Focused Assessment with Sonography for Trauma

Key points

  • Focused assessment with sonography for trauma (FAST) is a technique used for identifying fluid in the abdomen, pelvis, or pericardium. It involves 4 cardinal views: right (hepatic/renal), left (splenic/renal), cardiac (subxiphoid or transthoracic), and pelvic (bladder/rectal or uterine).

  • E-FAST is a modification that adds a transthoracic segmental view of the chest to identify intrathoracic air. It can also be used to identify pulmonary edema in the critically ill patient.

  • Indications for performing FAST and E-FAST include but are not limited to: acute traumatic shock, abdomen that cannot be examined, concern for intra-abdominal fluid, pneumothorax, and as triage tool in a mass casualty situation.

  • A positive FAST finding in a patient in shock or a victim of trauma should be assumed to be blood until proven otherwise.

  • The learning curve for performing FAST is fairly steep and therefore should include a mentoring period.

  • False-negative FAST examinations can occur due to operator inexperience or equipment variability. Additionally, false-negative findings can be found in patients with previous surgery, obesity, or pelvic fractures and with interval or early bleeding. Therefore a negative FAST in a patient who continues to be unstable should not prevent exploration or another diagnostic test such as repeat FAST, computed tomography scanning, or peritoneal tap.

Introduction

Patients presenting to the emergency department after major trauma may have multiple reasons for shock or present with an unreliable physical examination. One of the primary roles of the advanced trauma life support (ATLS) survey is to uncover immediate and potential life threats including hemorrhage and pneumothoraces. Because hemorrhage into the abdomen or pelvis cannot be conclusively confirmed on physical examination, an additional test is often necessary. The FAST (focused assessment with sonography for trauma) and its modification, E-FAST (extended FAST), are diagnostic techniques that allow for the rapid identification of fluid in the abdomen/pelvis or air in the thorax. This is particularly useful in patients presenting in shock with an unknown etiology and in patients with unreliable physical examinations.

The FAST examination is designed for 1 purpose, that is to identify fluid within the abdomen/pelvis or pericardial sac. It relies on understanding how fluid pools in the body in response to gravity. The abdomen and pelvis are shaped like a set of buckets suspended on a curved handle ( Figs. 1 and 2 ). This symmetry is the same whether one looks from right to left or cranial to caudal and results in fluid pooling in the posterior upper abdomen, pelvis, and right and left pericolic gutters. Ultrasound waves will pass through fluid and therefore appear black on the resulting image ( Fig. 3 ) The FAST examination uses the natural sonographic contrast between solid organs and fluid combined with the physics of fluid flow in the human peritoneal cavity to identify likely areas of fluid accumulation. The 4 classic FAST viewing angles take advantage of these anatomic constants. The 4 classic FAST views visualize these boundaries and include

  • Right flank: liver and kidney

  • Left flank: spleen and kidney

  • Pelvis: rectum/uterus and bladder

  • Cardiac: heart and chest wall

Fig. 1
Transverse view of abdomen. This CT scan illustrates the dependent portions of the abdominal cavity ( red arcs ) in the transverse plane.

Fig. 2
Sagittal view of abdomen. This CT scan illustrates the dependent portions of the abdominal cavity ( red arcs ) in the sagittal plane.

Fig. 3
Fluid in the dependent areas. This combination view shows how fluid will be outlined in the dependent areas that are visualized with the FAST examination.

E-FAST looks, not for fluid, but air. Air does not transmit ultrasound waves or reflect them. Therefore, in this situation, one must look for the artifacts created by separating 2 surfaces normal in opposition. In the case of the thorax, these surfaces are the visceral and parietal pleura. When these surfaces slide against each, other they cause interference in the ultrasound waves, resulting in a scattering effect often referred to as a comet tail ( Fig. 4 ). When air is present, these normal artifacts disappear, because the visceral and parietal pleura are no longer in opposition to each other ( Fig. 5 ).

Fig. 4
Thoracic view E-FAST normal. This ultrasound image illustrates the comet tails seen on a normal thoracic view.

Fig. 5
Thoracic view E-FAST abnormal. This ultrasound image illustrates the absence of the comet tails, indicating a pneumothorax.

Introduction

Patients presenting to the emergency department after major trauma may have multiple reasons for shock or present with an unreliable physical examination. One of the primary roles of the advanced trauma life support (ATLS) survey is to uncover immediate and potential life threats including hemorrhage and pneumothoraces. Because hemorrhage into the abdomen or pelvis cannot be conclusively confirmed on physical examination, an additional test is often necessary. The FAST (focused assessment with sonography for trauma) and its modification, E-FAST (extended FAST), are diagnostic techniques that allow for the rapid identification of fluid in the abdomen/pelvis or air in the thorax. This is particularly useful in patients presenting in shock with an unknown etiology and in patients with unreliable physical examinations.

The FAST examination is designed for 1 purpose, that is to identify fluid within the abdomen/pelvis or pericardial sac. It relies on understanding how fluid pools in the body in response to gravity. The abdomen and pelvis are shaped like a set of buckets suspended on a curved handle ( Figs. 1 and 2 ). This symmetry is the same whether one looks from right to left or cranial to caudal and results in fluid pooling in the posterior upper abdomen, pelvis, and right and left pericolic gutters. Ultrasound waves will pass through fluid and therefore appear black on the resulting image ( Fig. 3 ) The FAST examination uses the natural sonographic contrast between solid organs and fluid combined with the physics of fluid flow in the human peritoneal cavity to identify likely areas of fluid accumulation. The 4 classic FAST viewing angles take advantage of these anatomic constants. The 4 classic FAST views visualize these boundaries and include

  • Right flank: liver and kidney

  • Left flank: spleen and kidney

  • Pelvis: rectum/uterus and bladder

  • Cardiac: heart and chest wall

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Focused Assessment with Sonography for Trauma
Premium Wordpress Themes by UFO Themes