Introduction To Emergency Ultrasound
A Review Of Justifications, Indications And Significant Findings

Steven A. Godwin M.D.
Steven A. Godwin, M.D. is Assistant Residency Director, Department of Emergency
Medicine at the University of Florida Health Science Center / Jacksonville.

Background

Ultrasound (US) has long been recognized as a powerful tool for use in the diagnosis and evaluation of many clinical entities. Over the past decade, as higher quality, less expensive scanners were developed, US has proliferated throughout various specialties. US is no longer limited to radiology but is being utilized by at least 8 different specialties. One specialty which has contributed new research regarding ultrasound's multiple clinical applications is Emergency Medicine. The attraction of immediate bedside sonographic examinations in the evaluation of specific emergent complaints makes it an ideal tool for the emergency specialist.

The social and economic pressures to triage, diagnose and rapidly treat patients, have fueled ultrasound's use as a primary screening tool in the Emergency Department (ED). Most institutions now utilizing emergency screening ultrasounds report faster turn around times and more expedient diagnosis of potential life-threatening emergencies such as internal hemorrhage following blunt trauma, abdominal emergencies, ectopic pregnancy, pericardial tamponade, and aortic aneurysms. One recent study found that with the use of emergency physician-performed pelvic ultrasound length of stay was decreased in the emergency department by a median of 120 minutes.1 In response to this demand, most emergency medicine residencies now train their residents in emergency screening ultrasound as part of their standard curriculum. This number is expected to climb to near 100% over the next several years as more programs gain hospital acceptance. The individual endorsement statements from both the American College of Emergency Physicians and the Society for Academic Emergency Medicine continue to support these advancements.2,3

What Is A Screening Ultrasound?

Emergency physicians now view screening ultrasonography as a tool, not unlike the stethoscope, as an instrument that we must be proficient in using. A screening ultrasound is, as the name implies, not a complete formal study. It is rather a highly focused, limited, goal directed exam with the expressed purpose of answering a select set of questions. Simply put, these are a list of primary examinations that may be critically time dependent and/or may show significant immediate benefit to the patient. These questions include: Is there a pericardial effusion present? Are there gallstones present? Is there hydronephrosis evident? Is there free peritoneal fluid? Is there a well-defined intrauterine pregnancy? Is there an abdominal aortic aneurysm (AAA) present? Is there a foreign body? Only in rare instances will these initial screens not be followed by a formal complete radiographic study in the next 1-2 days. Examples where this might occur include patients with pericardial effusion, intraperitoneal fluid or AAA sent immediately to the operating room.

Why now? Despite diagnostic US's proven benefits in Europe and now centers in the United States, its availability has always been limited because of both the size and cost of machines. Recently, technical advances have allowed high quality equipment to be developed and produced at a fraction of previous cost. Also, machines are now much smaller in size with some weighing less than 20 pounds. This allows the new machines to be easily moved around a busy emergency or trauma area without disrupting patient care, making US both a convenient and effective tool for any sized ED.

Are Screening Ultrasounds Safe?

Only in the past 10 years has the use of bedside emergency screening ultrasounds by Emergency Physicians begun to reach its full potential. This increased interest is largely due to the abundance of studies produced by institutions leading the way in emergency ultrasound. This research has provided overwhelming evidence that with limited training emergency physicians can safely, efficiently, and accurately use screening ultrasound. These studies have looked at a variety of emergent clinical presentations including blunt abdominal trauma,8-11 pericardial tamponade,12 uncertain cardiac activity or PEA,12 ectopic pregnancy,13-15 renal colic,16,17 cholelithiasis,13,18,19 AAA,13,20 as well as foreign body localization and removal.21

Types Of Screening Ultrasounds

The spectrum of emergency ultrasounds can be placed in the categories of abdominal, pelvic, cardiac, trauma and miscellaneous ultrasounds. In this next section I will briefly discuss the justification, indications and significant findings in each.

Abdominal Ultrasound

Abdominal pain is a frequent complaint in the ED and often requires a great deal of physician time and hospital resources to ensure an appropriate diagnosis and safe disposition. Primary examinations involving the abdomen are the screening exam of the gallbladder, abdominal aorta, and kidney.

Cholelithiasis -- The classic clinical presentation of cholelithiasis is well described as post-prandial right upper quadrant pain combined with point tenderness in that area. Unfortunately this picture often seems confused in the ED due to atypical presentations and/or the presence of multiple medical problems including diabetes and peptic ulcer disease. The vast majority of gallbladder disease is secondary to stone formation. In the United States, gallstones are found in at least 20% of women and 8% of men over the age of 40. Unfortunately, due to the stones' composition, most commonly mixed, they are visible on only 15% of plain films.22 Regardless of the calculi make-up they are normally very reflective to ultrasonic rays. Quite often the stones will create an acoustic shadowing affect distal to the stone itself (Figure 1). This finding is highly diagnostic for the presence of cholelithiasis. Other important ultrasonic findings of gallbladder disease include gallbladder thickening of greater than 3mm and a "Sonographic Murphy's sign". The Sonographic Murphy's sign is the elicitation of point tenderness beneath the probe upon pressure above the gallbladder. The sensitivity and specificity of this sign alone for the presence of cholecystitis has been quoted at 90%.23 In a matter of minutes with a bedside exam the physician is able to confirm or rebuke his clinical suspicions. The examining physician can then narrow the focus of the work-up or discharge the patient home with a planned formal examination and primary care visit. It is important to note the purpose of this screening exam is only to detect stones, not to identify intrahepatic pathology, pancreatic pathology or evaluate the common bile duct. All these findings are beyond the scope of a screening ultrasound.

Figure 1. This picture demonstrates gallstones (S) within the gallbladder. Note the acoustic shadowing (AS) created by the echogenic stones.

Abdominal Aortic Aneurysm -- Abdominal Aortic Aneurysm (AAA) is a condition which clearly meets all criteria for being considered as a primary ED ultrasound examination. Its rapid diagnosis is imperative for patient's survival. The patient who presents with abdominal pain radiating to the back, hypotensive with a pulsatile abdominal mass following a syncopal episode is not a diagnostic dilemma. However, as noted before, these classic presentations are few and far between. More often it is the elderly patient with vague abdominal complaints or the middle-aged patient with symptoms mimicking simple nephrolithiasis that are missed or have delayed diagnosis. Although angiography and contrasted CT are both more specific tests, ultrasound can provide a rapid and effective alternative. In cases where time and/or resources are limited as with an unstable patient or an already busy CT scanner, ultrasound is an ideal tool in the ED. A recent study presented at the Society for Academic Emergency Medicine's national conference showed a significant decrease in time to diagnosis resulting in markedly improved outcomes in patients with ruptured AAA. Specifically, the study found an average time to diagnosis with US of 5.4 minutes compared to 83 minutes in the retrospective control group. Also the authors discovered only a 12 minute lag time to surgical intervention in the US group versus 90 minutes in the control. Most importantly the study revealed a significantly improved mortality in the US group.20

Again this is simply a screening exam. Its goal is to evaluate for the presence or absence of an AAA (Figures 2A and 2B). Since the aorta is a retroperitoneal structure, US can only accurately evaluate for dilatation not rupture. Performance of the exam can be done at bedside in less than 5 minutes. Even in the busiest ED, this is time well spent from both a patient care aspect as well as a risk management issue. Obviously rapid evaluation and diagnosis can have a definite effect on patient outcome. This fact is even clearer when treatment of an aneurysm would require transportation to another facility. By providing an early diagnosis with a screening US, the patient avoids the 1-2 hour delay of obtaining a CT scan. There is no doubt that this skill is important to all emergency physicians but may be especially valuable to those practicing in rural communities.

Figure 2A (top). This view demonstrates a sagital view of an abdominal aortic aneurysm.

Figure 2B (bottom). This view is a transverse view of the same abdominal aortic aneurysm. All measurements of an aneurysm are based on the transverse view measurements.

Renal Colic -- The third indication for the primary sonographic examination of the abdomen is nephrolithiasis. Although renal calculi themselves are rarely seen on US, hydronephrosis is easily demonstrated. (Figure 3) Currently there are multiple ways to evaluate for the presence of renal stones. These include IVP, ultrasound and limited non-contrasted helical CT studies. Each of these studies has its pros and cons. It should be noted that both IVP and helical CT are more sensitive and specific for the identification of stones. However, limited US can rapidly determine the presence or absence of obstructive uropathy by evaluating for hydronephrosis. Although it is possible to have renal stones without signs of obstruction, prolonged pain normally occurs with ureteral and renal pelvis dilatation. Therefore, patients with well-defined pain and without dehydration, should have some degree of sonographic findings. This study is particularly useful in patients with dye allergies, renal insufficiency, congestive heart failure, suspected pregnancy and where non-contrasted CT is not an option. Even in institutions where helical CT is available, it may not be financially feasible or time efficient to delay patients in the ED 30- 90 minutes when a 5 minute bedside test may be diagnostic. From a medical-legal standpoint, the ability to confirm this diagnosis in older patients where AAA or mesenteric ischemia are also in the differential is extremely important. Once this diagnosis is confirmed by US, the management can begin with appropriate disposition and arrangement of urology follow-up. The patient is then able to leave the ED with a firm understanding of their diagnosis. At the same time, the physician has the comfort of now discharging the patient in a timely manner and a definitive diagnosis. Follow-up confirmatory radiologic studies as an outpatient would be appropriate in the next 2-3 days.

Figure 3. This view of the right upper quadrant demonstrates hydronephrosis (arrows) within the kidney (k). Notice the interface between the kidney and liver (l).

Pelvic Ultrasound

Pelvic ultrasound has been for many years an important tool in the evaluation of the pregnant female. This is now the standard of care in the evaluation of possible ectopic pregnancy for patients with first trimester pain or bleeding. Because of hospital resources at most institutions, after hours pelvic ultrasounds require that an ultrasonography technologist be "called in" from home. This often delays patient care from 30 minutes to over 2 hours. Due to the difficult nature of this exam, ED screening US is limited only to identifying a definite in utero pregnancy. This is true when utilizing trans-abdominal and endovaginal probes. There should always be a low threshold for obtaining an immediate formal study in females where the screening exam is not totally conclusive. This noted, studies by Shih, Mateer, and Durham have demonstrated that ultrasound trained emergency physicians can reliably determine the presence of intrauterine pregnancy (IUP). (Figure 4) As noted earlier, Shih et al demonstrated a significant decrease in ED stay of almost 120 minutes.1 More importantly, Mateer et al also showed a significant decrease in morbidity secondary to missed ectopics when the ED physician performed ultrasounds prior to patient discharge.15 This limited exam is not and should not be considered a complete formal evaluation in first trimester of pregnancy. But, when performed correctly, it can save both hospital resources and patient time by identifying an intrauterine pregnancy and allowing the patient to be safely discharged with follow-up evaluation and studies the next day.

Figure 4. The markers are demonstrating an 8 week fetus within the walls of the uterus.

Cardiac Ultrasound

Screening cardiac ultrasound evaluation is limited to the detection of cardiac activity in patients with pulseless electrical activity and the detection of pericardial effusion/tamponade.

PEA is defined as the presence of electrical cardiac activity in the absence of pulses. This does not necessarily mean that the heart is not beating. Multiple reasons relating to low-flow states including hypovolemia, peripheral vascular disease, tamponade, and tension pneumothorax may contribute to this finding. Simple rapid visualization of the heart wall allows the physician to assess for activity. If cardiac activity is discovered then rapid evaluation and correction of the low flow state may be life-saving.

Pericardial tamponade, although discussed in more detail in the trauma ultrasound review, certainly may and does occur in medical patients. Causes of this sometimes life-threatening diagnosis may include uremic pericardial effusion, pericardial effusion status post cardiac surgery or pericarditis. With the exception of hypotension, a patient's body habitus often makes the detection of muffled heart sounds and distended neck veins as per Beck's triad clinically difficult to appreciate. Rapid bedside ultrasound provides the Emergency Physician with the ability to quickly diagnose the presence of an effusion prior to onset of tamponade physiology (Figure 5). This event is marked sonographically by the collapse of the right atrial and/or ventricular walls during diastole. Obviously, in the right clinical setting, simple detection of pericardial fluid is enough to initiate immediate treatment. An example of this is the patient who is found in PEA. Normally, peri-cardiocentesis is a last effort in a presumably futile resuscitation. Intuitively, with early detection and correction of tamponade, a patient's chance of survival greatly increases.

Figure 5. This US image demonstrates a pericardial effusion between the arrows. The left arrow is sitting on the myocardial wall.

Focused Abdominal Sonography For Trauma (FAST)

Abdominal ultrasound has been used to evaluate trauma patients in Europe since the 1970's. The German surgery board has required certification in US skills since 1988. Over the last 10 years in the United States, the use of US in trauma has gone from non-existent in most centers to now essentially replacing diagnostic peritoneal lavage (DPL) in many centers. Most recently the FAST exam has been included as part of the Advanced Trauma Life Support (ATLS) course. In addition, The American College of Surgeons has included ultrasound as one of several "new technologies" that surgical residents must be exposed to in their curriculum. It is evident that to more rapidly evaluate blunt abdominal trauma, emergency physicians must become proficient in the use trauma ultrasound.

The FAST exam's only objective is the detection of free intraperitoneal fluid in blunt abdominal trauma. A CT scan provides excellent solid organ detail, but it is expensive and often requires transport of the patient outside the department. DPL is more sensitive for detecting intraperitoneal blood than US. It is usually considered positive with 100,000 RBCs/mm3 which is 20 ml of blood per liter of lavage fluid.24 US is reliably sensitive to usually greater than 250ml in Morrison's Pouch.25,26 DPL, however, is invasive and often complicated by pregnancy or previous surgery. US is inexpensive, rapid, and easily repeated. There is an overwhelming amount of current data supporting the use of the FAST exam as the initial screening tool for evaluation of the abdomen in blunt trauma.8-11 Since all hemoperitoneum does not need surgical intervention, further more specific studies such as CT scan may be warranted in stable patients. One algorithm for a clinical pathway in the evaluation blunt trauma has been adopted by a number of centers, including Jacksonville, for the use of US as the initial screening test. If positive, the unstable patient goes to the operating room, a stable patient is evaluated by CT scan. If the US is negative in the stable patient, no further exams are indicated unless the patient has severe abdominal pain or there is a change in the clinical condition. In these patients, further evaluation is indicated with repeat US, CT scan or laparotomy.

The FAST exam is performed by utilizing 4 views:

  1. Morrison's Pouch -- This image visualizes the right upper quadrant at the interface between the liver and Gerota's fascia of the kidney known as Morrison's Pouch (Figures 6A and 6B).
Figure 6A (top). This US image demonstrates a round view of Morrison's Pouch at the interface between Gerota's fascia of the kidney (k) and the liver (l). perinephric fat (f) can sometimes be mistaken as free-fluid.

Figure 6B (bottom). The free-fluid (arrows) outlining the liver in this view of Morrison's pouch demonstrates a positive study.

  1. Perisplenic View -- This view of the left upper quadrant visualizes the kidney and spleen interface (Figure 7).
  2. Pelvic View -- The third image identifies the rectovesicular pouch in males and the cul-de-sac in females utilizing both transverse and longitudinal views of the pelvis (Figure 8). This is the most sensitive of the abdominal views with less than 200 cc of fluid sometimes seen.
  3. The Pericardium -- The last view takes us outside the peritoneum to evaluate for pericardial effusion by placing the probe just to the right of the patient's xiphoid. The ultrasound beam is then focused through the liver thus visualizing the interface of the right ventricle and the pericardium (Figure 5).
Figure 7. This figure demonstrates free-fluid around the spleen (S) and above the kidney (K). Figure 8. This view of the pelvis shows the uterus (U) surrounded by free fluid (arrow).

Emergency physicians provide the primary stabilization of trauma victims in the vast majority of institutions without the benefit of a radiologist at bedside. This fact coupled with the reality that the morbidity and mortality associated with trauma increases the longer life-threatening injuries are left undiagnosed makes ultrasound a priceless tool for the ED physician treating the traumatized patient. Upon discovery of intraperitoneal fluid, the emergency physician can then mobilize the onsite surgery team or rapidly transfer the patient depending on the hospital's resources. Multiple studies have supported the use of trauma US by both ED physicians and surgeons. Training in the FAST exam ranges from only 2 hours to greater than 8 and 10 hours 7,10,5 with sensitivities/specificities of 75% / 96%, 81% / 99%, and 90% / 99% respectively.

One can not forget the limitations of this study and significant injuries can be missed even in the hands of the most experienced ultrasonographer. However, when used appropriately diagnostic US in trauma allows the emergency physician to rapidly assess, reassess and correctly disposition trauma patients.

Miscellaneous

Other potential uses of screening US include the detection of foreign bodies,21 an aid in difficult central line placement, detection of pleural effusions, and localization joint effusions in difficult arthrocentesis.

Training

Although some guidelines have been suggested by the governing bodies in Emergency Medicine for training there is at this time no set national standard. Therefore, instruction and credentialing should be institutionally dependent. Didactic training in studies has varied from 2-40 hours of lectures.3 The practical portion has ranged from 10 minutes to 40 hours of hands on training or from 3-100 proctored cases.3,14,27 The answer to what is adequate training is probably somewhere in the middle and involves 20-25 hours of didactics including technical training followed by 25-50 proctored exams per primary indication. These numbers are based on published data from practicing institutions.28-30

Conclusion

It is clear that emergency screening ultrasound is now a nationally accepted tool for the rapid assessment of the emergency patient. The ability to perform these focused studies will allow for a more expedient and safer disposition of patients. Length of stay in the emergency department dramatically decreases thus increasing patient satisfaction while maintaining an even higher standard of care. The elderly patient with the non-specific low back pain can be quickly screened by US and discharged without the risk of a missed AAA. Also, the awake young driver who presents following a MVA with transient hypotension can be quickly assessed and intraperitoneal bleeding rapidly identified. The disposition to the operating room is then determined in less than 5 minutes from arrival. In another example, the patient with presumed nephrolithiasis can be evaluated then sent home quickly and safely with follow-up studies and primary physician evaluation. In these case examples, better quality of care has translated into improved patient satisfaction as well as better risk management.

In these days of increasing litigation, it is important to both the individual physician and the hospital ensure that each patient is evaluated as thoroughly and timely as possible thus guaranteeing the highest level of customer services. Our patients in the emergency department demand and deserve efficient, safe, and accurate health care. As we move into the new millennium, screening US will lead the way for new and more cost effective technology in emergency centers around the country.

REFERENCES

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  2. American College of Emergency Physicians. Council resolution on ultrasound. ACEP News. Nov 1990.
  3. Mateer J, Plummer D, et al. Model curriculum for physician training in emergency ultrasonography. Ann Emerg Med. 1994; 23: 95-102.
  4. Jehle D, Guarina J, Karamanoukian H. Emergency department ultrasound in the evaluation of blunt trauma. Am J Emerg Med. 1993; 11(4):342-346.
  5. Ma J, Mateer J, Ogata M, et al. Prospective analysis of a rapid trauma ultrasound examination performed by emergency physicians. J Trauma. 1995;38:879-885.
  6. Ma J, Kefer M, Mateer J, et al. Evaluation of hemoperitoneum using a single and multiple view ultrasonographic examination. Acad Emerg Med. 1995:2(7)581-586.
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  9. Nordenholtz KE, Rubin MA, Gularte GG, et al. Ultrasound in the valuation and management of blunt abdominal trauma. Ann Emerg Med. 1997; 29(3):357-66.
  10. Thomas B, Falcone RE, Vasquez D, et al: Ultrasound evaluation of blunt of blunt abdominal trauma: Program implementation, initial experience, and learning curve. J Trauma. 1997; 42(3):384-8.
  11. Porter RS, Nester BA, Dalsey WC, et al. Use of ultrasound to determine need for labarotomy in trauma patients. Ann Emerg Med. 1997; 29(3):323-30.
  12. Corbett S, O'Callaghan T. Detection of traumatic complications of cardiopulmonary resuscitation by ultrasound. Ann Emerg Med. 1997; 29:317-322.
  13. Schlager D, Lazzareschi G, Whitten D, et al. A prospective study of ultrasound in the ED by emergency physicians. Am J Emerg Med. 1994; 12(2):185-189.
  14. Durham B, Lane B, et al. Pelvic Ultrasound performed by emergency physicians for the detection of ectopic pregnancy in complicated first-trimester pregnancies. Ann Emerg Med. 1997; 29:338-347.
  15. Mateer J, Valley V, Aiman E, et al. Outcome analysis of a protocol including bedside endovaginal sonography in patients at risk for ectopic pregnancy. Ann Emerg Med. 1996; 27:283-289.
  16. Brown D, Rosen C, Sagarin M, et al. Impact of bedside renal ultrasonography by emergency physicians on the clinical likelihood of nephrolithiasis. Ann Emerg Med. 1996; 27:818.
  17. Rosen C, Brown D, Sagarin M, et al. Ultrasonography by emergency physicians in detecting hydronephrosis in patients with suspected ureteral colic. Acad Emerg Med. 1996; 3:541.
  18. Rosen C, Brown D, Chang Y, et al. Ultrasonography by emergency physicians in diagnosis of cholethiasis. Acad Emerg Med. 1996; 3:541.
  19. Rosen CL, Brown DFM, Chang U, et al. Gallbladder Ultrasonograpy: Agreement Between Emergency Physicians and Radiologists. Acad Emerg Med. 1998; 5:417 (abstract).
  20. Plummer D, Clinton J, Matthew B. Emergency Department Ultrasound Improves time to Diagnosis and Survival in Ruptured Abdominal Aortic Aneurysm. Acad Emerg Med. 1998; 5:417 (abstract).
  21. Hill R, Conron R, Greiddinger P, et al: Ultrasound for the detection of foreign bodies in human tissue. Ann Emerg Med. 1997; 29:353-356
  22. Greenberger NJ, Isseleaucher KJ. Diseases of gallbladder and bile duct. In Harrison's Principles of Internal Medicine. Wilson JD, Braunwald E (eds), et al. New York, McGraw Hill, 1991;1358-1368.
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  26. Kawaguchi S, Toyonaga J, Ikeda K, et al. Five point method: An ultrasonographic quantification formula of intra-abdominal fluid collection. Japan J Acute Med. 1987; 7:993-997.
  27. Plummer D, Brunette D, Asinger R, et al. Emergency department echocardiography improves outcome in penetrating cardiac injury. Ann Emerg Med. 1992; 21: 709-712.
  28. Lanoix R. Credentialing issues in emergency ultrasonography. Emerg Med Clin North Am. 1997; 15:4.
  29. Lanoix R, Baker W, Mele J, et al. Evaluation of an instructional model for emergency ultrasonography. Ann Emerg Med. 1998;5.
  30. Tandy T, Hoffenberg S. Emergency department ultrasound services by emergency physicians: Model for gaining hospital approval. Ann Emerg Med. 1997; 29:367-374.
March, 1999/ Jacksonville Medicine

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