ACUTE PULMONARY EDEMA

Diagnosis of Pulmonary Edema

• Patients with severe trauma or infection may develop noncardiogenic pulmonary edema due to fluid resuscitation increasing lung vascular hydrostatic pressure.
• Cardiogenic pulmonary edema is often indicated by abnormal cardiac examination, including the presence of an S3 gallop, which has high specificity but low sensitivity.
• Other findings on examination for cardiogenic edema include murmurs consistent with valvular stenosis or regurgitation, elevated neck veins, an enlarged and tender liver, and peripheral edema.
• The lung examination is not helpful in differentiating the type of edema, as alveolar flooding from any cause will manifest as inspiratory crackles and often rhonchi.
• Electrocardiographic findings and elevated troponin levels may suggest myocardial ischemia or infarction, but elevated troponin levels can also occur in severe sepsis.
• Laboratory testing for pulmonary edema includes measurement of electrolytes, serum osmolarity, toxicology screen, serum amylase and lipase levels, and plasma levels of brain natriuretic peptide (BNP).
• BNP levels are often used in the evaluation of pulmonary edema, with levels below 100 pg per milliliter indicating heart failure is unlikely and levels above 500 pg per milliliter indicating heart failure is likely.
• However, BNP levels between 100 and 500 pg per milliliter provide inadequate diagnostic discrimination, and caution is needed in interpreting BNP levels in critically ill patients.
• BNP levels can be elevated in critically ill patients even in the absence of heart failure, and levels between 100 and 500 pg per milliliter are common in these patients.
• BNP levels must be interpreted with caution in critically ill patients, as they may not reliably indicate heart failure in this group.
• Physiology of microvascular fluid exchange in the lung involves continuous movement of fluid from the vascular to the interstitial space, and increased hydrostatic pressure in the microcirculation leads to increased transvascular fluid filtration.
• The removal of edema fluid from the air spaces of the lung depends on active transport of sodium and chloride across the alveolar epithelial barrier.

Distinguishing Cardiogenic from Noncardiogenic Pulmonary Edema

• Radiographic features that may help differentiate cardiogenic from noncardiogenic pulmonary edema include heart size, width of the vascular pedicle, vascular distribution, distribution of edema, pleural effusions, peribronchial cuffing, septal lines, and air bronchograms
• Transthoracic echocardiogram may not always be sufficiently informative and is less sensitive in identifying diastolic dysfunction
• Newer echocardiographic techniques such as tissue Doppler imaging of the mitral-valve annulus may be used to determine left ventricular end-diastolic pressure and to assess diastolic dysfunction
• Pulmonary-artery catheterization is considered the gold standard for determining the cause of acute pulmonary edema and permits monitoring of cardiac filling pressures, cardiac output, and systemic vascular resistance during treatment
• Elevated pulmonary-artery occlusion pressure above 18 mm Hg indicates cardiogenic pulmonary edema or pulmonary edema due to volume overload
• Complications of pulmonary-artery catheterization include hematoma at the insertion site, arterial puncture, bleeding, arrhythmias, and bloodstream infection
• The algorithm for the diagnostic approach to the patient with pulmonary edema is based on clinical experience and data regarding the value of various clinical and laboratory findings for distinguishing the cause of pulmonary edema
• Noninvasive approaches for diagnosis may lead to misclassification of some patients, requiring repeated and ongoing assessment
• The stepwise algorithm for the clinical differentiation between cardiogenic and noncardiogenic pulmonary edema involves a transthoracic echocardiogram or transesophageal echocardiogram, and pulmonary-artery catheterization
• Care for the critically ill patient is a dynamic process, often requiring simultaneous diagnosis and treatment
• Some treatments may be initiated empirically before testing, such as diuretic therapy for suspected cardiogenic edema
• Approximately 10 percent of patients with acute pulmonary edema have multiple causes of edema, for example, a patient with septic shock and acute lung injury may have volume overload due to aggressive fluid resuscitation or myocardial dysfunction