The Use of Ultrasound in Abdominal Trauma Patients
Published: Friday, January 7, 2005 at 2:18 p.m.
Last Modified: Friday, January 7, 2005 at 2:18 p.m.
Ultrasound has found its way into emergency medicine over the past ten years. It is now part of the formal training process of emergency medicine residents. Emergency medicine has found ultrasound very useful for the evaluation of not only abdominal trauma, but also for other emergent medical conditions including evaluations for renal colic, gallbladder disease, abdominal aortic aneurysm, line placements, as well as to rule out ectopic pregnancy. These emergent medical conditions can be rapidly diagnosed at the bedside with a trained emergency medicine physician.
Ultrasound and evaluation of abdominal trauma has continually changed over the past 30 years. Initially described by Kristensen and colleagues in 1971, Ascher and colleagues (Radiology - 1976) first reported the accuracy of ultrasound, with an 80% sensitivity for the detection of splenic injury. In 1990, Tiling and colleagues examined a group of 808 patients and reported a sensitivity of 89%, a specificity of 100%, and an accuracy of 98% for splenic injury in traumatized patients. This same group also commented on the importance of effective training and experience, reporting that surgeons with ultrasound experience could diagnose intra-abdominal fluid with a sensitivity of 98% and an accuracy of 99%. In the Gulf War, the military first made use of portable ultrasound machines as part of the field triage mechanism for traumatized soldiers in the field.
During this same time, ultrasound technology was improving with more inexpensive machines, much more portability, and improved picture quality. Emergency medicine physicians and surgeons began to publish their experiences with ultrasound in the assessment of trauma patients. In 1976, Rozycki et al developed the term Focused Assessment with Sonography for Trauma (FAST). This is a basic four-view of the abdomen and includes the perihepatic, perisplenic, pelvic, and pericardial views. These four exams form the basis of the FAST examination. This is a rapid non-invasive study performed at the bedside to rapidly evaluate critically injured patients for the presence of intra-abdominal bleeding.
The purpose of this article is to outline the general techniques involved in the performance of the FAST exam by emergency medicine physicians as part of the evaluation for abdominal trauma.
Ultrasound in Trauma
Ultrasound technology has become increasingly useful to ED physicians in a variety of situations, especially in the evaluation of the traumatically injured patient. While it does not replace other diagnostic tests like computed tomography or angiography in defining injuries, it can offer valuable information for risk-stratifying patients with blunt abdominal trauma.
The FAST exam stands for Focused Assessment with Sonography in Trauma. It can be performed with any basic 2-D ultrasound machine using an abdominal or cardiac probe. No Doppler technology is needed. FAST consists of four to six views of the abdomen and chest. During the evaluation, the FAST should be performed after the primary survey is completed.
Beginning in the right upper quadrant (RUQ), the first view examines Morrison's pouch. Hold the probe with the indicator toward the patient's head and place the probe on the mid to anterior axillary line between ribs 10 and 12. The target image is the line interface between the upper pole of the right kidney and the inferior border of the liver. There should be nothing visible between the two organs. This area is the most dependent portion of the peritoneal cavity when a patient is lying supine, therefore this is the first place peritoneal free fluid will accumulate regardless of the source of bleeding. When free fluid is present, it appears as a dark stripe separating the kidney from the liver.
Once Morrison's pouch has been examined, additional information about chest injury can be obtained by sliding the probe superiorly along the ribcage in the mid-axillary line until the diaphragm is visible as a bright line above the liver. The diaphragm will rise and fall several centimeters with respiration. A hemothorax appears as a dark stripe above the bright line. As the hemothorax enlarges, the lung may be seen floating in the dark fluid.
The second view examines the heart for cardiac activity and fluid in the pericardial space. Hold the probe with the indicator to the patient's right side and place the probe in the subxiphoid area and angle it toward the patient's heart with a scooping motion under the lower left ribs. Because the ultrasound beams must pass through a portion of the abdomen before contacting the heart, the ultrasound depth should be set to 17-20 cm. The heart will have a bright line of pericardium surrounding it. A pericardial effusion will appear as a dark stripe of fluid around the heart inside this bright outline.
The third view examines the left upper quadrant at the splenorenal recess. It has a similar sonographic appearance as the RUQ view. Hold the probe with the indicator toward the patient's head and place the probe on the posterior axillary line between ribs 8 and 10. The target image is the line interface between the spleen and the upper pole of the left kidney. Free fluid will again appear as a dark stripe separating the organs. Locating this view may be more difficult than the RUQ view because the spleen is smaller in size than the liver and the left kidney is more superiorly located than the right. The left chest can be examined for hemothorax in the same manner as the right, by sliding the probe superiorly along the ribcage in the mid-axillary line until the area just above the diaphragm can be seen.
The final view examines the interior portion of the peritoneal cavity. Hold the probe with the indicator towards the patient's right and place the probe immediately superior to the pubic symphysis. The target image is the bladder and the area posterior to it, the pouch of Douglas. When the probe is held horizontal to the body, with the indicator to the patient's right, the bladder appears as a dark circle or square, depending on the bladder volume. The area behind the bladder should appear bright, but when free fluid is present, it will appear as dark areas with bowel loops floating in it. Depending on the interval between the patient's injury and evaluation, free fluid may not have had time to accumulate to volumes that can be seen with ultrasound, usually 200-500 cc, so the complete FAST or the RUQ view alone may be repeated to assess for delayed accumulation of fluid or increased fluid accumulation.
Ultrasound is very sensitive in detecting the presence of free fluid in the peritoneal cavity, but is less sensitive in defining injury to solid organs. Most free fluid will accumulate first in the RUQ then spill down the right paracolic gutter to the pouch of Douglas, but the presence of fluid cannot predict which organ is injured. Ultrasound cannot fully assess the retroperitoneal spaces, which may be an area of significant bleeding seen only with CT scan. Finally, ultrasound is technically difficult in the severely obese population.
Once the FAST is completed, the presence or absence of fluid should be interpreted with the patient's hemodynamic status and any complaints of abdominal pain. Patients generally fall into one of four groups:
1. Patients who have no abdominal pain or tenderness, no hypotension, and no free fluid on FAST exam will usually not require any additional abdominal imaging. Serial FAST exams may be performed if the patient is to be admitted or observed for other injuries.
2. Patients who are hypotensive with free fluid on FAST exam should undergo emergent laparotomy to locate and control the source of bleeding.
3. Patients who have free fluid on FAST exam but are hemodynamically stable can have a CT abdomen to better define their abdominal injury, but they should be closely monitored. Patients with persistent complaints of abdominal pain and tenderness, or patients with inadequate FAST exams should also undergo CT imaging.
4. The final group of patients includes those with hypotension but no free fluid on FAST exam. These patients may have long bone injuries or retroperitoneal hemorrhage causing their hypotension. Many authorities recommend performing a diagnostic peritoneal lavage in this group to completely rule out intraperitoneal bleeding before addressing other injuries.
Patients with hypotension and significant pericardial fluid collection will require emergent pericardiocentesis, and ultrasound can be used to locate and guide catheter placement. Examining the area above both diaphragms can improve interpretation of a supine chest x-ray by locating the presence of a hemothorax.
Ultrasound examination of the traumatically injured patient is becoming part of the standard trauma resuscitation. With practice, these four images of the abdomen and chest can be obtained in 2-3 minutes and can easily be repeated as the patient's condition changes. While ultrasound has a limited ability to define solid organ injury and retroperitoneal injury, it is most useful in identifying those patients who require emergent laparotomy or pericardiocentesis, therefore decreasing delays in care.
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