Pulmonary Edema (cont.)
How is pulmonary edema diagnosed?
Pulmonary edema is typically diagnosed by a chest X-ray.
A normal chest radiograph (X-ray) consists of a central white area pertaining to the heart and
its main blood vessels plus the bones of the vertebral column, with the lung
fields showing as darker fields on either side, enclosed by the bony structures
of the chest wall.
A typical chest X-ray with pulmonary edema may show a more white appearance
over both lung fields than usual. More severe cases of pulmonary edema can
demonstrate significant opacification (whitening) over the lungs with minimal
visualization of the normal lung fields. This whitening represents filling of
the alveoli as a result of pulmonary edema, but it may give minimal information
about the possible underlying cause.
To identify the cause of pulmonary edema, a thorough
assessment of the patient's clinical picture is essential. A careful medical history and physical
examination often provide invaluable information regarding the cause.
Other diagnostics tools used in assessing the underlying cause of pulmonary
edema include the measurement of plasma B-type natriuretic peptide (BNP) or
N-terminal pro-BNP. This is a protein marker (a hormone) that
will rise in the blood due to the stretch of the chambers of the heart.
Elevation of the BNP nanogram (one billionth of a gram) per liter greater than a
few hundred (300 or more) is highly suggestive of cardiac pulmonary edema. On the other hand, values
less than 100 essentially rule out heart failure as the cause.
More invasive methods are occasionally necessary to distinguish between
cardiac and noncardiac pulmonary edema in more complicated and critical
situations. A pulmonary artery catheter (Swan-Ganz) is a thin, long tube
(catheter) inserted into
the large veins of the chest or the neck and advanced through the right-sided
chambers of the heart and lodged into the pulmonary capillaries (small branches of the blood vessels of the lungs). This device has
the capability of directly measuring the pressure in the pulmonary vessels,
called the pulmonary artery wedge pressure.
- A wedge pressure of 18 mmHg or
higher is consistent with cardiogenic pulmonary edema,
- whereas a wedge pressure
of less than 18 mmHg usually favors a non-cardiogenic cause of pulmonary edema.
A Swan-Ganz catheter placement and data interpretation is done only in the
intensive care unit
(ICU) setting.
Next: What is the treatment for pulmonary edema? »
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