Soundings: Fast Exam

 

On this dark and rainy evening you’ve been spared some of the walking well (who decide not to brave the elements) but there are enough extra URI’s and slip & fall victims to make up the difference. All of a sudden the blue lights go off and you hear the familiar sound of the paramedic radio alarm. A few minutes later you are receiving the report from your MICN on an inbound trauma activation. “Medics are ten and sixteen minutes out with two pedestrians struck at high speed by an SUV”, she barks. “The first patient is a 47-year-old man with a GCS of 13, a head contusion, abdominal tenderness and a femur deformity. Pulse 120, BP 110/90. The second patient is a 6-year-old girl with a GCS of 10, a scalp laceration, flail chest and generalized abdominal pain. Pulse 140, BP 80/40”.

“Here we go” you think to yourself as you wrap up some loose ends and head to the trauma bay.

The 47-year-old is the first to arrive and the medic gives the story. Bystanders say he was crossing the street with his daughter. They were in a mid-block cross walk and the first lane of traffic stopped. The driver of the car in the next lane supposedly didn’t notice and kept driving. The father was found 15 feet from the site of impact. He has a head injury with repetitive questioning, a diffusely tender abdomen and a closed femur fracture in a traction splint. Last BP is 100/palp and heart rate is 130 after a 500cc saline bolus.

This guy sounds sick and doesn’t look good. Airway and breathing are fine. He has a nice lump on his head, but his abdomen is what really concerns you. As soon as you finish your ABC’s and before the plain films have been shot you pull over the ultrasound machine and get this view of the abdomen. (IMAGE 1). Based on the vitals, the exam, and your ultrasound, the trauma attending decides to take the patient for an immediate laparotomy. Lines are in and the blood is in the lab. “As soon as they shoot the chest and pelvis X-rays let’s move!” the trauma attending commands.

  

The 6-year-old girl arrives seconds later. Her GCS is falling so you opt to secure her airway and intubate her. She’s sick. Her vitals are unchanged from the field, pulse 140, BP 80/40. You note a flail chest on the left and suspect a hemothorax, a lung contusion, and probably a splenic injury beneath the cracked ribs. The X-ray tech is busy in the other bay so you wheel over the ultrasound machine to see if you are right. Unfortunately, it looks like you are. Here are the images you get (IMAGE 2 & 3). You place a chest tube connected to an auto-transfuser. She ends up getting that blood, plus six more units 

from the blood bank before she is finished with her splenectomy and craniotomy.

 

 

 

 

 

 

 

 

 

 

 

 

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Image 1 is a suprapubic view and shows intraperitoneal free fluid behind the bladder. Image 2 shows free fluid in Morrison’s pouch. Image 3 shows a fluid collection in the hemithorax below the lung base. In the setting of trauma, especially in otherwise healthy patients, this fluid should be assumed to be blood. First introduced in 1971, the use of ultrasound to assess thoraco-abdominal trauma has since gained worldwide acceptance. In 1996 Rozycki et al. coined the term Focused Assessment with Sonography for Trauma (FAST) to encompass the goal directed scans used in trauma management today. Over 95% of emergency medicine residents are taught how to perform a FAST exam during their training, and Advanced Trauma Life Support (ATLS) protocols now advocate the use of the FAST exam during the evaluation of your trauma victims. Rapid clinical decisions can be made by correlating the vital signs, physical exam findings, and images obtained during the FAST exam. In most trauma centers, the FAST exam has replaced DPL in the assessment of blunt abdominal trauma and can now be used to help predict the need for imminent laparotomy. Ultrasound has been touted for its noninvasive nature, speed, repeatability and portability during resuscitations where time is of the essence. In addition, unlike the DPL, the FAST can be used to check for intra-thoracic injuries such as hemothorax, pneumothorax, and pericardial effusion. The only absolute contraindication to performing the FAST examination is when immediate operative management is clearly indicated, and a FAST examination would only delay transport to the operating room.

The American Institute of Ultrasound in Medicine (AIUM) and the American College of Emergency Physicians (ACEP) recently co-authored a Guideline for the Performance of the FAST Examination. These experts feel that the FAST exam is a proven and useful procedure for the evaluation of the trauma patient during the initial resuscitation phase, with the primary goal being the detection of large abnormal fluid collections that require immediate treatment. Created with expert input from both radiologists and emergency physician ultrasound experts, the FAST guideline includes indications for performing the examination, qualifications and responsibilities of the performing physician, specifications for individual examinations, documentation requirements, equipment specifications, quality control, and safety standards.

Vivek Tayal, MD, FACEP, Chair of the ACEP Section of Emergency Ultrasound and member of the AIUM, has stated that “The FAST Guideline reinforces ACEP’s ultrasound imaging criteria (http://www.acep.org). The exam gained further national and international prominence by its formal acceptance by AIUM, a national, multi-specialty organization. What is significant is the cooperative nature of the document and multi-year effort.” The FAST guideline is available on the AIUM website at http://www.aium.org. A summary of these guidelines appears below.

General: The FAST exam is proven and useful at the bedside during resuscitation of the seriously injured patient to rapidly evaluate the peritoneal, pleural and pericardial spaces for bleeding. Multiple planes should be scanned in each area to improve sensitivity and specificity. Delayed imaging or the use of the Trendelenberg position may improve sensitivity.

Cautions: There are no absolute contraindications to the FAST exam, however sensitivity is decreased in minor injuries, mesenteric injuries and in children. In addition, false positive scans may result when pre-existing medical conditions, such as ascites, ovarian cysts, VP shunts, peritoneal dialysis, pleural effusions, etc. result in abnormal fluid collection

Credentialing: Training and credentialing should be based on published standards of the physician’s specialty society. Privileges are based on the bylaws of the individual hospital.

Right Upper Quadrant View: Otherwise known as Morrison’s Pouch or the hepatorenal space. Uses the liver as a window to image for fluid in Morison’s pouch. The right paracolic gutter and the right lung base can be evaluated by directing the probe inferiorly and then superiorly.

Left Upper Quadrant View: Otherwise known as the perisplenic space. Uses the spleen as a window to image for fluid in the diaphragmatic-splenic space as well as the splenorenal and inferior renal pole. The left paracolic gutter and the left lung base can be evaluated by directing the probe inferiorly and then superiorly.

Suprapubic View: Uses the bladder as a window to image for fluid in the pouch of Douglas in women and in the rectovesicular space in men. Absolutely make sure both planes, sagital and transverse, are used.

Pericardial Subcostal View: Uses the left lobe of the liver just below the xyphoid process as a window to image the heart and pericardium. Asking the patient to breathe in while gripping the probe from above (to bring it close to the coronal plane) may improve the view.

Additional Views: Anterior Pleural Space Views and Parasternal Views may improve sensitivity for detecting a pneumothorax or cardiac abnormalities. Pericolic Gutter Views may occasionally improve sensitivity for free fluid but are difficult to visualize due to the lack of a good acoustic window.
Documentation: Findings should be documented and if feasible, images should become part of the medical record.

Infection Control: Be sure to clean the ultrasound probe with an appropriate cleanser between uses.

 

continue next for Ultrasound Pearls and Pitfalls 

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•    Know your limitations: Ultrasound may help clarify findings elicited by a thorough history and physical exam.  When used correctly, it can greatly improve diagnostic accuracy, and help guide patient management, especially for time-critical diagnosis and treatment of unstable patients.  If you use ultrasound in your ED, your department should have a quality improvement program set up that is approved by both ED administration and radiology.

•    Remember that certain serious traumatic injuries cannot be detected with the FAST exam.  Because the exam is limited to four basic views, you will not be able to detect renal pedicle injuries, viscus perforation, bowel wall contusions, pancreatic trauma, diaphragmatic injury, or retroperitoneal injury. Generally FAST rules in injury, but does not rule out injury.

•    The amount of time lapsed between the inciting trauma and the FAST examination should always be taken into account. Blood appears anechoic (black) when acute and free flowing, but becomes less anechoic and more hypoechoic (gray) when subacute or clotted. Subacute blood may adhere to surrounding tissue and will not layer out as well as fresh blood.  This, coupled with its hypoechoic appearance may lead to false negative scans.  Blood in the pericardial space due to acute trauma may also appear gray secondary to decreased fibrinogen levels.  (Go to the Ultrasound Library via EPMonthly.com to see an image of this). 

•    The sensitivity of ultrasound in trauma improves with Trendelenberg positioning, repeat imaging, and if you know how and where to look. For one, always look at the inferior tip of the liver, as it may be positive when Morrison’s pouch is not. Likewise, always visualize the infradiaphragmatic region just above the spleen.  Often times, free fluid will accumulate in the suprasplenic recess before it flows into the splenorenal junction.  Also, if the bladder is full, remember to turn down the gain during the suprapubic scan, otherwise enhancement behind the bladder may “white out” a small pocket of fluid.

 

•    Note that intraperitoneal fat can often appear relatively hypoechoic on ultrasound and can be mistaken for free fluid or a hematoma.  Verify its identity by evaluating its variation with respiration, analyzing its density on multiple views, and correlating its presence with the entire clinical scenario.

 

•     If you cannot see the heart at all on the parasternal view, consider a small anterior left-sided pneumothorax until proven otherwise. The chest film will not be sensitive enough. If the patient is going to the OR consider either going to chest CT first or placing a chest tube empirically if the patient remains unstable and must be rushed to surgery.

 

•    If you work in a trauma center and don’t have an ED dedicated bedside ultrasound machine yet, you should. Get together with the trauma surgeons and request the hospital buy one and put on a course to train or re-train your doctors.

 

•    Practice Makes Perfect: With bedside ultrasound there is no substitute for experience.  The more ultrasounds you do, the better you will be able to differentiate abnormal from normal, even when you may not be sure exactly what the abnormality is. Take a look at the abdomen and pelvis of the next ascites patient or peritoneal dialysis patient to see grossly positive windows (understand that the findings in acute trauma are much more subtle.) An image library of normal and abnormal ultrasounds helps immensely and EPMonthly.com can take you there.  Just go to EPMonthly.com, select “Departments”, chose “Real-Time-Readings” and click on the “Ultrasound Library” link. 

 

Check out Dr. Wu’s interactive FAST tutorial on emedhome.com: http://www.emedhome.com/features_archive_detail.cfm?SFID=050106&SFTID=news