Background & Indications

Transcription

1 Teresa S. Wu, MD, FACEP Director, EM Ultrasound Program & Fellowship Co-Director, Simulation Based Training Program & Fellowship Maricopa Medical Center Simulation Curriculum Director Associate Professor, Emergency Medicine University of Arizona, College of Medicine-Phoenix Background & Indications Why should you know how to perform the efast exam? o Studies have shown that up to 40% of patients with significant abdominal injuries may initially have a normal physical examination of the abdomen. o The efast exam provides you with critical information within a matter of minutes. o You can determine, non-invasively, and rapidly, whether the patient has intraperitoneal free fluid, a pericardial effusion, a hemothorax, or a pneumothorax. o You can make diagnoses quickly and expedite patient care. When do you use the efast exam? o With acute blunt trauma to the abdomen and torso. o With acute penetrating trauma to the abdomen and torso. o Trauma in pregnancy. o Pediatric trauma. Special situations where the efast is paramount? o Hemodynamically unstable patients. o Unexplained hypotension in the setting of an equivocal physical exam. o Patient s with limited physical exam findings secondary to habitus or issues with cooperation. o Multi-casualty incidents with multiple critical patients. o When other imaging modalities are not readily available. Numbers You Need to Know o Most studies tout sensitivities of 69-99% and specificities of % for the FAST exam. o When clinically appropriate, you may improve your sensitivity and specificity by placing patients in Trendelenburg position and scanning the right upper quadrant first (91% accuracy).

2 Page 2 of 21 o 100% sensitive for detecting pericardial effusions, hemothoraces, and pneumothoraces. o Remember that pediatric traumas don t always have hemoperitoneum associated with solid organ injuries. o In children, efast has a sensitivity range between 30-80% and specificity range between %. o On average it takes 2-5 minutes to perform an efast exam. o You can see as little as 100 ml of intraperitoneal free fluid on ultrasound. Sonographic Principles o The appearance of hemorrhage will evolve over time. o Blood initially appears anechoic or black on ultrasound. o Clot begins to form in the first 4 hours and the blood appears more echogenic and grey. o Within hours, fibrinolysis ensues and blood reverts back to a more hypoechoic appearance. o Blood will layer around the bowel and viscera, and trickle down to the most dependent portions of the abdomen where folds are formed by peritoneal reflections and mesenteric attachments. Probe Selection Use the low frequency (3-5 MHz) curvilinear transducer (Image 1) or low frequency (3-5 MHz) phased array transducer (Image 2) Image 1: Low frequency curvilinear transducer. The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

3 Image 2: Low frequency phased array transducer to get in between tight rib spaces. Page 3 of 21 Performing the Scan If the ultrasound system is set for standard abdominal presets, the orientation marker on the monitor will be on the left side of the image. In this arrangement, the indicator marker on the probe should be oriented either cephalad or towards the patient s right side during the scan. Most of the time, the trauma patient will be lying supine, with blood accumulating in the most dependent positions. These areas include Morison s pouch (right hepatorenal fossa) and the retrovesicular space in men or the Pouch of Douglas in women. During the abdominal portion of the efast exam, utilize four primary views to identify free fluid (Image 3): Image 3: Probe placement and sonographic planes needed for performing an efast examination. Note the suprapubic view should be evaluated in both the transverse as well as the sagittal planes. The pericardial view is often obtained with the subxiphoid view, however, other views, most commonly the parasternal long axis view, may also be used. The images and pictures in this handout are copyright protected.

4 Page 4 of 21 o RUQ Overview (Morison s Pouch or the hepatorenal view): Visualizes the interface between the liver and Gerota s fascia of the right kidney. Interface resides at the vertebral level between T10 & L3. Long access of the interface runs almost parallel to the body. The renal fascia (Gerota s fascia) encloses the perirenal fat and the fibrous renal capsule of the kidney. The descending part of the duodenum passes across the hilum of the anterior-inferior portion of the right kidney. The suprarenal, duodenal, and colic areas of the kidney are not covered by peritoneum and create a potential space. The hepatorenal recess is the potential space between the anterior-lateral pole of Gerota s fascia and the overlying inferior surface of the liver. Note that Gerota s fascia is continuous superiorly with the inferior fascia of the diaphragm, so the level of the hepatorenal interface may vary up to 3 cm with respirations. Often times, the adrenal gland covering the anteromedial aspects of the superior pole of the right kidney may be visualized with a RUQ scan. Do not mistake this structure for free fluid. o Scanning the Right Upper Quadrant (Morison s Pouch): Visualizes the interface between the liver and Gerota s fascia of the right kidney. Place the probe with the indicator marker oriented towards the patient s right shoulder at the 7 th or 8 th intercostal space, near the mid-axillary line (Image 4). Orient the probe marker cephalad and slightly posteriorly so that the probe is placed within an intercostal space, thereby minimizing rib shadows on the image obtained. Recall that the rib cage curves inferiorly as you move from posterior to anterior. Use the liver parenchyma as your sonographic window. The bright white line of Gerota s fascia will lie flush against the liver parenchyma with a negative/normal exam (Image 5). A positive exam for free fluid in Morison s pouch will reveal an anechoic (black) stripe between the echoic (white) stripe of Gerota s fascia and the liver parenchyma. You may need to utilize intercostal spaces cephalad or caudad in order to achieve a clear view of Morison s pouch. Attempt to visualize the echoic (white) diaphragm cephalad to the liver to evaluate for fluid in the lung base. Asking the patient to inspire deeply will bring the diaphragm into view. The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

5 Image 4: Curvilinear probe position to obtain a view of the hepatorenal fossa Page 5 of 21 Image 5: Normal hepatorenal fossa. Liver Diaphragm Kidney o LUQ Overview (Perisplenic or the splenorenal view): Visualizes the interface between the spleen and Gerota s fascia of the left kidney. # Interface resides at the vertebral level between T11 & L2. # Long access of the interface runs almost parallel to the body. # The renal fascia (Gerota s fascia) encloses the perirenal fat and the fibrous renal capsule of the kidney. # Anterior to the left kidney lie portions of the stomach, spleen, pancreas, jejunum, and descending colon. # The splenorenal (aka lienorenal) ligament attaches the superior pole of the left kidney anterolaterally to the spleen. # The spleen is completely surrounded by peritoneum except at the hilum where the splenorenal ligament attaches. # Fluid may accumulate in the splenorenal recess representing the junction between the spleen and left kidney adjacent to The images and pictures in this handout are copyright protected.

6 Page 6 of 21 the splenorenal ligament; however, it usually collects first between the spleen and the diaphragm. Free fluid may also be visualized coursing along the superolateral pole of the spleen under the peritoneum below the left diaphragm. Note that Gerota s fascia is continuous superiorly with the inferior fascia of the diaphragm, so the level of the splenorenal interface may vary up to 3 cm with respirations. Often times, the adrenal gland covering the anteromedial aspects of the superior pole of the left kidney can be visualized with a LUQ scan. Do not mistake this structure for free fluid. o Scanning the Left Upper Quadrant (Perisplenic): Visualizes the interface between the spleen and Gerota s fascia of the left kidney. Place the probe with the indicator marker oriented towards the patient s left shoulder at the 8 th or 9 th intercostal space, in the posterior axillary line (Image 6). In order to use the spleen as a sonographic window, the head of the probe will have to lie more posteriorly than it did on the contralateral side because the spleen is a much smaller sonographic window. Angle the direction of the beam from posterior to anterior. This is a much more difficult window than the Morison s pouch view. Occasionally the patient will need to be rolled slightly onto his or her right side to allow for optimal visualization of the target organs. Orient the indicator marker cephalad and slightly posterior in a slightly oblique orientation. This will penetrate directly through the intercostal space and minimize rib shadows. Recall that the rib cage curves inferiorly as you move from posterior to anterior. The bright white line of Gerota s fascia will lie flush against the spleen with a negative/normal exam (Image 7). A positive exam for free fluid in the perisplenic recess will reveal an anechoic (black) stripe between the echoic (white) stripe of Gerota s fascia and the spleen or between the thick white dome of the diaphragm and the spleen. You may need to utilize intercostal spaces cephalad or caudad in order to achieve a clear view of perisplenic recess. Attempt to visualize the echoic (white) diaphragm cephalad to the spleen to evaluate for fluid in the lung base or free fluid between the diaphragm and the spleen. Asking the patient to inspire deeply will bring the diaphragm and the suprasplenic window into view. The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

7 Image 6: Curvilinear probe position to obtain a view of the splenorenal fossa Page 7 of 21 Image 7: Normal splenorenal fossa. o Suprapubic Overview (Pelvic or Pouch of Douglas in women): Identifies the rectovesicular pouch in males, and the cul-de-sac in females. # An empty bladder will lie almost entirely in the pelvis minor, inferior to the pelvic floor and posterior to the pubic symphysis. # With a full bladder, the sonographic window may rise as high as the umbilicus. # In the female, the bladder peritoneum is reflected from the superior-posterior surface of the bladder onto the anterior wall of the uterus, at the junction of the uterine body and cervix. # This reflection of peritoneum creates a recess called the vesicouterine pouch, or Pouch of Douglas. The images and pictures in this handout are copyright protected.

8 Page 8 of 21 In the male, the bladder peritoneum is reflected posteriorly towards the rectum, forming a recess called the rectovesicular or retrovesicular pouch. The vesicouterine pouch in females and the rectovesicular pouch in males communicate directly with the paracolic and infracolic gutters superiorly, such that free intraperitoneal fluid from any abdominal level may gravitate and accumulate in the recesses. o Obtaining the Suprapubic View (Pelvic or Pouch of Douglas in women): Identifies the rectovesicular pouch in males, and the culde-sac in females. Place the probe in a transverse orientation across the patient s suprapubic region, and aim it down into the pelvis, with the indicator marker pointing towards the patient s right side (Image 8). Using the bladder as your sonographic window, attempt to visualize the space farfield (posterior) to the bladder (Image 9). Free fluid in the pelvis will appear as an anechoic (black) stripe posterior to the bladder. Rotate your probe 90 cephalad and obtain a longitudinal view of the bladder and surrounding structures. The longitudinal view will help delineate the uterus in women and the prostate in men. Perform the suprapubic exam prior to placement of a Foley catheter so you don t lose your sonographic window. You may also fill the bladder in a retrograde fashion using normal saline if the Foley has already been placed and repeat scans are required. At times, the rectum can appear as a fluid filled anechoic structure sitting behind the bladder wall. If there is question as to whether the anechoic fluid collection is free fluid or simply an enlarged rectum, attempt to delineate whether of not the fluid collection layers out with patient movement. Free fluid should be seen extending laterally in the pelvis when the patient is tilted onto his or her side. Do not miss subtle or small fluid collections. Visualize the entire space surrounding the bladder by fanning through the entire organ superiorly, inferiorly, and from one side to the other. The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

9 Page 9 of 21 Image 8: Curvilinear probe position to obtain a view of the retrovesicular space. Image 9: Normal retrovesicular space in a male patient. Note the the probe is in a transverse plane with the indicator oriented towards the patient s right side. Bladder Retrovesicular Space o Cardiac Overview (Pericardial): Either subxiphoid (using the liver as a window) or intercostal (parasternal) views of the pericardium can be obtained. # The pericardium is a double-walled fibroserous sac made up two parts: a tough fibrous pericardium externally, and the double-layered sac of transparent membrane called the serous pericardium internally. # The parietal surface of the serous pericardium is fused with the fibrous pericardium, and the deeper visceral serous pericardium is reflected on the heart where it forms the epicardium. The potential space between the parietal and The images and pictures in this handout are copyright protected.

10 Page 10 of 21 visceral layers of the serous pericardium is called the pericardial cavity. This conical pericardial sac is located in the middle mediastinum, posterior to the body of the sternum and the 2 nd to 6 th costal cartilages, and anterior to the 5 th through 8 th thoracic vertebrae. Both blunt and penetrating trauma can cause bleeding into the pericardial cavity between the double-layered serous pericardium. The inferior diaphragmatic surface of the heart is comprised mainly of the right ventricle and a small portion of the left ventricle. The fibrous pericardium on the inferior surface of the heart is fused with the central tendon of the diaphragm and thus, the appearance of the pericardial sac is influenced by respiration. Small effusions may layer posteriorly with the patient lying supine, whereas large effusions (>300 cc) will be visible in the anterior and posterior portions of the pericardial cavity. o Obtaining the Pericardial View: Either subxiphoid (using the liver as a window) or intercostal (parasternal) views of the pericardium can be obtained. Place the curvilinear probe in the epigastric region, just to the right of the xiphoid process (Image 10). Have the reference marker on the probe oriented towards the patient s right shoulder, and aim the ultrasound beam towards the patient s left shoulder. Obtain a coronal view of the patient s heart by placing the probe flush against the patient s skin. Apply direct pressure on the body of the probe so that the face of the probe remains perpendicular to the patient s skin and the ultrasound beams are directed under the patient s rib cage. In the coronal view, all four chambers of the heart will be visualized. The right ventricle will be the anechoic chamber appearing nearfield on the screen (Image 11). Watch the pericardium through several cardiac cycles and evaluate for small pericardial effusions in the posterior pericardial sac. Having the patient inspire deeply will bring the entire pericardial sac into view. If you do not obtain an adequate subxiphoid view (i.e. the patient is obese, has a barrel-chest, or has too much abdominal pain), utilize the intercostal (parasternal) view. For the intercostal (parasternal) view, place the probe in the 2-4 th intercostal space, just to the left of the sternum, with the The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

11 Page 11 of 21 reference marker pointed towards the patient s right shoulder. # Aim the beam posteriorly, perpendicular to the chest wall. # A positive pericardial exam will show an anechoic (black) stripe of fluid between the echoic (white) fibrous pericardium and the chambers of the heart. Image 10: Probe placement for a subxiphoid view of the heart during an efast exam. Image 11: Subxiphoid ultrasound of the heart and all four chambers. The extended focused sonography of trauma (efast) incorporates the use of bedside ultrasound to evaluate the thorax for a pneumothorax or a hemothorax. The images and pictures in this handout are copyright protected.

12 Page 12 of 21 To perform an ultrasound to evaluate for a pneumothorax, use the linear array transducer and look into the patient s thorax at the 2 nd to 3 rd intercostal space in the mid-clavicular line. The probe can be oriented in a longitudinal fashion with the indicator marker pointing towards the patient s head, or in a transverse fashion with the probe marker pointing towards the patient s right (Image 12). Image 12: Probe placement to evaluate the lungs for a pneumothorax during the exam. Visualize the hypoechoic ribs of the chest wall. Identify the bright white pleural line just farfield to the ribs (Image 13). Image 13: Ultrasound image of the hypoechoic ribs and hyperechoic pleural line. Watch the parietal and visceral pleural interface during the respiratory cycle. Normal lung parenchyma will demonstrate lung sliding and comet tails (Image 14). The images and pictures in this handout are copyright protected.

13 Page 13 of 21 Image 14: Normal lung ultrasound with hyperechoic comet tails coming off the pulmonary pleura. If there is a pneumothorax with air trapped between the parietal and visceral pleura, there will be a paucity of lung sliding and no comet tails will be seen. On M-mode, normal lung will appear like the seashore sign, whereas a pneumothorax will show up like a barcode or stratosphere sign. Image 15: Normal lung in M-mode demonstrating the seashore sign (left). Pneumothorax in M-Mode demonstrating the barcode or stratosphere sign (right). The images and pictures in this handout are copyright protected.

14 Page 14 of 21 Normal Sonographic Anatomy Image 16: Normal right upper quadrant (RUQ) ultrasound. Image 17: Normal left upper quadrant (LUQ) ultrasound. Image 18: Normal pericardial scan (subxiphoid view through the liver). The images and pictures in this handout are copyright protected.

15 Page 15 of 21 Image 19: Normal pericardial scan (parasternal long axis). Image 20: Normal pelvic scan (male). Image 21: Normal pelvic scan (female). The images and pictures in this handout are copyright protected.

16 Page 16 of 21 Image 22: Normal lung and diaphragm interface. Image 23: Normal lung pleura (B-mode on the left and M-mode on the right). Notable Pathology Image 24: Free fluid in the right upper quadrant (RUQ). The images and pictures in this handout are copyright protected.

17 Page 17 of 21 Image 25: Free fluid in the left upper quadrant (LUQ). Image 26: Pericardial effusion surrounding the heart on a subxiphoid view. Image 27: Pericardial effusion surrounding the heart on a parasternal long axis view. The images and pictures in this handout are copyright protected.

18 Page 18 of 21 Image 28: Free fluid in the male pelvis. Image 29: Free fluid in the female pelvis. Image 30: Hemothorax seen above the liver. The images and pictures in this handout are copyright protected.

19 Page 19 of 21 Image 31: Lung Point: transition between pneumothorax and normal lung in M- Mode. Image 32: Liver laceration. Image 33: Splenic crush injury with free fluid seen superior to the spleen. The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

20 Page 20 of 21 Pearls and Pitfalls for Performing an E-FAST Exam Over time, older blood will become less anechoic and may appear as a dark gray stripe on your FAST exam. It may also begin to clot and will not layer out as well as fresh blood. Eventually, blood may become the same echogenicity as surrounding organs. Train your eyes to become accustomed to the smooth homogeneous appearance of the liver and spleen. Even in the absence of free fluid a heterogeneous appearance may signify a solid organ rupture with clotted blood. Morison s Pouch is the most dependent position when the patient is lying supine, so begin the efast exam with a RUQ view unless you are concerned about the possibility of cardiac tamponade. Be sure to look through the entire liver and kidney, both superior and inferior, medial and lateral, as small amounts of free fluid may appear in atypical locations. Placing the patient in slight Trendelenburg may guide free fluid to accumulate in the hepatorenal and splenorenal recesses, thereby enhancing your study. Visualize both the hepatorenal and splenorenal views through a few inspiratory cycles to ensure the absence of a large hemothorax or diaphragmatic rupture. Although rare, it is possible to catch a diaphragmatic rupture during a RUQ or LUQ scan. Always attempt to scan through the entire target organ in order to visualize fluid accumulating in atypical anatomic locations. If the patient recently urinated, you may need to instill normal saline into the empty bladder via a Foley catheter to enhance your sonographic window. Approach organs from posterior angles if bowel gas is occluding the views. Patients who are obese may have significant amounts of perinephric fat, which appears sonographically hypoechoic, and may lead to a falsepositive reading. Remember that free fluid will move with patient repositioning. Consider performing serial exams in patients in which you have a high clinical suspicion for intra-abdominal injury or in patients where bowel gas obstructed earlier views. Take your time to perform a careful study and produce good sonographic pictures. The acronym FAST was not meant to describe the speed of the study. If the clinical scenario changes, repeat the exam The images and pictures in this handout are copyright protected. Please do not copy or distribute them without written consent from the author.

21 Page 21 of 21 For more bedside ultrasound tips and tricks, check out the ultrasound app SonoSupport. The images and pictures in this handout are copyright protected.