The extended fast protocol

Published on 22/03/2015 by admin

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Last modified 22/03/2015

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The extended fast protocol

YEKATERINA GREWAL, ARIEL L. SHILOH and LEWIS A. EISEN

Overview

Ultrasound has become a permanent part of the evaluation of trauma patients ever since its first use in the emergency department more than 30 years ago.¹ First used in Europe in the 1970s, abdominal ultrasound ultimately replaced diagnostic peritoneal lavage during the 1980s.² Currently, bedside ultrasound is the initial imaging modality of choice for trauma care and is integrated into the Advanced Trauma Life Support protocol developed by the American College of Surgeons.³

“FAST,” an acronym for the focused assessment with sonography in trauma, was first described by Rozycki and Shackford ⁴ in 1996. The basic four-view examination consisting of perihepatic, perisplenic, pelvic, and pericardial views has become the foundation of FAST. The ability to be performed rapidly and safely during resuscitative measures makes it an ideal initial imaging modality in trauma patients. Ultrasound is reliably sensitive in diagnosing free fluid and free air in peritoneum, allowing the rapid recognition of hemoperitoneum and perforated viscera in hypotensive patients and traumatic injuries.^5–8 Previous work demonstrated that ultrasound has a higher sensitivity (49%-99%) than standard chest radiography (27%-75%) in the identification of hemothorax or pneumothorax.^9–12 The extended FAST (e-FAST) protocol, which includes the assessment of the lung and pleura bilaterally and the subcostal cardiac view, has been developed as point-of-care ultrasound for assessing and treating thoracic pathology in the intensive care environment. Its use has increased considerably over the last decade.¹³

Ultrasound has been recognized as a powerful diagnostic tool in many clinical settings beyond trauma and has proliferated through a variety of medical specialties. Although pioneered in emergency medicine, e-FAST has now become an important part of critical care evaluation of medical and surgical patients.¹⁴^,¹⁵

Limitations of e-fast

As an operator-dependent test, the learning curve, which is correlated with the results, has been studied. The literature describes variable outcomes related to different operators (radiologists vs. emergency medicine doctors). In addition, e-FAST is limited by technical factors that affect image acquisition, which include, but are not limited to, obesity and deep tissue structures, subcutaneous emphysema, bandages, or barriers to adequate transducer contact. Also, although sensitive for the detection of free fluid or air, ultrasound is not as adept in isolating the associated parenchymal injuries.⁵^,^16–19 Once free air or fluid is identified, additional imaging modalities, such as computed tomography (CT), are usually required to further isolate a parenchymal injury.

Application of e-fast in the intensive care unit

e-FAST is applicable in medical and surgical populations in the intensive care unit (ICU). The most practical applications concern hemodynamically unstable or shock patients in whom rapid diagnostic imaging, resulting in focused therapies, could potentially prevent catastrophic outcomes.

Learning to perform the e-FAST examination involves learning how to visualize the heart, diaphragms, liver, spleen, and bladder.²⁰ Interpretation of the e-FAST examination involves learning where free fluid commonly collects adjacent to these structures.

At this time, there is still lack of agreement on recommendations for e-FAST training. It appears that most investigators find that sensitivity and specificity begin to plateau after 25 to 50 examinations.¹⁸^,²¹ Current guidelines recommend performing 200 e-FAST examinations.²²

Thorax

Key findings

• Pneumothorax

• Free fluid

Of note, it has been demonstrated that 30% to 50% of pneumothoraces are missed by chest radiography.²³ This diagnostic inaccuracy is partially due to the fact that hemothoraces settle out posteriorly and pneumothoraces anteriorly. In the trauma setting, the e-FAST examination has a sensitivity of 81% to 100% and specificity of 100% for the diagnosis of free fluid in the thoracic cavity.²⁴ About 200 mL of free fluid in the thoracic cavity need to be accumulated to be detected by a plain chest radiography.²⁵ However, ultrasound is much more sensitive and is able to detect as little as 20 mL of free fluid in the same settings.²⁶ The time required for ultrasound versus radiography, in one study, was 1 minute versus 14 minutes, highlighting the potential for rapid diagnosis and intervention.²⁷ Although no similar studies are done for ICU patients, our clinical experiences fully support the time savings associated with bedside ultrasound.

Structures to be identified during the thoracic examination are the pleural line (the combination of the visceral and parietal pleura) and the costal arcs. Chest examination consists of defining “pleural sliding,” A-lines, B-lines, and free fluid (these specific findings are extensively detailed in previous chapters).

Anterior pneumothorax can often be undetected on a supine portable chest radiograph due to underlying normal lung tissue. However, it can easily be detected with ultrasound as air rises to the highest point within the chest cavity. Therefore, in a supine patient, free intrathoracic air will likely be detected in an anterior examination unless pleural loculations are present. Furthermore, presence of a lung point will be diagnostic of pneumothorax.²⁸

Detection of fluid in the thoracic cavity should promote acute interventions, such as rapid bedside thoracentesis, to determine the gross presence of blood and can facilitate chest tube placement in efforts to resuscitate an unstable patient (Figure 45-1).