Introduction and Background
Acute chest pain and dyspnea are common complaints amongst emergency department (ED) and intensive care unit (ICU) patients. These complaints account for several million annual ED visits in the United States. The list of potential diagnoses is exhaustive and critically ill patients can appear relatively well, potentially misleading the clinician. Common etiologies are of a cardiac and pulmonary nature, but also the gastrointestinal and musculoskeletal systems are frequently involved.
Physical examination and history taking are often nonspecific and clinical data such as blood pressure, heart rate, and oxygen saturation might not always reflect the true extent of the disease process. Conventional diagnostic tests such as electrocardiogram, chest x-ray, and laboratory data are initiated during the early evaluation phase, but results are not always readily available nor will they always determine the cause of illness. In this challenging situation, the physician’s main goal is to distinguish cardiac from pulmonary or other causes and identify a potential life-threatening illness as quickly as possible.
Bedside ultrasound can be indispensible in evaluating patients with unexplained chest pain or dyspnea. It can add vital clinical information in a matter of minutes and is often performed simultaneously with first resuscitation efforts and other medical procedures at the patient’s bedside. Ultrasound will often guide medical management and patient disposition.
Common sonographic exams utilized in such patients are pulmonary and cardiac ultrasound as well as point-of-care abdominal and vascular exam techniques. The specific sonographic exam protocols for these applications have already been discussed in previous chapters. This chapter describes an algorithm incorporating bedside ultrasound into the evaluation of ICU and ED patients presenting with acute undifferentiated chest pain or dyspnea.
Thoracic ultrasound has been shown to be highly efficient in diagnosing diseases such as pneumothorax, hemothorax, pleural effusions, pulmonary edema, pneumonia, and pulmonary embolism. In addition, other advanced applications of lung ultrasound, including acute respiratory distress syndrome (ARDS), pulmonary fibrosis, and carcinoma, although not easily diagnosed at the bedside, are currently being investigated in the critical care setting.
Physicians are familiar with the sonographic evaluation of the chest for pneumothorax and hemothorax, as this technique is part of the extended focused assessment with sonography for trauma (E-FAST) protocol. In patients with a clinical suspicion for pneumothorax, physician-performed lung ultrasound is more sensitive and specific than bedside chest x-ray when a cluster of sonographic features are evaluated, such as lung sliding, B lines, and the lung point sign. Furthermore, lung ultrasound has been found to be highly sensitive in the detection of radio-occult pneumothoraces and has been considered an alternative imaging modality to computed tomography in certain instances.
There are no clinical trials evaluating the utility of chest sonography in the diagnosis of tension pneumothorax published to date. The fact that tension pneumothorax is a clinical diagnosis and that physicians initiate needle thoracostomy immediately without reassuring imaging certainly contributes to this fact. However, there is an ongoing debate as to whether lung ultrasound should complement lung auscultation in a cardiac arrest situation, where ambient noise levels at the scene could limit auscultation findings and mask potential reversible causes of pulseless electrical activity arrest such as tension pneumothorax.
Ultrasound is also an excellent tool to identify fluid collections in the pleural space resulting in dyspnea and chest pain. Pleural effusions result from medical disease or traumatic hemothorax. They most often appear as homogeneously anechoic areas in the pleural space, but can also take on an echogenic pattern or appear as heterogenous septated or nonseptated areas between the two pleural layers. Small pleural effusions, as little as 5 cc, are consistently demonstrated with lung ultrasound, while being missed on chest x-ray.
The detection of the “fluid color sign,” a color Doppler signal that appears within a pleural fluid collection during cardiac and respiratory cycles, has been demonstrated to help diagnose very small effusions or loculated fluid collections.
Sonography can also be helpful in distinguishing between pleural transudate and exudate and has been used to accurately estimate pleural fluid volume. Transudates are most often a clear-appearing effusion without echogenicity, while exudates are hyperechoic and can contain mobile particles or septae suggestive of purulent pleurisy or hemothorax. One should remember, however, that exudates can be hypoechoic as well.
If there is suspicion for pulmonary embolus, bedside echo can be performed to evaluate for signs of acute right heart strain and acute pulmonary hypertension. Findings such as right ventricular dilatation with thin ventricular walls, right ventricular hypokinesis with apical sparing (McConnell’s sign), tricuspid regurgitation, and abnormal septal wall motion support the diagnosis, but it is important to note that these findings can be found in other disease entities. Clearly, visualization of a clot within the vena cava, right heart, or proximal pulmonary artery confirms the diagnosis.
The use of transthoracic sonography to identify peripherally located pulmonary emboli has also been described in the literature. The detection of two or more typical triangular or rounded pleural-based lesions on ultrasound has been reported to have a high specificity for pulmonary embolism.
In addition to the traditional physical exam, bedside ultrasound has been shown to be valuable in distinguishing between patients with an exacerbation of chronic obstructive pulmonary disease (COPD) and pulmonary edema in congestive heart failure (CHF). This clinical distinction can be particularly difficult in certain populations, such as the elderly, where cardiac and respiratory disease often coexist.
The detection of comet tails, also called “B-lines,” a sonographic artifact becoming more prominent with increasing interstitial pulmonary edema, can diagnose CHF with high accuracy while virtually ruling out COPD as the cause for acute dyspnea. Bedside echo to assess for overall cardiac function, which would be decreased in the situation of CHF, can also be beneficial in this situation.