Pulmonary edema (British English: oedema), also known as pulmonary congestion, is excessive fluid accumulation in the tissue or air spaces (usually alveoli) of the lungs. This leads to impaired gas exchange, most often leading to shortness of breath (dyspnea) which can progress to hypoxemia and respiratory failure. Pulmonary edema has multiple causes and is traditionally classified as cardiogenic (caused by the heart) or noncardiogenic (all other types not caused by the heart). Various laboratory tests (CBC, troponin, BNP, etc.) and imaging studies (chest x-ray, CT scan, ultrasound) are often used to diagnose and classify the cause of pulmonary edema. Treatment is focused on three aspects:
improving respiratory function, treating the underlying cause, and preventing further damage and allow full recovery to the lung. Pulmonary edema can cause permanent organ damage, and when sudden (acute), can lead to respiratory failure or cardiac arrest due to hypoxia. The term edema is from the Greek οἴδημα (oidēma, "swelling"), from οἰδέω (oidéō, "(I) swell").
Pathophysiology The amount of fluid in the lungs is governed by multiple forces and is visualized using the Starling equation. There are two hydrostatic pressures and two oncotic (protein) pressures that determine the fluid movement within the lung air spaces (alveoli). Of the forces that explain fluid movement, only the pulmonary wedge pressure is obtainable via pulmonary artery catheterization. Due to the complication rate associated with pulmonary artery catheterization, other imaging modalities and diagnostic methods have become more popular. Imbalance in any of these forces can cause fluid movement (or lack of movement) causing a buildup of fluid where it should not normally be. Although rarely clinically measured, these forces allow physicians to classify and subsequently treat the underlying cause of pulmonary edema.
Classification Pulmonary edema has a multitude of causes, and is typically classified as cardiogenic or noncardiogenic. Cardiogenic pulmonary edema is caused by increased hydrostatic pressure causing increased fluid in the pulmonary interstitium and alveoli. Noncardiogenic causes are associated with the oncotic pressure as discussed above causing malfunctioning barriers in the lungs (increased microvascular permeability).
Cardiogenic
Pulmonary Edema vs Congestive Heart Failure The term pulmonary edema literally means wet lungs. This term actually refers to a pathological condition of the lungs, frequently demonstrated by chest X-ray. Edema of the lungs should be thought of as the result of a disease such as congestive heart failure and not a disease in and of itself. In this case it would be a cardiac disease and not a pulmonary disease. Cardiogenic pulmonary edema is typically caused by either volume overload or impaired left ventricular function. As a result, pulmonary venous pressures rises from the normal average of 15 mmHg. As the pulmonary venous pressure rises, these pressures overwhelm the barriers and fluid enters the alveoli when the pressure is above 25 mmHg. Depending on whether the cause is acute or chronic determines how fast pulmonary edema develops and the severity of symptoms. Some of the common causes of cardiogenic pulmonary edema include:
Acute exacerbation of congestive heart failure which is due to the heart's inability to pump the blood out of the pulmonary circulation at a sufficient rate resulting in elevation in pulmonary wedge pressure and edema. Pericardial tamponade as well as treating pericardial tamponade via pericardiocentesis has shown to cause pulmonary edema as a result of increased left-sided heart strain. Heart Valve Dysfunction such as mitral valve regurgitation can cause increased pressure and energy on the left side of the heart (increased pulmonary wedge pressure) causing pulmonary edema. Hypertensive crisis can cause pulmonary edema as the elevation in blood pressure and increased afterload on the left ventricle hinders forward flow in blood vessels and causes the elevation in wedge pressure and subsequent pulmonary edema. In a recent systematic review, it was found that pulmonary edema was the second most common condition associated with hypertensive crisis after ischemic stroke.
Flash pulmonary edema Flash pulmonary edema is a clinical syndrome that begins suddenly and accelerates rapidly. Essentially all patients will present to the emergency department by ambulance. The initiating acute event often a vascular event such as intense vasoconstriction and not a cardiac event such as myocardial infarction. The most noticeable abnormality is edema of the lungs. Nevertheless it is a cardiovascular disease not a pulmonary disease. It is also known by other appellations including sympathetic crashing acute pulmonary edema (SCAPE). It is often associated with severe hypertension Typically, patients with the syndrome of flash pulmonary edema do not have chest pain are often not recognized as having a cardiovascular disease. Treatment of FPE should include reducing systemic vascular resistance with nitroglycerin, providing supplemental oxygenation, and decreasing left ventricular filling pressure. Effective treatment is evident by a decrease in dyspnea and normalization of vital signs. Important targets of therapy such as reduced systemic vascular resistance and reduced left atrial pressure are difficult if not impossible to monitor. Recurrence of FPE is thought to be associated with hypertension and may signify renal artery stenosis. Prevention of recurrence is based on managing or preventing hypertension, coronary artery disease, renovascular hypertension, and heart failure.
Noncardiogenic Noncardiogenic pulmonary edema is caused by increased microvascular permeability (increased oncotic pressure) leading to increased fluid transfer into the alveolar spaces. The pulmonary artery wedge pressure is typically normal as opposed to cardiogenic pulmonary edema where the elevated pressure is causing the fluid transfer. There are multiple causes of noncardiogenic edema with multiple subtypes within each cause. Acute respiratory distress syndrome (ARDS) is a type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Although ARDS can present with pulmonary edema (fluid accumulation), it is a distinct clinical syndrome that is not synonymous with pulmonary edema.
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