Introduction

A 55-year-old businessman collapses while giving a presentation at a meeting. The medics find him to be breathing shallowly with barely obtainable blood pressure. They establish intravenous access, and transport him immediately to the closest emergency department. The ED team quickly generates a differential diagnosis of the conditions that may have caused the patient's collapse. This includes myocardial infarction complicated by cardiogenic shock, right ventricular infarct or rupture with pericardial tamponade, tension pneumothorax, ruptured aortic aneurysm, and pulmonary embolus. Initial work-up includes telemetry and electrocardiogram, which shows a sinus tachycardia without signs of infarct. The physical exam reveals a diaphoretic, critically ill patient with symptomatic hypotension, diminished breath sounds, and a distended, obese abdomen. The patient is simultaneously being resuscitated with saline bolus infusion and supplemental oxygen. He remains hypotensive.

This patient needs a diagnosis to initiate appropriate therapy, and soon. The problem is that the tools immediately available to the ED physician for making the diagnosis for this patient are limited to the history and physical exam, ECG, and radiographs. ECG is helpful in identifying patients with AMI, and may suggest pulmonary embolism. Chest radiograph will confirm suspicion of cardiogenic shock if there is pulmonary edema and will definitely diagnose pneumothorax. The remaining diagnoses cannot be arrived at without further testing or empiric therapy based on the clinical suspicion. This means that the patient usually will have to leave the ED for additional imaging studies, such as CT scanning, await the arrival of consultants to perform studies, or commit to take the patient to OR for exploratory surgery. For a patient who is as critically ill as this patient is, leaving the confines of the ED where he can be safely monitored is always risky. Every ED physician has their own anecdotal horror story of attempting to resuscitate a dying patient in the CT scanning room, and is loathe to transport an unstable patient out of the department. What are the options?

Ultrasound in the Emergency Department

ED physicians need a test that can be performed at the bedside and can rapidly confirm or exclude a finite number of life-threatening conditions that usually elude the screening of ECG, exam, and plain radiographs. This niche is more than adequately filled by ultrasound. Ultrasound is an example of technology that has applications in the diagnostic work-up of adult and pediatric patients presenting with a wide variety of injuries and illnesses. The physician specialists who have been responsible for defining the use of this technology have been the radiologists, who have overseen the maturation of the technology over the past two decades. Recent years have seen other specialists use ultrasound in the clinical management of their patients, with cardiology the first to claim ownership of ultrasound in the form of diagnostic echocardiography. More recently, obstetricians have used ultrasound to monitor pregnancy, urologists to assess bladder, renal function, and rheumatologists to assess a wide variety of musculoskeletal conditions. Intensivists have discovered a role for ultrasound when performing invasive procedures; imaging the body cavity or vessel that is being punctured enhances performance and reduces complications.

Over the past decade, EM physicians have realized that ultrasound, when performed at the bedside by the treating physician, greatly enhances the physician's diagnostic capabilities. Why rely on taking a pulse when you can look directly at what the heart is doing? If aortic aneurysm is a concern, why not look directly at the aorta and measure it? When inserting catheters into veins, why rely on blind external anatomic landmarks to identify where the vein is? Using ultrasound, you can image the vessel throughout the procedure to ensure appropriate placement. If you are concerned about the location and viability of a first-trimester pregnancy, why not image the uterus directly?

The first published reports of ultrasound used by EM physicians appeared in the late 1980s and described the potential applications of ultrasound for assessment of patients presenting with a wide variety of complaints, including traumatic injuries, hemodynamic instability, nonspecific abdominal pain, and symptomatic first-trimester pregnancy. EM physicians quickly appreciated the value of bedside sonography, and courses designed to teach limited bedside ultrasound to EM physicians were formed. Statements from the leading political and academic societies in EM endorsed the use of sonography by EM physicians, and guidelines for the use of sonography by EM physicians were developed.

These early efforts to teach and promote the use of bedside ultrasound lead to a broader base of EM physicians using ultrasound, published reports describing the real clinical impact of EM physicians using ultrasound, and a rapidly expanding list of clinical uses for ultrasound in the emergency department. Companies making ultrasound machines realized that there was a new niche for the technologies and developed small, portable machines that could be wheeled about the emergency department and fit at the bedside. As EM physicians developed proficiency and experience, their use of this technology was heavily criticized by those specialties that have overlapping clinical uses for ultrasound, specifically radiology and cardiology. Their argument was that many of the clinical uses for ultrasound in EM were already covered by their services, and there was little to no rationale for EM physicians with "minimal" training to perform identical studies. These arguments essentially forced EM physicians to clarify how their use of ultrasound differed from that of the cardiologist, radiologist, and obstetrician.

There is no question that each specialty is expert in the clinical applications for which their practitioners routinely use ultrasound. Obstetricians and radiologists share expertise in describing the sonoanatomy of the female pelvic organs and developing fetus. Cardiology clearly is responsible for describing and promoting the wide range of clinical applications of echocardiography in caring for the patient with a host of cardiac illnesses. The radiologists continuously push the envelope by promoting new technologies and demonstrating how sonography can provide detailed images of organs and disease.

What distinguishes the emergency physician's use of ultrasound is the fact that the exam is performed and interpreted by the physician caring for the patient; it is focused on answering a single clinical question and performed at the patient's bedside. It not only will identify or exclude specific diagnoses, but it can be used to monitor a patient's response to treatment, provide direct guidance during procedures, and be performed repetitively during a patient's stay in the ED. The most widely accepted clinical indications for directed ultrasound in the ED are to ascertain whether:

• There is free fluid in the abdomen or thorax in trauma patients
• There is a viable intrauterine pregnancy in patients with first-trimester pregnancy bleeding and/or pain
• In a patient with acute abdominal or flank pain, there is evidence of renal obstruction or cholelithiasis or abdominal aortic aneurysm
• In a patient in PEA (pulseless electrical activity), to determine if the is heart contracting, or if there is a hemodynamically significant pericardial tamponade
• Vessels or fluid collections (pleural, pericardial, peritoneal, subcutaneous, or intra- or peri-articular) that need to be entered percutaneously are patent and/or easily accessible

Rarely are these studies stand-alone. They often need to be followed with a definitive study that will offer more-detailed information about the disease that is beyond the scope of the ED study. The goal of ED-directed sonography is to help establish a working diagnosis in the early stages of evaluation and to guide initial therapeutic interventions to stabilize the patient. Following stabilization, patients will often undergo additional diagnostic studies. This may be in the form of a repeat ultrasound to clarify findings on ED sonogram or obtain alternative diagnostic studies (CT scanning, MRI, or operative exploration) to identify pathology that is not clear on ultrasound. An example of this is the middle-aged patient who presents with acute, severe, poorly localizable abdominal pain. Often the history and physical exam alone for such patients are nonspecific and unlikely to point to one diagnosis. ED ultrasound, performed at the bedside, may indicate that the patients has cholecystitis - allowing for early initiation of antibiotics, pain medications, and surgical consultation with plans for a definitive ultrasound once the patients is stabilized and admitted. The ultrasound may show an AAA, and the patient, if hemodynamically stable, would undergo CT scanning with contrast instead. It may show hydronephrosis, which suggests a renal obstruction usually due to kidney stones. The patient can be treated specifically for pain due to renal colic and then undergo a spiral CT without contrast to confirm the diagnosis.

Returning to the middle-aged businessman who collapsed during his meeting, ECG revealed a sinus tachycardia without infarct, and chest radiograph showed an enlarged cardiac silhouette but no pneumothorax or congestive heart failure. The cause of his collapse remained unclear. Bedside ultrasound showed that he had hyperdynamic heart, without pericardial effusion, which quickly excluded a cardiac cause for his hypotension. His abdomen was imaged next and showed that while there was no free fluid in his abdomen, he did have a 7cm abdominal aortic aneurysm. This has most likely ruptured into his retroperitoneum and was the cause of his hypotension. The examination took five minutes to identify the cause, and the patient was taken to the operating room 15 minutes later for surgical repair of his aneurysm.

As illustrated in the previous scenarios, ultrasound can readily guide the diagnostic work-up and treatment of patients with acute conditions. The benefits of ultrasound at the ER bedside include earlier diagnosis of critical or painful conditions, faster initiation of lifesaving or symptom-reliving interventions, and streamlined diagnostic work-ups. In recent years, there has been a virtual explosion of ultrasound technology geared for emergency physicians. There are numerous machines presently on the market and in development that range from small, portable machines that can be carried about the ED to cart-based machines that fit at the bedside, and that also provide high-resolution images with Doppler/color-flow capability.

Ultrasound training is now a requirement of all emergency medicine trainees. There are training programs available to practicing emergency-medicine physicians throughout the country, and guidelines for ultrasound use, training, and quality improvement monitoring have been developed by the specialty. The potential applications for ultrasound use in the ED are growing, and EM physicians are finding new and novel uses for the technology in their practices, including assessment of musculoskeletal injuries, identification of deep-vein thrombosis, and numerous procedural applications. The one sentiment that has been stated repeatedly by physicians who have incorporated sonography into their practice is: "It makes me a better doctor."