Emergency Medicine News:
The Speed of Sound
Dr. Butts is the director of the division of emergency ultrasound and a clinical assistant professor of emergency medicine at Louisiana State University at New Orleans.
EMS brings a 65-year-old man to the ED complaining of shortness of breath. He has a history of congestive heart failure and COPD. He appears uncomfortable with marked tachypnea on arrival. His blood pressure is 160/90 mm Hg, heart rate is 120 bpm, respiratory rate is 45 bpm, and SpO2 is 90%. His breath sounds are diminished, and it is difficult to appreciate any additional sounds.
This type of patient is not uncommon in the ED. The challenge in this case is to tease out the etiology of the patient's severe dyspnea while treating him. Many of our patients carry multiple diagnoses that may cause shortness of breath, and they have vastly different treatment methods. Differentiating which illness is causing the acute presentation can be difficult, and many acute causes of dyspnea, such as cardiac tamponade and pulmonary embolism, require rapid diagnosis and treatment. Postponing treatment until receiving the results of adjunctive studies, such as CT, can result in deterioration of the patient's condition.
Ultrasound lends itself perfectly to these presentations; it can be used quickly at the bedside. Performing focused exams can be done in just a couple of minutes. Putting these exams together into an algorithm provides a straightforward pathway for the emergency physician to follow in examining these patients.
Similar to the RUSH protocol and FAST exam, several algorithms for the evaluation of acute dyspnea have been proposed in the literature. The BLUE protocol by Lichtenstein and Meziere was one of the first. (Chest 2008:134;117.) BLUE primarily evaluates the lung fields for sonographic evidence of pneumonia, pulmonary edema, and pneumothorax. The ETUDES protocol includes the measurement of brain natriuretic peptide combined with the presence of sonographic B-lines in the lung to confirm the diagnosis of cardiogenic pulmonary edema. (Acad Emerg Med 2009:16;201.)
The RADiUS protocol by Manson and Hafez expands on previous algorithms and incorporates cardiac, pulmonary, and IVC ultrasound to assess dyspneic patients. (Ultrasound Clinics 2011:6;261.) Utilizing these views, the authors formulated a clear algorithm. (See figure.) The exam begins with a focused cardiac exam to evaluate for pericardial effusion and evidence of cardiac tamponade, left ventricular function, and evidence of pulmonary embolism. The IVC is then assessed to determine its overall size and collapsibility as a marker of the patient's central venous pressure. Assessment for pleural effusion follows, and finally the pleura is assessed for signs of pneumothorax and for pleural artifacts that may indicate the presence of underlying pathology. Evaluation of the lower extremities for deep venous thrombosis is an optional addition to the protocol.
I will break down each of these components over the coming months and examine how to perform and interpret each section of the protocol.
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