Authors: Bob Stuntz, MD, RDMS and Tom Kehrl, MD, RDMS
Focused Assessment with Sonography in Trauma (FAST) is a bedside tool that utilizes ultrasound (US) to help with the evaluation of the acutely traumatized patient. It has its roots in Europe, first utilized by German surgeons to help with care of unstable trauma patients (1). Trauma surgeons started using the FAST exam in United States trauma bays in the 1990’s and its use has continued to spread. The FAST exam is used as a rapid screening tool in the primary evaluation of trauma patients for the presence of hemoperitoneum and hemopericardium and its use has largely replaced diagnostic peritoneal lavage (DPL). However, the utility of the FAST exam in the hemodynamically stable patient is still being debated. So where do we stand and where do we go from here?
In order to answer this question and apply the exam in the correct clinical setting, it is important to know the limitations of the FAST exam. First, the FAST exam performs poorly in evaluating for visceral organ injury, retroperitoneal hemorrhage and rarely is able to determine the location of solid organ injury. Therefore, a negative FAST exam does not eliminate the need for further evaluation in patients in whom such injuries are suspected. Ultrasound is operator-dependent and both sensitivity and specificity suffer in the hands of the novice sonographer. Body habitus also has implications, as larger patients are more difficult to evaluate. Depth of tissue penetration by US waves is limited; with increasing depth and decreasing frequencies required for deeper penetration, resolution is poor. Another concern in the trauma setting is the presence of free intraperitoneal or subcutaneous air. US waves travel poorly through air and the presence of air between the probe and the target organ can render images uninterpretable (2).
The major indication for performing the FAST exam is in the unstable trauma patient to evaluate for the presence of intraperitoneal and/ or pericardial free fluid, thus guiding further work up and therapy. The utility of this is intuitive - having the ability to rapidly evaluate the peritoneum and pericardium for the source of instability without the patient leaving the clinician’s care can garner a significant advantage. However, the overwhelming theme in the literature involving the FAST exam is that the specificity is high but sensitivity is quite low. A recently published retrospective review article in Surgery showed an overall sensitivity of 43%, specificity of 99%, and an accuracy of 94.1% (3). A 2003 study by Miller et al. published in the Journal of Trauma compared the results of FAST exam and CT in 359 patients with suspected blunt abdominal injury. The FAST exam was found to have a of sensitivity 42%, and as suspected, missed blunt abdominal injury that was found on CT (4).
The recent literature on the role of the FAST exam in the evaluation of the stable blunt trauma patient is mixed. A prospective study comparing blunt trauma patients who were randomized to a FAST inclusive versus exclusive evaluation protocol focused on patient outcomes (5). Patients with torso trauma who presented to one of two urban Level 1 trauma centers and did not require immediate operative interventions were included. Characteristics of the two groups were similar. Patients who underwent FAST exam were shown to have faster disposition to the operating room, underwent fewer CT scans, and had shorter hospitalizations with fewer overall charges than those whose initial evaluation did not include evaluation with a FAST examination. Moylan et al. performed a retrospective cohort analysis of 1,636 normotensive blunt trauma patients that showed a strong association between a positive FAST exam and the need for therapeutic laparotomy. 37% of patients with a positive FAST exam needed therapeutic laparotomy, compared to 0.5% of patients with a negative FAST exam (6).
An advancement in the standard FAST examination, the eFAST (extended Focused Assessment with Sonography in Trauma), may help with the evaluation of the stable trauma patient. The FAST exam consists of four standard windows: the perihepatic (Morison’s pouch), pelvic, and perisplenic views are all used to evaluate for intraperitoneal blood and the subxyphoid window is used to evaluate for pericardial blood. The eFAST includes the evaluation of the thorax. Moving the probe in a cephalad direction in the perihepatic and perisplenic views allows for evaluation of hemothorax. Views of the anterior thorax allow the sonologist to evaluate for pneumothorax.
Evaluation for pneumothorax / hemothorax is one area in which US has been shown to be superior to the standard evaluation of the trauma patient. Upright chest radiography has a sensitivity of 92% for the evaluation of pneumothorax (7). Most trauma patients arrive in the trauma bay or emergency department supine on a backboard with cervical spine precautions in place, thus precluding the upright chest X-ray and necessitating a supine chest XR. This is problematic, as supine chest X-ray has a sensitivity of 50% for the detection of pneumothorax (7). Lung sliding is the sonographic visualization of the parietal and visceral pleural moving against each other during normal respiration. A lack of lung sliding on thoracic US (sonographic evidence of loss of apposition of the parietal and visceral pleura) has a sensitivity of 92-98.1% and a specificity of 99.7-100% for detection of pneumothorax. Visualization of a lung point (a point where normal lung sliding is juxtaposed with an absence of lung sliding) has a specificity of 100% (8, 9, 10). It is important to keep in mind that false positives can occur in apneic patients, mainstem intubation, pulmonary contusion, and those with significant pleural adhesions or scarring.
The FAST exam has limitations and there is contradictory evidence on the role of the FAST exam in the hemodynamically stable trauma patient. However, it is inexpensive, safe when performed at the proper time during a trauma resuscitation, repeatable, does not subject the patient to additional ionizing radiation, and can provide valuable information about a variety of clinically important traumatic injuries in a very short period of time. Its use should predominantly be as a screening tool and a negative test result should prompt further investigation, as evidenced by its low sensitivity. As well, hemodynamic stability can change quickly and knowledge of the presence of pneumothorax, hemothorax, hemopericardium, or hemoperitoneum early in the management of trauma patients can be very beneficial. Having the ability to properly perform and interpret this exam on the appropriate patient at the proper time and understanding its indications and limitations is crucial for any practitioner involved in the care of trauma patients.
- Hoffmann R, Pohlemann T, Wippermann B, et al. Management of sonography in blunt abdominal trauma. Unfallchirurg. 1989; 92:471-476.
- Jehle D, Heller MB. Ultrasonography in Trauma: The FAST Exam. The American College of Emergency Physicians. August 2003.
- Natarajan B, Gupta PK, Cemaj S et al. FAST scan: Is it worth doing in hemodynamically stable blunt trauma patients? Surgery. 2010 Oct; 148(4):695-700.
- Miller MT, Pasquale MD, Bromberg WJ et. al. Not so FAST. Journal of Trauma. 2003 Jan; 54(1):52-9
- Melniker LA, Leibner E, McKenney MG, et al. Randomized controlled clinical trial of point-of-care, limited ultrasonography for trauma in the emergency department: The first sonography outcomes assessment program trial. Ann Emerg Med. 2006; 48:227-235.
- Moylan M, Newgart C, Ma J et al. Association between a positive ED FAST examination and therapeutic laparotomy in normotensive blunt trauma patients. J Emergency Med. 2007; 33(3): 265-271.
- Omar HR, Abdelmalak H, Mangar D et al. Occult pneumothorax, revisited. Journal of Trauma Management & Outcomes 2010, 4:12.
- Blaivas M, Lyon M, Duggal S. A Prospective Comparison of Supine Chest Radiography and Bedside Ultrasound for the Diagnosis of Traumatic Pneumothorax. Academic Emergency Medicine 2005; 12(9): 844-850.
- Knudtson JL, Dort JM, Helmer SD, & Smith RS. Surgeon-performed ultrasound for pneumothorax in the trauma suite. J Trauma 2004 2004;56:527-530.
- Dulchavsky SA, Schwarz KL, Kirkpatrick AW et al. Prospective evaluation of thoracic ultrasound in the detection of pneumothorax. J Trauma 2001. 50; 201-205.