Ultrasound for Trauma

Authors: Ashika Jain, MD, RDMS, Assistant Professor, Trauma Critical Care, Emergency Ultrasound, Director, Critical Care Ultrasound, Department of Emergency Medicine, Kings County Hospital Center, SUNY Downstate Medical Center, Brooklyn, NY.

Jay Menaker, MD, Associate Professor, Department of Surgery, Associate Professor, Department of Emergency Medicine, University of Maryland School of
Medicine, Baltimore; Physician Director of Quality Management, R Adams Cowley Shock Trauma Center, Baltimore, MD.

Peer Reviewer: Perry W. Stafford, MD, FACS, FAAP, FCCM, Professor of Surgery, UMDNJ Robert Wood Johnson Medical School, New Brunswick, NJ.

Traumatic injury remains one of the most important and persistent causes for morbidity and mortality in the United States. The establishment of a trauma team that is available to evaluate and manage trauma quickly and efficiently during the very critical first minutes after the injured patient arrives at the hospital has significantly improved survival and dramatically reduced sequelae from these injuries. An important component of this expedited evaluation has been the recognition of the utility of ultrasound to augment the imaging and triage of the injured patient. In this well-researched monograph, the authors describe this rapidly growing modality and its many applications. All members of the trauma team should be familiar with the indications and limitations of this important trauma tool.

— Ann M. Dietrich, MD, Editor

Introduction

Injury-related visits to the emergency department (ED) account for 34.2% of all visits.1 Rapid evaluation, management, and disposition are important steps in ED throughput. Bedside ultrasonography has rapidly changed the timeline to ultimate disposition, whether it is to the operating room, the floor, or home. The ability to confidently and noninvasively evaluate a trauma patient at the bedside has revolutionized the algorithm for initial examination, diagnostic evaluation, and management.

As ultrasound has gained importance in the initial evaluation of the trauma patient and made its presence at the bedside routine, the applications for utilization have expanded and now include line placement, vascular injury evaluation, fracture diagnosis, and expansion of the original Focused Assessment with Sonography for Trauma (FAST) exam to include the thorax.

As a bedside adjunct with immediate results, the ultrasound machine has become a vital tool for the evaluation of the trauma patient. A FAST exam can be performed during the primary survey, making the diagnosis of free fluid in the peritoneum, pericardium, or thorax instantaneous. In a patient with unstable vital signs, the information gained from the FAST exam can decrease time to definitive management and improve efficiency and time to the operating room.2-4 Furthermore, localizing the free fluid can help to direct the operative management. For example, lack of fluid in the abdomen with a fluid strip in the pericardium may assist with operative approaches. Not only is the time to the operating room decreased, but time to injury control/repair is decreased by early and efficient evaluation. Bedside ultrasound is noninvasive and reduces the need for diagnostic peritoneal lavage (DPL), and can be integrated into the primary and secondary survey as well as be repeated as needed. Additionally, it is safe in children and pregnant patients, as it has a significantly lower radiation profile than other imaging techniques.

History

Ultrasound found its place in science in the 1820s when Jean-Daniel Colladon, a Swiss physicist, successfully used an underwater bell to determine the speed of sound in the waters of Lake Geneva.5 However, it wasn’t until 1942 that doctor Karl Theodore Dussik of Austria published the first medical paper on ultrasonics describing his research on transmission ultrasound investigation of the brain. Since then, the utilization of ultrasound in medicine has grown tremendously. In Europe in the 1970s, ultrasound was recognized as a noninvasive, rapid, safe, accurate, and repeatable bedside assessment tool and was included in the trauma evaluation. Eventually, ultrasound made its way to America in the 1990s, displacing DPL as the initial diagnostic test in a trauma patient.6,7 The use of ultrasound for trauma has continued to expand and includes diagnosis and management of thoracic trauma and serves as a valuable adjunct for vascular access. This issue of Trauma Reports will review some of the old applications as well as many of the new applications for ultrasound.

Focused Assessment with Sonography for Trauma

The traditional FAST exam allows for a rapid evaluation of hemoperitoneum and hemopericardium. The test can be performed quickly at the patient’s bedside and does not require moving the patient from the resuscitation bay or emergency department. Additionally, it can be repeated rapidly and easily as needed, especially when vital signs change. The traditional FAST exam has four views: the subxiphoid view, looking at the pericardium; the right upper quadrant view, looking at Morison’s pouch and the right paracolic gutter; the left upper quadrant, looking at the splenorenal interface and the left paracolic gutter; and the suprapubic view, looking at the intraperitoneal pelvic space. (See Figures 1-5, normal FAST exam.)

Figure 1. Normal FAST Exam, Subxiphoid View

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Table 1. FAST Exam

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Figures 2-3. Normal FAST Exam, Right Upper Quadrant

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Figures 4-5. Normal FAST Exam, Left Upper Quadrant and Suprapubic View

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While at the bedside, the probe of choice is one that allows for evaluation of deep structures while maintaining optimum resolution. The large footprint, low-frequency curvilinear probe is the probe of choice. This probe gives the most information without compromising information gained for depth. Alternatively, the smaller footprint phased array probe can be used. This probe allows for access between the ribs while still allowing for evaluation of the deep structures.

A positive exam is one in which fluid is noted in any of the four views. Fluid appears dark and anechoic. The subxiphoid view is used to evaluate the pericardium. The presence of a dark, anechoic stripe between the myocardium and the pericardium represents pericardial fluid concerning for hemopericardium. It is important when visualizing the pericardium to make note of the posterior pericardium. Since this is the most dependent portion of the pericardium, this is where fluid initially settles. Most significant is the presence of fluid in the anterior pericardium, as this implies enough fluid has accumulated in the less dependent portion of the sac. A stripe of fluid between the liver and the kidney or the liver and the spleen represents fluid in the abdomen. The FAST exam is unable to specify which organ is injured, only identifying the presence of fluid, which indicates underlying pathology. The fourth view in the pelvis looks at the vesiculo-uterine space (pouch of Douglas) in females, and the rectovesicular space in males. A dark, anechoic, freeform stripe that does not configure to a wall either behind the bladder or behind the uterus (females) is indicative of injury. (See Figures 6-9, FAST exam with free fluid.)

Figures 6-7. FAST Exam with Free Fluid

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Figures 8-9. FAST Exam with Free Fluid

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Unfortunately, a negative FAST exam does not exclude an intra-abdominal injury. Reported sensitivity of ultrasound for detection of free intraperitoneal fluid varies, ranging from 62% to 99%, with negative predictive values of 89% to 99%.7-9 Combinations of clinical and ultrasound findings may be most useful to determine which patients do not require further evaluation.10,11 There has been some discussion about the usefulness of doing a FAST exam in the setting of a stable patient. In most trauma management algorithms, if a patient is stable and needs further imaging, a CT scan is most likely the test of choice; it gives specific information about the hollow viscus and solid organs, as well as the retroperitoneum, which the FAST exam is unable to evaluate. However, this requires the patient to be able to leave the emergency department and travel to the CT scanner and remain hemodynamically stable.

There have been many attempts to use contrast-enhanced sonography to better evaluate solid organ injury. Mihalik et al used contrast-enhanced sonography to confirm CT scan findings of solid organ injury. They were able to identify liver injuries with 62.5% sensitivity, splenic injuries with 100% sensitivity, and renal injuries with 50% sensitivity. The overall sensitivity was 79%, with a positive predictive value of 100% and negative predictive value of 20%.12 Contrast-enhanced sonography does not identify solid organ injuries with high enough sensitivity to replace CT scans in the complete evaluation of a patient with a blunt traumatic injury. It can be used to identify and follow splenic pseudoaneurysms, which may help to reduce radiation exposure in those patients who require serial evaluations.13-15 When this modality is used, the contrast is injected twice, once just prior to the left upper quadrant scan and then again just prior to the right upper quadrant scan. While injury to the parenchyma of the liver or spleen would appear hypoechoic, with the use of contrast-enhanced sonography, injury with vessel damage would appear as hyperechoic extravasation.13,15

The FAST exam has been shown to be most useful in unstable trauma patients.10,16,17 A FAST exam should be considered in hemodynamically unstable patients, especially when the cause of hypotension is unclear; in cases of penetrating trauma with multiple wounds or unclear trajectory; in patients with a concerning mechanism of injury but no indication for CT; and in intoxicated patients who can be observed and re-examined. (See Table 2.) Since transporting the patient to the CT scanner may not be an option, but a clear indication for operative management may not yet be evident, bedside ultrasound can be used for the initial evaluation and can be repeated for deteriorating or not improving vital signs.

Table 2. FAST Exam Considerations

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In the case of penetrating trauma, routine use of ultrasound is beneficial; the detection of pericardial or peritoneal fluid is clinically useful. However, the FAST exam is limited in that it cannot give information about the retroperitoneum, localize hollow and viscus injury, nor definitely identify solid organ injury. Therefore, a negative FAST examination does not exclude abdominal injury, such as a diaphragm or hollow viscus wound, and further diagnostic investigation or serial exams are indicated for any patient with a concerning exam.18

Localizing the compartment of injury can be used to direct operative management. For example, a gunshot wound in the thoraco-abdominal region could lead to an injury in the thorax, the abdomen, or both. The presence of fluid in Morison’s pouch may help the surgeon to direct the first incision and exploration in the abdomen.

EFAST

The added application of thorax evaluation to the FAST, dubbed the EFAST, has broadened the spectrum of bedside sonography. Using ultrasound to detect and diagnose pneumothorax at the bedside is more sensitive and specific than plain radiographs. The sensitivity of thoracic ultrasound was found to be 81.8% and the specificity was found to be 100%. The sensitivity of chest X-ray was found to be 31.8% and the specificity was found to be 100%.19 Garofalo et al found ultrasound sensitivity was 95.65%, specificity 100%, and diagnostic effectiveness 98.91%. Prompt and accurate diagnosis of a pneumothorax in the assessment of a critical patient can prevent the progression to a life-threatening situation.20 Recently, Husain et al have confirmed sonographic signs, including “lung sliding,” “B-lines” or “comet-tail artifacts,” “A-lines,” and the “lung point sign” can help in the diagnosis of a pneumothorax.21 “A lines” are parallel horizontal lines representing an artifact of the pleura. (See Figure 10.) The presence of these lines implies normal lung. “B lines” are a comet-tail artifact of vertical lines representing the interface between aerated and compressed lung. The lung point is the interface between a pneumothorax and the lung. Using these sonographic findings can help to quickly direct care.

Figure 10. A Lines Indicating Normal Lung Function (left image)
Figure 11. Stratosphere Sign (right image)

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Chest ultrasound views consist of four locations of each hemithorax, an eight-point exam in total. The four views are: anterior second intercostal space at the midclavicular line; fourth intercostal space at the anterior axillary line; sixth intercostal space at the midaxillary line; and sixth intercostal space at the posterior axillary line. (See Table 3.) The linear high-frequency probe allows for evaluation of superficial structures and is therefore the probe of choice to assess for the presence of a sliding lung sign to exclude pneumothorax. In the normal lung, the parietal and visceral surfaces can be visualized by ultrasound as bright interfaces or echogenic lines. With respiration, these two bright lines slide past each other. This phenomenon has been described as ants marching on a log or, simply, the pleural sliding sign. This sliding is seen on ultrasound deep to the ribs. If air, as in the case of a pneumothorax, were to seep in between the parietal and visceral pleura, the deeper pleural layer would not be visualized due to the inability of medical ultrasound to penetrate through air. Thus, since half of the sliding component is invisible, no sliding lung sign is seen. The edge of the collection of air where it meets the lung is the lung point. Air usually rises and can be found in the least dependent aspect of the chest cavity; therefore, the exam should start in this area. However, if a patient has had any sort of lung process previously, the possibility of adhesions may cause air to be trapped in an area other than the zenith of the chest space. Therefore, the protocol includes looking around the chest space.22,23 Once the pleura have been identified, the ultrasound should be done in B mode as well as M mode. M mode displays a B mode image and plots it over time. In the pneumothorax study, it allows evaluation of pleural movement over time. In the normal lung, it would appear as sand on the beach with waves in the distance, or the sea shore sign. The sand represents an artifact caused by ultrasound waves hitting the air in the normal lung, which is constantly moving with each breath. If a pneumothorax is present, this appears as a bar code in M mode. The stratosphere sign is seen in M mode, with pleura and lung indistinguishable as linear hyperechogenic lines, and is a reliable sign of pneumothorax. (See Figure 11.) Ultrasound can also be used to confirm adequate decompression. In one study, ultrasound was used to confirm decompression after needle thoracostomy for tension pneumothorax.24

Table 3. Chest Ultrasound Views

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To evaluate for effusion, the curvilinear probe can be used while it is in the right and left upper abdominal quadrants. The presence of the spinal stripe above the diaphragm is indicative of an effusion; in the traumatic setting, this can be assumed to be blood. The spine appears as a scalloped line that usually stops at the diaphragm. Air prevents ultrasound waves from penetrating deep enough to see such images in the thorax; with the presence of fluid, posterior elements such as the spine can be seen.25,26 (See Figures 12-13.)

Figures 12-13. Pleural Effusion

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Vascular Access

Ultrasound has long been used as an adjunct for central line placement; additionally, it has been shown to reduce time and number of attempts for peripheral line placement.27 Often, traumatic patients present in shock, making peripheral line placement difficult due to peripheral venous collapse. Patient co-morbidities, such as obesity, drug use, or other medical conditions, may further complicate venous access. Ultrasound has been shown to decrease time to cannulation, as well as the need for central line access due to difficult peripheral access.28,29 Shokoohi and colleagues describe an 80% decrease in the need for central line access due to successful peripheral line placement with ultrasound.

A liner probe is used, similar to central line placement, with transverse and longitudinal views utilized to optimize visualization. Use of ultrasound gel has not been shown to increase infection rates compared to traditionally placed lines.29-32

Bladder Injury

Ultrasound has been used to evaluate for specific intra-abdominal injuries as well. Wu et al describe a case report of diagnosing bladder rupture via bedside ultrasound. While the most extraperitoneal bladder is usually protected by the bony pelvis, the superior portion of the bladder is intraperitoneal. When distended, the dome of the bladder is unprotected from blunt force, leading to intraperitoneal bladder rupture. Wu et al describe a patient with no evidence of urethral injury and Foley placement with hematuria. The FAST exam showed free fluid in the suprapubic view with an irregular, collapsed bladder. A CT scan confirmed the diagnosis. Isolated bladder injury has up to a 22% mortality, making prompt diagnosis and repair paramount.33,34

Pneumopericardium

Bobbia and colleagues describe the diagnosis of pneumopericardium via bedside echocardiography in a patient with respiratory distress. Bright spots were seen rapidly moving along the pericardial layer during diastole, with comet-tail artifacts extending across the whole image of the heart and disappearing during systole, suggesting pneumopericardium. This is a similar artifact that is sought when evaluating the lungs for normal movement vs. pneumothorax.35

Femoral Nerve Block

Haines et al describe using ultrasound for hip fractures. Patients with hip fractures are often treated with intravenous opiates, which may cause many adverse effects, particularly in elderly patients. An alternative to systemic opioid analgesia is a nerve blockade. In a study by Haines et al, an ultrasound-guided fascia iliaca compartment block was performed in any patient presenting to the emergency department with a confirmed hip fracture. Patients were randomized to receive either intravenous analgesics or a nerve block. Pain scores were evaluated up to 8 hours, with an overall reduced pain severity score at 120 minutes.36 (See Figures 14-15, courtesy of Haines.)

Figures 14-15. Femoral Nerve Block

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Special Populations

Resuscitation in Pregnancy. Traditional practices for evaluation of the third trimester pregnant hypotensive patient routinely utilize the left lateral decubitus position. This theoretically relieves the pressure of the uterus on the inferior vena cava (IVC), thereby improving venous return. Fields and colleagues found that while 76% of patients showed an increase in IVC size with left lateral decubitus positioning, the remaining patients showed the largest IVC measurement in the supine position. Utilization of ultrasound to evaluate the IVC during resuscitation may help to appropriately manage positioning for this special patient population.37

Fractures. Rib fractures can also be diagnosed using ultrasound, and ultrasound has been shown to be more sensitive than radiographs, especially for fractures in the costal margin or along the costal cartilage. Fractures of the rib, costochondral junction, and costal cartilage appear as a disruption of the anterior echogenic margin of the rib. The costal cartilage normally appears relatively hypoechoic compared with the osseous rib.38 This is an especially useful tool in children and pregnant women in whom minimizing radiation exposure is an important consideration. Using a linear probe, a fracture would be seen as a disruption of the bony contour as the rib is followed outward.

In addition, ultrasound has been used to diagnose many types of fractures, including the clavicle and elbow, as well as the distal forearm. Ultrasound is particularly useful in the pediatric population, in whom reduction in radiation is an important consideration. Furthermore, bedside evaluation helps to keep these patients calm and reduce the anxiety associated with being moved from the emergency department.39-41

Ocular Ultrasound

Emergency bedside ultrasound is highly accurate for excluding and diagnosing ocular pathology. Further, it accurately differentiates between pathology that needs immediate ophthalmologic consultation and that which can be followed up on an outpatient basis.42 It can be used to evaluated for diagnosis of retinal detachment, foreign body detection, and increased intracranial pressure, as well as to look for pupillary response in the patient with significant periorbital edema/hematoma in which the eyelids cannot be opened.

Ocular ultrasound is performed using a high-frequency linear probe at its lowest setting. On some machines there is an ocular preset that should be used in conjunction with a closed eye technique. Using a clear dressing to cover the closed eye, copious standard water-soluble gel should be applied to prevent direct contact between the probe and the globe. The normal eye appears as a circular hypoechoic structure. The anterior chamber is filled with anechoic fluid and is bordered by the cornea, iris, and anterior reflection of the lens capsule. The iris and ciliary body are seen as echogenic linear structures extending from the peripheral globe toward the lens. The normal lens is anechoic. The normal vitreous chamber is filled with anechoic fluid. The vitreous is relatively echolucent in a young healthy eye.

Retinal detachment is a true medical emergency. It often is a time-critical, vision-threatening condition. Evaluation for retinal detachments in patients with acute visual change is of particular importance, as immediate identification and treatment of this condition is imperative to prevent deterioration to permanent, complete visual loss. Without treatment, all cases of retinal detachment will spread and involve the macula, causing blindness.43 Vitreous detachment and hemorrhage can often mimic retinal detachment.44 A retinal detachment appears as a taut linear opacity within the vitreous chamber that moves in conjunction with eye movements. Vitreous hemorrhage consists of wavy linear or curved strands connecting with the retina that sway as the eye moves from side to side. A vitreous detachment occurs when the vitreous humor detaches from the posterior retina, which results in a mobile “swaying seaweed” appearance on ultrasound, where the vitreous appears separated from the retina.44 (See Figures 16 and 17.)

Figure 16. Normal Eye

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Figure 17. Retinal Detachment

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Ocular trauma is fairly common and should be suspected in patients involved in trauma with airborne material. Ritchie et al found that ultrasound was as sensitive as CT scan in detecting blast injuries.45 Foreign bodies in the globe can be devastating and require immediate attention. Often this is a subtle finding during the secondary survey, and commonly it is difficult to evaluate given that it is commonly accompanied by periorbital edema. Systematic imaging assessment should include the position, the contour, and volume of the globe, the density within the globe, the contours of the retina and sclera, and the presence of foreign bodies.46 Ultrasound is contraindicated if globe rupture is suspected, as the slightest amount of pressure can cause expulsion of vitreous. (See Figure 18.)

Figure 18. Globe Rupture

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Eliciting pupillary responses can be rendered impossible when the eyelid is swollen shut. In these instances, ocular ultrasound to look for consensual response to light can be employed.47 With light shining in the non-edematous eye, the iris should contract, with movement visible on ultrasound. One limitation to this exam is the inability to measure pupil size.

Ocular ultrasound for increased intracranial pressure has been described extensively. While there is a high normal variant rate, in the correct clinical setting, measurement of the optic nerve sheath diameter using bedside ultrasound has been shown to correlate with clinical and radiologic signs and symptoms of increased intracranial pressure.48-50 The diameter is measured 3 mm behind the globe using a high-frequency linear probe. Optic nerve sheath diameter measurement correlates with invasive measurements with a sensitivity of 94% and specificity of 76%, thus confirming its usability.49,51 (See Figure 19.)

Figure 19. Optic Nerve Sheath Diameter Measurement

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Foreign Body

Penetrating injury with a retained foreign body is a common problem. Locating the foreign body and performing surgical excision may be difficult for many reasons. It is further complicated when the object is not radio-opaque and is embedded in the deep tissue. Although radiographs have been proven to be ineffective, X-ray is often the first method used. Ultrasound can be a sensitive tool in both the detection and surgical removal of retained foreign bodies in soft tissue.52,53 Furthermore, ultrasound can be used in real time to guide extraction. (See Figure 20.)

Figure 20. Foreign Body with Reverberation Artifact

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Conclusion

Bedside ultrasound applications are growing rapidly. The information provided leads to early diagnosis and disposition. The FAST exam has expanded to include the thorax as an integral aspect of the exam. Furthermore, ultrasound has earned its position at the bedside not only for diagnosis but as an adjunct for procedures. Proficiency in bedside ultrasound evaluation is of utmost importance as its utility continues to grow.

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