17]. (See "Pelvic trauma: Initial evaluation and management".)

Ultrasound is limited by patient comorbidities. As examples, accurate cardiac or abdominal images may be difficult to obtain in patients with severe obesity or subcutaneous emphysema. Hyperinflated lungs from chronic pulmonary disease may reduce the accuracy of cardiac images.

Improving FAST — Each FAST examination reflects the clinical picture at one moment. The overall sensitivity of FAST for abdominal injury can be improved by using serial ultrasound examinations. According to one prospective observational study of 547 blunt trauma patients, a second ultrasound examination performed within 24 hours improves sensitivity, negative predictive value, and accuracy for intraabdominal injury [18]. Another observational study reported a sensitivity of 94 percent for detecting significant abdominal injury when combining a negative FAST examination with a 12-hour period of observation, including reassessment with ultrasound or CT for any patient who "deteriorated clinically" [7].

PERICARDIAL AND LIMITED CARDIAC EXAMINATION

Hemopericardium — The detection of pericardial fluid is the key element in the ultrasound examination of the heart and pericardium in trauma. Fluid that accumulates between the visceral and parietal pericardial layers appears as a dark anechoic stripe (image 2). In addition, the heart is assessed for the presence of cardiac tamponade, global wall motion abnormalities and other evidence of injury, and the adequacy of right ventricular filling. The following video clips show normal cardiac motion and tamponade (movie 1 and movie 2 and movie 3).

Clinicians must take care not to confuse epicardial fat pads with true pericardial effusion (image 9) [19]. Movement is an important distinguishing feature: epicardial fat pads are attached to the heart and move with it as the heart contracts; pericardial effusions or blood clots within the pericardium do not move with the heart. (See "Cardiac tamponade" and "Emergency pericardiocentesis".)

To reduce the risk of false negative examinations of the pericardium in the setting of penetrating thoracic trauma or hemothorax, we recommend that the pericardial ultrasound examination be repeated after any hemothorax is cleared by chest thoracostomy. False-negative examinations remain possible despite such maneuvers if the hemopericardium empties into the thoracic cavity, thereby preventing blood from accumulating in the pericardium. (See 'Penetrating thoracic trauma' below.)

Subcostal view — Ultrasound evaluation of the cardiac region in trauma patients is often performed using a subcostal view (image 1). With this approach, all four cardiac chambers and the pericardium can be seen.

The subcostal view is obtained by placing either a curvilinear abdominal probe or a phased-array probe in the subxiphoid area (picture 1 and movie 1). The phased array probe, which emits sound waves sequentially, is better at capturing movement and is therefore optimal for obtaining this view. The probe is oriented transversely with the indicator pointed to the patient's right side and the surface of the probe directed toward the patients left shoulder. The body of the probe lies nearly flat on the patient's abdomen.

Obtaining adequate images using the subcostal view can be difficult in obese patients and patients with a large volume of stomach gas, a prominent xiphoid process, a narrow subxiphoid space, or a tender or distended abdomen. Alternative orientations, such as the parasternal long or apical four chamber views, can be used to obtain adequate images in patients whose subcostal view is incomplete.

Parasternal long view — The parasternal long axis (PSLA) view is the primary alternative when the subcostal approach provides an inadequate image of the heart. The PSLA view allows visualization (moving anterior to posterior) of the right ventricle (RV), interventricular septum (IVS), left ventricle (LV), left atrium (LA), and the descending aorta (image 10 and movie 4). Within the LV the mitral valve leaflets, chordae tendinae, papillary muscles, and aortic valve can be seen. In addition, the clinician can see small pericardial effusions, which appear as a thin anechoic fluid collection posterior to the LV. As the size of the effusion increases, it can be seen anterior to the RV.

The right atrium (RA) is not seen with the PSLA view. The RA is the chamber with the lowest pressure and would theoretically be the first to collapse with rising pericardial pressure due to tamponade. However, the PSLA view allows visualization of the most dependent portion of the pericardium in the supine patient.

To obtain the PSLA view, the probe is placed perpendicular to the surface of the chest in the fourth or fifth intercostal space left of the sternum with the indicator pointed towards the right shoulder (picture 7). The PSLA view may be improved by placing the patient in the left lateral decubitus position, which brings the heart closer to the chest surface.

The PSLA view may be difficult to obtain in patients with hyperinflated lungs from chronic lung disease or mechanical ventilation because ultrasound waves do not travel well through the tissue-air interface.

Apical four chamber view — The apical four chamber (A4C) view is another means of evaluating the heart in trauma. Using the A4C view, all four cardiac chambers can be seen, enabling the clinician to assess RV collapse, pericardial effusion and cardiac tamponade, and overall cardiac function (image 11 and movie 5 and movie 6 and movie 7). The most dependent portion of the pericardium cannot be seen on the A4C view, in contrast to the PSLA view.

The A4C view is obtained by placing the probe on the left chest between the midclavicular line and the anterior axillary line at the level of the nipple line or below the breast (approximately the fourth or fifth intercostal space), with the transducer oriented towards the right shoulder and the indicator pointed towards the patient's right side. Placing the patient in a left lateral decubitus position makes it easier to acquire the A4C view.

IVC evaluation and fluid status — A limited ultrasound of the heart may provide insight into the fluid status of the trauma patient, especially when a focused examination of the inferior vena cava (IVC) is performed in addition to the standard cardiac views. This examination involves measuring the diameter of the IVC at end expiration. If the IVC is not visualized, a hyperdynamic ventricle (ie, one in which the ventricular walls touch or almost touch at the end of systole) also suggests volume depletion. The use of ultrasound to assess fluid status is reviewed in greater detail separately. (See "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Point-of-care ultrasonography'.)

Assessment of the IVC is typically performed while the probe remains in the subxiphoid space after examining the heart using the subcostal view. The probe is rotated in a clockwise fashion from the standard subcostal orientation described above (picture 8). Once rotated, the probe lies in a sagittal orientation with the indicator pointed towards the patient's head. With the probe in this position, the IVC is seen in its long axis as it enters the right atrium (movie 8). The IVC diameter is assessed 2 cm distal to the point at which the hepatic vein or veins enter the IVC (image 12). In equivocal cases, the ultrasonographer can augment the examination by assessing IVC collapsibility. If the IVC collapses when the clinician compresses the IVC with the probe, this suggests volume depletion.  

ABDOMINAL EXAMINATION

Intraperitoneal free fluid — A major purpose of the Focused Assessment with Sonography for Trauma (FAST) is to identify free fluid in specific dependent locations within the peritoneal cavity. This fluid is presumed to be blood and a sign of injury, although it may represent urine in cases of pelvic trauma. In addition, small amounts of free fluid may be physiologic. (See 'Females of reproductive age' below.)

Free fluid typically appears as an anechoic collection (image 13 and movie 9). However, clotted blood may appear echogenic. If any view reveals an anechoic collection, the FAST examination is considered positive and injury is presumed [1]. The examination is considered negative only if all views are free of fluid. The study is indeterminate if any one view cannot adequately be assessed.

The detection and location of intraperitoneal free fluid depends upon several factors including [20]:

●Location of injury

●Time elapsed since the injury

●Presence of intraabdominal adhesions

●Bowel gas patterns

●Fluid volume

●Patient positioning

●Quality of the FAST examination

Gravity preferentially causes fluid to accumulate in the most dependent spaces within the peritoneal cavity. For the purposes of this discussion, the peritoneum can be divided into the upper peritoneal or supramesocolic space (between the diaphragm and the transverse mesocolon) and the lower peritoneal or inframesocolic space (below the transverse mesocolon).

The movement of intraperitoneal free fluid is determined by the source of the fluid (eg, location of injury), position of the patient, and anatomic constraints. The phrenicocolic ligament prevents fluid from flowing from the upper to the lower peritoneum via the left pericolic gutter [20]. Such fluid must transit via the right pericolic gutter to reach the lower abdomen. Thus, in a supine patient, intraperitoneal bleeding from an injured spleen must first travel through Morison's pouch (potential space between the liver and the right kidney) before entering the pelvis.

Conversely, fluid originating in the lower peritoneum collects in the pelvis and then travels to Morison's pouch. As an example, free fluid from an isolated pelvic injury (eg, stab wound) would accumulate first in the pelvis, then spread up the right pericolic gutter into Morison's pouch, and finally to the perisplenic area. In such a scenario, ultrasound examination of the pelvic space might reveal free fluid before other views. Note that Morison's pouch is either the first or second site of fluid accumulation, regardless of the location of an intraabdominal injury.

A number of studies have tried to determine the minimum amount of fluid needed to be detectable by ultrasound [14,21-23]. Results vary from approximately 620 to 670 mL in Morison's pouch to 160 mL in the pelvis [14,21,22]. When multiple views are used, some studies have found that ultrasound can detect approximately 200 to 250 mL of intraperitoneal free fluid. Of note, many of these studies were performed using an experimental model of diagnostic peritoneal lavage and their results may not apply to patients with blunt abdominal trauma.

Hemothorax — In the normal patient, the thoracic space contains lungs filled with air, which scatters the ultrasound signal. In patients with a pleural effusion, an anechoic stripe can be seen superior to the diaphragm, and often the border of the lung can be visualized as well, as seen in the following image and video clip (image 8 and movie 10).

The costophrenic area assessed as part of the FAST examination is the most dependent portion of the thoracic cavity in the supine patient and the site where free intrathoracic fluid accumulates. In the patient with thoracic or abdominal trauma, injury is presumed if intrathoracic fluid is seen. Nevertheless, it is sometimes difficult to distinguish between hemothorax and chronic or subchronic effusion using ultrasound, as either may contain free fluid, fibrin stranding, and clot. Depending upon the clinical circumstance, additional imaging (CT) or a procedure (eg, placement of a thoracostomy tube) may be needed.

Studies of the test characteristics of ultrasound for detecting traumatic hemothoraces are found below. (See 'Pneumothorax and hemothorax' below.)

Right flank view — The right flank is the first abdominal area examined as part of the FAST examination. Four spaces are evaluated including the pleural, subphrenic, hepatorenal (Morison's pouch), and the inferior pole of right kidney. The liver, the largest solid organ in the body, provides the sonographic window to visualize these spaces.

The right flank view is obtained by placing the probe between the midclavicular and posterior axillary lines in an intercostal space (most commonly the 10^th or 11^th), but may be performed subcostally after having the patient take a deep breath, which displaces the liver margin inferiorly (picture 2 and image 3 and movie 9). The probe indicator is pointed towards the patient's head.

The study is performed by fanning the probe from the anterior to the posterior abdomen, thereby systematically visualizing the entire region. It is often necessary to move the probe one or more rib spaces to a more rostral or caudal position in order to visualize the entire region from the lower thorax and diaphragm to the inferior portion of the liver.

Rib shadowing is a common problem when obtaining this view and may be minimized by moving the probe in a cephalad or caudad direction, rotating the probe slightly counter-clockwise (more parallel with the ribs), or having the patient breathe in or out to move the area of interest inferiorly or superiorly (away from the rib shadow) [1,24]. Angling the probe cephalad allows for visualization of the pleural and subphrenic spaces. Angling caudad allows for visualization of Morison's pouch and the inferior pole of the kidney.

Orthogonal views are not traditionally part of the FAST examination, but may be performed. Again, the study is performed by scanning from rostral to caudal orientations, systematically visualizing the entire region. By convention, the probe indicator is rotated from the head to the right of the patient (ie, pointed toward the bed when examining the right flank and toward the ceiling for the left flank).

Left flank view — Following the right flank examination, four spaces in the left flank are evaluated, including the pleural, subphrenic, perisplenic, and the inferior pole of the left kidney. The spleen provides the sonographic window to see the spaces of the left flank. Compared to the liver, the spleen is notably smaller and seated more posteriorly and superiorly.

To examine the left flank, the probe is typically placed posterior to or on the posterior axillary line in an intercostal space (most often the eighth or ninth) (picture 3 and image 4 and movie 11). The probe indicator is pointed towards the patient's head.

As with the right flank view, the probe is fanned from the anterior to posterior abdomen to visualize the entire region. Free fluid most commonly accumulates at the angle formed by the superior pole of the left kidney and the diaphragm, and it is important that this perisplenic space is interrogated in its entirety. The probe may be moved one rib interspace rostral or caudal for complete visualization.

Interference from rib shadowing is overcome in a fashion similar to the right flank views, keeping in mind that a slight clockwise rotation is required to orient the probe parallel to the ribs on the left side [1,24]. Angling the probe cephalad allows visualization of the pleural and subphrenic spaces while angling caudad allows visualization of the perisplenic space and the entire kidney.

Pelvic view — The pelvic region is the most dependent space in the supine patient and therefore an important site to look for free fluid [20]. The bladder provides the sonographic window for viewing the pelvis. While a partially filled bladder is generally adequate, an empty bladder does not permit visualization of small volumes of free fluid (image 6).

Observational studies suggest that a lack of bladder distention is a major reason pelvic free fluid is missed during the FAST examination [25]. If a bladder catheter (eg, Foley) has been placed, the bladder may be partially filled with isotonic saline to create a sonographic window. Approximately 200 mL can be used to fill the bladder of a stable patient, but this may be impractical during a resuscitation and smaller volumes may be used.

To obtain the pelvic view, place the probe in a sagittal orientation just above the symphysis pubis (picture 4). By convention, the probe marker is pointed toward the patient's head. The probe is moved across the entire bladder systematically, looking for fluid collections behind the bladder in males and behind the uterus in females [1,24]. The probe may be rotated counterclockwise 90 degrees into a transverse orientation for further examination of the pelvic peritoneum (picture 5).

PLEURAL EXAMINATION — The most dependent portions of the pleural spaces are typically evaluated using the standard flank views, as described above, and are useful for identifying hemothorax. However, separate pleural views using a higher frequency probe are needed to visualize a pneumothorax.

Instead of the standard (2.5 to 5 MHz) curvilinear or phased array transducer probe used for the basic FAST examination, a high frequency (5 to 10 MHz) linear transducer probe may be used to obtain optimal visualization of the interface between the visceral and parietal pleura of the lung. The field depth must be adjusted to a shallow setting (approximately 4 cm).

A variety of locations have been used to look for pneumothoraces with ultrasound, but there is no evidence to determine the best approach. Typically, the examination begins at the third or fourth intercostal space (ICS) at the midclavicular line with the probe indicator pointed cephalad (picture 6). Alternative examination locations include the second ICS at the midclavicular line, the fourth ICS at the midclavicular line, the fourth ICS at the anterior axillary line, the sixth ICS at the anterior axillary line, and the sixth ICS at the midaxillary line. Both the left and right lungs must be imaged.

In contrast to the rest of the FAST examination, the determination of pneumothorax does not depend upon the detection of anechoic free fluid. Instead, the examination focuses on visualization of the sliding of the pleura using either the gray scale b-mode, m-mode, or Doppler ultrasound. In addition, the lung is evaluated for the presence of "comet tails" that extend perpendicular from the surface to the deeper portion of the lung (image 7 and image 14). The comet tail sign is a reverberation artifact caused by areas of interstitial edema on the visceral pleura. The presence of sliding pleura and comet tails rules out pneumothorax in the region of the lung being examined. The lung point sign, the juxtaposition of lung sliding and the absence of lung sliding in the same space (representing the edge of a pneumothorax), confirms the presence of pneumothorax [26,27].

Studies describing the test characteristics of ultrasound for identifying pneumothorax are described below. (See 'Pneumothorax and hemothorax' below and 'Penetrating thoracic trauma' below.)

SPECIAL POPULATIONS

Females of reproductive age — Females of reproductive age often have a trace amount (approximately 5 to 20 mL) of free pelvic fluid [28]. Such fluid is associated with ovulation and generally considered physiologic. It has a reported prevalence of 36 to 40 percent and is often discovered on CT scan, although it can be seen with ultrasound [29]. Free fluid can confound the interpretation of a positive pelvic view obtained during the FAST examination. In general, we believe it is best to err on the side of caution and to assume that an injury exists when free fluid is found on the pelvic view in a female with abdominal or thoracic trauma.

The few studies that have evaluated free fluid in female trauma patients are all retrospective and report disparate results:

●A study of 1047 females of reproductive age with blunt abdominal trauma (BAT) found only one injury requiring surgical repair among the 56 females with fluid isolated to the pelvis [25]. Of the 939 patients with no free fluid, three had injuries requiring surgical intervention.

●Another study, involving 947 females of reproductive age with BAT, reported no difference in injury rates between those with isolated pelvic free fluid and those without free fluid [30]. Few injuries were identified in either group.

●Contradictory results were reported in a study involving 2319 females of reproductive age with BAT which found that isolated pelvic free fluid identified during the FAST examination was associated with a higher risk of intraabdominal injury compared to no free fluid in both pregnant and nonpregnant patients [28]. Seventeen injuries requiring surgical intervention were identified among 43 females with isolated pelvic fluid (40 percent) compared with 67 such injuries among the 1804 females with no free fluid (3.7 percent). Injury rates among females with abdominal or abdominal and pelvic free fluid were significantly higher (57 out of 70 [81 percent] and 67 out of 74 [91 percent] respectively).

Pregnancy — The initial management of the pregnant trauma patient is focused on establishing maternal cardiopulmonary stability. Displacement of a large uterus off the IVC is an important component of this process. Issues related to trauma resuscitation of the pregnant patient, including relevant physiologic changes in pregnancy, are discussed separately. (See "Initial evaluation and management of major trauma in pregnancy".)

When deciding upon imaging studies in pregnant patients, potential exposure of the fetus to the ionizing radiation and iodinated contrast involved in CT scanning must be considered. Imaging with ultrasound provides an alternative to CT, as well as information about the fetus, during initial trauma resuscitation. By combining the findings of serial ultrasound and physical examinations, it may be possible to avoid the need for CT. The issue of radiation exposure in pregnancy is discussed separately. (See "Diagnostic imaging in pregnant and lactating patients".)

Two retrospective studies have assessed the performance of ultrasound in pregnant trauma patients:

●A chart review of 101 pregnant patients with blunt abdominal trauma reported that screening sonography detected four of the five patients with injuries requiring surgical management [30]. The missed placental injury was detected 15 hours following the initial ultrasound examination when the fetus developed bradycardia.

●In another review of 328 pregnant patients with blunt abdominal trauma, ultrasound had lower sensitivity, detecting only 14 of 23 intraabdominal injuries [31]. Of note, sonographic evidence of injury consisted of isolated pelvic fluid in three cases.

Pediatrics — The use of ultrasound to evaluate the pediatric trauma patient is discussed separately. (See "Trauma management: Approach to the unstable child", section on 'e-FAST (extended focused assessment with sonography for trauma)'.)

CLINICAL STUDIES

Blunt abdominal trauma — The clinical use of ultrasound and the Focused Assessment with Sonography for Trauma (FAST) in the management of blunt abdominal trauma (BAT) is discussed above. Studies of the effectiveness of ultrasound in BAT are reviewed here. (See 'Focused Assessment with Sonography for Trauma' above and 'Abdominal examination' above.)

Numerous studies have been published investigating the role and effectiveness of ultrasound in the evaluation of BAT. Nevertheless, our ability to make comparisons and draw conclusions from this literature is limited because the majority of studies are retrospective and their methodologies vary widely [32].

The wide range of endpoints employed in studies of the FAST examination represents one example of their methodological limitations. Some studies include insignificant injuries identified by CT among their outcomes, which decreases the sensitivity of the FAST examination, while others use important clinical outcomes (eg, need for operative intervention), which improves the examination's test characteristics. Other endpoints have included the ability to detect free fluid or particular injuries, the need for additional tests and procedures, the time to surgery, cost, and mortality.

Determining appropriate outcomes in trauma studies can be difficult. Differences in mortality, while an important endpoint, are difficult to evaluate in severe trauma because of the high baseline mortality rate. To achieve adequate power, a prospective study attempting to determine the impact of ultrasound upon mortality would require a large number of severely injured patients.

The following studies illustrate the range of findings with respect to the effectiveness of FAST in BAT:

●A systematic review published in 2018 of observational studies of ultrasound in blunt abdominal and thoracic trauma (34 studies; 8635 patients) reported overall sensitivity to be 0.74 (95% CI 0.65 to 0.81) and specificity to be 0.96 (95% CI 0.94 to 0.98) [33]. The authors noted substantial heterogeneity among studies and reported that the accuracy of ultrasound varied by the location of injury and patient age (sensitivity and specificity were lower in children).

●A systematic review published in 2015 looking at randomized controlled trials (RCTs) of ultrasound-based algorithms for the management of blunt trauma concluded that the evidentiary basis supporting the use of such algorithms remains poor [5]. Heterogeneity among studies is great and methodologic quality limited.

●A systematic review published in 2012 of 22 prospective studies involving several thousand patients with blunt abdominal trauma described the FAST examination as the most accurate bedside test for evaluating intraabdominal injury [34]. According to this review, a positive FAST examination is significantly more accurate for detecting intraabdominal injury than any historical feature or examination finding (adjusted LR 30; 95% CI 20-46), while a negative FAST examination substantially decreases the likelihood of injury (adjusted LR 0.26; 95% CI 0.19-0.34). All studies included in the review used consecutive patient enrollment, a reference standard for diagnosis (eg, CT, laparotomy, autopsy), and blinding of ultrasonographers.

●The Sonography Outcomes Assessment Program (SOAP) study randomly assigned 262 patients with torso trauma to usual care or a protocol that included the FAST examination [35]. Use of FAST was associated with significant reductions in the following parameters: time to surgery by an average of 109 minutes (a 64 percent reduction, 95% CI 48-76 percent), CT use (odds ratio [OR] 0.16, 95% CI 0.07-0.32), hospital stay by 27 percent (95% CI 1-46 percent), complications (OR 0.16, 95% CI 0.07-0.32), and cost. This study highlights the important role of ultrasound as a triage tool to expedite definitive care.

●Significant benefit was also noted in a nonrandomized prospective study of 419 trauma patients who were or were not evaluated with a FAST examination [36]. Ultrasound led to a change in management in 33 percent of cases, resulting in lower rates of CT and diagnostic peritoneal lavage.

On the basis of the SOAP trial, multiple observational studies, and clinical experience, the majority of trauma centers use the FAST examination for the initial imaging of patients with blunt abdominal trauma. However, clinicians must keep in mind the limitations of ultrasound, most notably its variable sensitivity for intraabdominal injury. Further randomized controlled trials are needed to assess the impact of ultrasound upon clinically important outcomes [5,37]. (See 'Limitations of FAST' above.)

Penetrating abdominal trauma — The clinical use of ultrasound and the Focused Assessment with Sonography for Trauma (FAST) in the management of penetrating abdominal injury is discussed above. Performance of the sonographic examination in patients with penetrating abdominal trauma does not differ significantly from blunt trauma patients (see 'Focused Assessment with Sonography for Trauma' above and 'Abdominal examination' above). Studies of the effectiveness of ultrasound in penetrating abdominal trauma are reviewed here.

According to observational studies, a positive FAST examination in cases of penetrating abdominal trauma is highly specific and predictive of injury. However, the examination's sensitivity for penetrating injuries requiring surgery is significantly lower than that seen in blunt trauma.

No randomized trials have been performed to assess the impact of the FAST examination upon patient outcome, clinician decision-making, or resource use in the setting of penetrating abdominal trauma. In addition, no studies of ultrasound in hemodynamically unstable patients with penetrating abdominal trauma have been reported. A systematic review of eight observational studies of the FAST examination in penetrating trauma of the torso reported that specificity ranged from 94 to 100 percent while sensitivity might be as low as 28 percent [38].

The following studies illustrate the range of findings with respect to the effectiveness of FAST in penetrating abdominal trauma:

●A prospective observational study of 75 consecutive, hemodynamically stable patients with penetrating abdominal injury performed at a level one trauma center found the FAST examination to have a sensitivity of 46 percent and a specificity of 94 percent [39]. Of the 22 patients with false negative ultrasound studies, 13 had intraabdominal blood and sustained injuries requiring operative repair. Missed injuries included those to small and large bowel (n = 6) and the diaphragm (n = 3).

●A prospective observational study of 72 hemodynamically stable patients with penetrating torso trauma and no indication for emergent laparotomy or thoracotomy found the FAST examination to have a sensitivity of 67 percent and a specificity of 98 percent [40]. Of the 66 patients in the study who received a complete FAST examination, 53 had no discernible intraperitoneal fluid, but 6 of these 53 had significant intraabdominal injury detected by laparotomy or further imaging studies. Missed injuries included those to bowel (n = 3), diaphragm (n = 2), and stomach (n = 2).

●Another prospective observational study of 177 consecutive stable patients with penetrating injury to the abdomen or thorax found the FAST examination to have a sensitivity of 48 percent and a specificity of 98 percent [41]. Although the authors concluded that the FAST examination rarely altered management, the study did not report explicit, a priori criteria for management changes based upon ultrasound findings.

Blunt thoracic trauma — Injuries incurred from blunt thoracic trauma may involve the lungs, heart, and other mediastinal structures, and range from minor soft-tissue contusions to pneumothorax to cardiac or aortic rupture. The capacity of ultrasound to detect such injuries varies. The performance of the FAST examination is discussed above. Studies assessing the effectiveness of ultrasound in detecting injuries commonly sustained from blunt thoracic trauma are reviewed below. (See 'Focused Assessment with Sonography for Trauma' above and 'Pericardial and limited cardiac examination' above and 'Pleural examination' above.)

Pneumothorax and hemothorax — Multiple observational studies suggest that ultrasound may be an effective screening tool for the diagnosis of pneumothorax in patients with thoracic trauma [42-51]. Fewer studies have assessed the test characteristics of ultrasound for detecting clinically significant traumatic hemothoraces (eg, requires tube thoracostomy or emergency thoracotomy) but preliminary data are promising [52-56].

In a systematic review and meta-analysis of 13 prospective comparative studies, the overall sensitivity and specificity of ultrasound for pneumothorax were reported to be 91 (95% CI 85-94) and 99 percent (95% CI 97-100), respectively, while the overall sensitivity and specificity of supine plain chest radiography were 47 (95% CI 31-63) and 100 percent (95% CI 97-100), respectively [57]. Of the 13 studies included, nine (involving 1271 patients with 410 traumatic pneumothoraces) used patients as the unit of evaluation and were included in the primary analysis. Nevertheless, the test characteristics of ultrasound reported in the review should be interpreted cautiously. The authors found that all studies were at high or unclear risk of bias. In addition, many studies involved clinicians with advanced training in ultrasound or were performed in settings where ultrasound is widely used. Thus, both sensitivity and specificity may be overstated.

Cardiac and aortic injury — The clinical management of blunt cardiac injury is discussed separately. (See "Initial evaluation and management of blunt cardiac injury".)

In most patients, ultrasound readily detects clinically significant hemopericardium or massive hemothorax from blunt cardiac injury [49]. Ultrasonographic signs of cardiac injury may also include wall motion or valvular abnormalities. (See 'Pericardial and limited cardiac examination' above.)

When not immediately fatal, traumatic aortic injury (TAI) may present with partial thickness tears that progress to aortic rupture if not identified and repaired. Transthoracic ultrasonography, such as the examination performed as part of FAST, provides poor visualization of thoracic aorta. More sophisticated ultrasound techniques may allow visualization of the aortic root and portions of the ascending and descending aorta. Nevertheless, helical CT and transesophageal echo (TEE) are considered the standard means for evaluation of the aorta at risk of traumatic injury. (See "Initial evaluation and management of blunt thoracic trauma in adults", section on 'Aortic injury'.)

Rib and sternal injury — Fractures to the ribs and sternum are common with blunt thoracic trauma. Ultrasound is more sensitive for identifying rib fractures than chest radiograph, which has poor sensitivity [58]. Ultrasonographic findings of rib fractures include cortical offset and surrounding hematoma (image 15 and image 16).

Ultrasound is also effective for excluding potentially dangerous complications of rib fractures, such as pneumothorax (image 14 and image 7).

A meta-analysis of six studies with 663 patients compared chest ultrasonography with chest CT for identifying rib fractures [59]. Pooled sensitivity and specificity for ultrasound were good (89 percent, 95% CI 81-94 and 98 percent, 95% CI 90-100, respectively), and there was no difference between emergency clinician- and radiology-performed ultrasonography. Similar findings were reported in a separate prospective study examining both rib and sternal fractures [58].

Penetrating thoracic trauma — Penetrating thoracic trauma shares many characteristics with blunt thoracic trauma, including the risk of injury to the lungs, heart, and other mediastinal structures. Among the more common injuries in this setting are pneumothorax and cardiac tamponade. Performance of the Focused Assessment with Sonography for Trauma (FAST) is discussed above. Studies of the effectiveness of ultrasound in penetrating thoracic trauma are reviewed here. (See 'Focused Assessment with Sonography for Trauma' above and 'Pericardial and limited cardiac examination' above and 'Pleural examination' above.)

Overall, ultrasound appears to be an accurate test for the diagnosis of pneumothorax or hemopericardium in the setting of chest trauma and is widely used as an initial screening study in patients with precordial wounds [60-64]. Clinicians must take care not to confuse epicardial fat pads with true pericardial effusion [19].

There are reports of false-negative pericardial ultrasound examinations in the setting of trauma [61,65-67]. These inaccurate examinations occur most commonly in patients with concurrent, large hemothoraces or mediastinal hemorrhage. To improve accuracy in such cases, we recommend that the pericardial ultrasound examination be repeated after the hemothorax is cleared by chest tube. False-negative examinations remain possible despite such maneuvers if the hemopericardium empties into the thoracic cavity, thereby preventing blood from accumulating in the pericardium.

Few studies have assessed the effectiveness of ultrasound in the management of patients with penetrating thoracic trauma:

●A case series of 247 patients with penetrating thoracic trauma studied with bedside ultrasound identified 10 cases of hemopericardium, for which the mean time from ultrasound to operating room was 12.1 minutes [60]. This research group subsequently performed a prospective study of 261 similar patients and identified 29 cases of hemopericardium [61]. In this study the mean time to surgery was 12.1 minutes and the sensitivity and specificity of ultrasound for hemopericardium were 100 and 97 percent respectively.

●A retrospective review of 49 patients with penetrating cardiac injury found that the average time to diagnosis was shorter (15.5 versus 42.4 minutes) and survival was higher in the 28 patients who underwent a cardiac ultrasound examination by emergency clinicians immediately upon arrival in the emergency department compared to those managed without ultrasound [68].

●A prospective observational study of 32 patients with penetrating anterior chest wounds reported 100 percent sensitivity and specificity of ultrasound for hemopericardium [62].

Blunt and penetrating trauma

Ultrasound assessment of volume status — Focused transthoracic ultrasound evaluation of the heart and inferior vena cava (IVC) is being studied as a tool for improving the emergency triage and ongoing assessment of patients with major trauma of all types. While cardiac ultrasound appears to have excellent sensitivity for identifying hemopericardium, observational studies report that adding evaluations of the IVC and cardiac output, which are not currently performed as part of the standard FAST examination, may provide insight into the volume status and fluid responsiveness of severely injured trauma patients, and can easily be performed by emergency medicine physicians and trauma surgeons [69-74].

In a randomized trial performed at a single academic trauma center, 215 patients designated as high alert and manifesting at least one sign of hemodynamic instability were assigned to management that included a limited transthoracic echocardiogram (LTTE) or no LTTE [69]. Although the groups were similar in age and the severity and mechanism of injury, the LTTE group demonstrated statistically significant reductions in fluid administration (1.5 versus 2.5 L) and time required to move from the trauma bay to the operating room (35.6 versus 79.1 minutes), and a nonsignificant trend towards lower overall mortality (11 versus 19.5 percent), particularly among patients with traumatic brain injury (14.7 versus 39.5 percent). While promising, focused studies to assess volume status in trauma patients remain preliminary and further study is needed to determine the technique's effectiveness, and when and how it should be incorporated into the overall trauma evaluation.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: General issues of trauma management in adults".)

SUMMARY AND RECOMMENDATIONS

●Background – Ultrasound is portable, inexpensive, free of ionizing radiation, and allows the clinician to perform examinations rapidly and repeatedly to obtain diagnostic information at the bedside. Ultrasound provides accurate and useful information for the clinician performing the initial evaluation of the adult patient with trauma to the abdomen or chest. (See 'Overview' above.)

●Focused Assessment with Sonography for Trauma (FAST) – The FAST exam is the standard screening examination performed on trauma patients and involves assessments of the pericardium (to look for hemopericardium and tamponade) and of the right flank, left flank, and pelvis (to look for intraperitoneal free fluid).

In many cases, an extended evaluation looking for pneumothorax (E-FAST) is performed. The FAST and E-FAST examinations are most helpful when positive, in which case they decrease the time to definitive treatment.

●Elements of E-FAST – The fundamental assessments included in the E-FAST examination are the following:

•Pericardial and limited cardiac examination (see 'Pericardial and limited cardiac examination' above)

•Abdominal examination (see 'Abdominal examination' above)

•Pleural examination (see 'Pleural examination' above)

●Limitations of FAST – Limited sensitivity, especially in penetrating trauma, precludes the use of ultrasound as a definitive tool to rule out major intra-abdominal or intrathoracic injury. Ultrasound cannot discern diaphragmatic tears, pancreatic lesions, bowel perforation, mesenteric trauma, and small amounts of free fluid (generally <200 mL), which may suggest injury. Ultrasound's ability to detect injuries to the kidney is limited, and it cannot distinguish between urine and blood, which decreases its sensitivity and specificity in pelvic trauma. (See 'Limitations of FAST' above.)

●Improving FAST – Repeat examinations improve the sensitivity of ultrasound. (See 'Improving FAST' above.)

●Additional imaging – Hemodynamically stable patients with a concerning mechanism of injury or physical examination findings are evaluated with additional imaging studies (usually CT) or a period of observation including some combination of serial physical and ultrasound examinations. (See 'Overview' above.)

●Females of reproductive age – Ultrasound often identifies a trace amount of free pelvic fluid in female patients of reproductive age. Such fluid is associated with ovulation and generally considered physiologic. However, we believe it is best to assume that an injury exists when free fluid is found on the pelvic view in a female who has sustained significant abdominal or thoracic trauma. (See 'Females of reproductive age' above.)