Background
A chest X-ray (CXR) is a noninvasive imaging procedure that uses ionizing radiation to produce a shadow image of the anatomic structures in the thoracic cavity. The term “X-ray” refers to the type of high-energy electromagnetic radiation used in the imaging procedure, which was discovered by the German physicist, Dr. Wilhelm Roentgen. A CXR is also known as a plain chest roentgenogram, a plain (chest) film, or a chest radiograph.
How to Use It
A CXR produces a two-dimensional image of the contents of the chest and nearby structures by beaming X-rays through the chest and onto a digital plate or film. Different tissues attenuate (absorb) the X-rays to varying degrees, producing an image based on the amount of radiation that reaches the digital plate. The higher the attenuation, the more radiodense (or white) an object will appear in the image ( Table 16.1 ). A CXR enables the clinician to diagnose multiple cardiopulmonary conditions, including pneumothorax, pulmonary edema, pneumonia, cardiomegaly, metastatic disease, aortic dissection, pericardial effusion, drug-induced pulmonary toxicity, and rib fractures. CXRs also provide useful information about the upper gastrointestinal tract, such as the presence of intraperitoneal air. , The presence and location of invasive devices, including central venous catheters (CVCs), endotracheal tubes, feeding tubes (oro- and nasogastric), pulmonary artery catheters, and chest tubes, are also visible on CXR. See Chapter: 37: Intravenous Access for details about CVCs. See Chapter 42: Nasogastric Tube for details. See Chapter 15: Chest Tube for details.
| Material | Radiographic Appearance | |
|---|---|---|
| Air | Black | |
| Fat | Dark-gray | |
| Water (Soft Tissue) | Light-gray | |
| Bone | Off-white | |
| Metal | White | |
How It Is Done
CXRs are quick, noninvasive, painless, and relatively inexpensive. Patients do not need to fast before CXR, and procedural sedation is usually not indicated, as shooting an X-ray takes only a fraction of a second to obtain an image. A rare exception is an agitated and combative trauma patient, who may require sedation before a bedside CXR can be obtained by the radiology technician. During CXR, patients are exposed to a low dose of radiation, approximately 0.1 mSv or the equivalent of 10 days of normal background radiation. CXRs can be taken from different views, which must be specified by the ordering clinician. For most indications, the posteroanterior (PA) view is preferred. The patient is asked to inhale deeply and stand with their chest against a film cassette, with an X-ray source located at the patient’s back ( Fig. 16.1 ). To better identify abnormalities obscured on the PA view, a left lateral view is also obtained ( Fig. 16.2 ) by turning the patient a quarter-turn to the left. A PA and lateral CXR can be obtained in the outpatient or inpatient setting in a radiology suite as long as the patient is stable and able to cooperate. Portable X-ray machines can also be used to obtain an anteroposterior (AP) view at the bedside. A radiology technician will place a film cassette behind the patient’s chest and a portable X-ray source in front of the patient’s chest. Again, full inspiration is preferable to better visualize the patient’s lungs. Compared with the PA view, the AP view increases cardiac magnification (artificially increasing heart size) and reduces anatomical resolution. , , After taking the CXR, the technician will upload the image to a picture archiving and communication system. The CXR will be interpreted by a radiologist who will document their findings in a written report. Non-radiologist providers caring for the patient may also review the CXR while awaiting the report.
There are many described methods for interpreting CXRs. Regardless of the chosen method, the most important factor is to use a systematic approach, as this will minimize diagnostic errors. Generally, the first step is to ensure the image is of the correct patient and of the correct date and time. Whenever possible, a previous CXR should be used as a comparator. Next, providers will assess the quality of the X-ray by noting the degree of inspiratory effort, the adequacy of X-ray penetration, and the positioning of the patient by checking that the trachea is midline and the clavicles appear straight. The reviewer should also inspect the lungs for signs of pulmonary infiltrates, assess the clarity of the costophrenic angles, evaluate for possible enlargement of the cardiac silhouette, and check for any rib fractures. The chest wall should be inspected for abnormalities, and the presence and location of any invasive medical devices should be noted. Many clinicians use a mnemonic such as “ABCDE” as part of their systematic approach to interpreting CXRs. While there are several versions, one example is A: airway, B: bones or breathing (lungs/lung fields), C: cardiac/mediastinum, D: diaphragm, E: everything else. A normal CXR will show a nondeviated, midline trachea, seven to nine unfractured ribs above the diaphragm (this number generally demonstrates adequate inspiratory effort without hyperinflation), clear costophrenic angles and lung parenchyma, and a normal-sized cardiac silhouette (see Figs. 16.1 and 16.2 ).
Medication Implications
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Patients who are unable to swallow often have an orogastric or a nasogastric tube placed to allow for enteral feeding and medication administration. After placement of the tube, its location must be confirmed on CXR before it can be used to administer tube feeds or medications. The tip of the tube should be approximately 10 cm past the gastroesophageal junction. See Chapter 42: Nasogastric Tube for details.
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There are several indications for CVC, including the administration of certain medications (e.g., hypertonic saline, total parenteral nutrition, vasopressors, chemotherapy). Except in emergency scenarios, the location of a subclavian or internal jugular placed CVC should be confirmed on CXR or ultrasound before it is used. The tip of the CVC should be in the superior vena cava, ideally just above the right atrium. See Chapter 37: Intravenous Access for details about CVCs.
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A CXR may indicate the presence of pulmonary edema, which can be further classified as cardiogenic or noncardiogenic.
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Cardiogenic pulmonary edema (CPE) is the result of elevated left-sided heart pressures (due to congestive heart failure, myocardial infarction, cardiomyopathy, arrhythmias, etc.) leading to increased pulmonary capillary pressure and fluid buildup in the lungs. CXR findings consistent with CPE include cardiomegaly, cephalization, bilateral and symmetric interstitial and/or alveolar edema, Kerley B lines, and pleural effusion ( Fig. 16.3 ). After initial stabilization of the patient, the mainstay of therapy for CPE is to correct any reversible underlying cause and provide intravenous (IV) loop diuretics. For patients who are using chronic diuretic therapy, the IV dose should be greater than or equal to their oral daily dose (e.g., if on furosemide 40 mg by mouth daily at home, administer furosemide ≥40 mg IV). If a patient is loop diuretic–naive, an initial dose of furosemide 20–40 mg IV (or an equivalent dose of bumetanide [0.5–1 mg] or torsemide [10–20 mg]) is appropriate. The diuretic can be given as intermittent boluses or a continuous infusion. Urine output and symptoms of fluid overload should be closely monitored with diuretic dose adjustments as necessary. If patients have an inadequate response to high-dose loop diuretics, a thiazide diuretic can be given 30 to 60 minutes before the loop diuretic to augment diuresis by preventing rebound sodium and fluid reabsorption in the distal tubule. Vasodilators and inotropes may also be indicated in select patients. ,
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