Pulmonary edema

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Noncardiogenic pulmonary edema
)
Pulmonary edema
Other namesPulmonary oedema
critical care medicine pulmonology
SymptomsProgressive dyspnea, cough, fever, cyanosis, tachycardia
ComplicationsARDS, respiratory failure
CausesCardiogenic, Noncardiogenic (pneumonia, inhalation injury, sepsis, airway obstruction, high altitude)
Diagnostic methodMedical imaging, lab tests, ECG, echocardiography
TreatmentSupplemental oxygen, diuretics, treat underlying disease process

Pulmonary edema (

cardiogenic (caused by the heart) or noncardiogenic (all other types not caused by the heart).[2][3]

Various laboratory tests (

hypoxia.[7] The term edema is from the Greek οἴδημα (oidēma, "swelling"), from οἰδέω (oidéō, "(I) swell").[8][9]

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.[10] Due to the complication rate associated with pulmonary artery catheterization, other imaging modalities and diagnostic methods have become more popular.[11] 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 us 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).[12]

Cardiogenic

Cardiogenic pulmonary edema is typically caused by either volume overload or impaired left ventricular function. As a result, pulmonary pressures rises from the normal average of 15 mmHg.[13] As the pulmonary pressure rises, these pressures overwhelm the barriers and fluid enters the alveoli when the pressure is above 25 mmHg.[14] Depending whether the cause is acute or chronic determines how fast pulmonary edema develops and the severity of symptoms.[12] 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.[15]
  • 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.[16]
  • ischemic stroke.[17]

Flash Pulmonary Edema

A particularly severe type of cardiogenic pulmonary edema is flash pulmonary edema (FPE). Flash pulmonary edema is a clinical syndrome of acute heart failure that begins suddenly and accelerates rapidly. Frequently 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).

left ventricular filling pressures. Treatment of FPE should be directed at the underlying cause, but the mainstays are nitroglycerin, ensuring adequate oxygenation with non-invasive ventilation, and decrease of pulmonary circulation pressures while FPE stays.[20]

Recurrence of FPE is thought to be associated with hypertension[21] and may signify renal artery stenosis.[22] 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.

Direct Lung Injury

Acute lung injury
may cause pulmonary edema directly through injury to the vasculature and parenchyma of the lung, causes include:

  • Negative pressure pulmonary edema[27] is when inspiration is attempted against some sort of obstruction in the upper airway, most commonly happens as a result of laryngospasm in adults. This negative pressure in the chest ruptures capillaries and floods the alveoli with blood[28]
  • Pulmonary embolism[29]

Indirect Lung Injury

Special Causes

Some causes of pulmonary edema are less well characterized and arguably represent specific instances of the broader classifications above.

Signs and symptoms

Fluid within the alveoli (air spaces) of the lungs

The most common symptom of pulmonary edema is

excessive sweating, anxiety, and pale skin. Other signs include end-inspiratory crackles (crackling sounds heard at the end of a deep breath) on auscultation and the presence of a third heart sound.[3]

paroxysmal nocturnal dyspnea
(episodes of severe sudden breathlessness at night). These are common presenting symptoms of chronic and cardiogenic pulmonary edema due to left ventricular failure.

The development of pulmonary edema may be associated with symptoms and signs of "fluid overload" in the lungs; this is a non-specific term to describe the manifestations of right ventricular failure on the rest of the body. These symptoms may include peripheral edema (swelling of the legs, in general, of the "pitting" variety, wherein the skin is slow to return to normal when pressed upon due to fluid), raised jugular venous pressure and hepatomegaly, where the liver is excessively enlarged and may be tender or even pulsatile.

Additional symptoms such as fever, low blood pressure, injuries or burns may be present and can help characterize the cause and subsequent treatment strategies.

Diagnosis

Chest X-ray
of Pulmonary Edema with lines and overlay showing congestion

There is no single test for confirming that breathlessness is caused by pulmonary edema – there are many causes of shortness of breath; but there are methods to suggest a high probability of an edema.

Lab Tests

Low

B-type natriuretic peptide (BNP) is available in many hospitals, sometimes even as a point-of-care test. Low levels of BNP (<100 pg/ml) suggest a cardiac cause is unlikely, and suggest noncardiogenic pulmonary edema.[3]

Imaging Tests

Pulmonary edema on CT-scan (coronal MPR)

Chest X-ray has been used for many years to diagnose pulmonary edema due to its wide availability and relatively cheap cost.

hilum pattern, upper lobe diversion (biased blood flow to the superior parts instead of inferior parts of the lung), and possibly pleural effusions. In contrast, patchy alveolar infiltrates are more typically associated with noncardiogenic edema.[3]

Lung ultrasounds, employed by a healthcare provider at the point of care, is also a useful tool to diagnose pulmonary edema; not only is it accurate, but it may quantify the degree of lung water, track changes over time, and differentiate between cardiogenic and non-cardiogenic edema.[36] Lung ultrasound is recommended as the first-line method due to its wide availability, ability to be performed bedside, and wide diagnostic utility for other similar diseases.[4]

Especially in the case of cardiogenic pulmonary edema, urgent echocardiography may strengthen the diagnosis by demonstrating impaired left ventricular function, high central venous pressures and high pulmonary artery pressures leading to pulmonary edema.

Prevention

In those with underlying heart or lung disease, effective control of congestive and respiratory symptoms can help prevent pulmonary edema.[37]

Dexamethasone is in widespread use for the prevention of high altitude pulmonary edema. Sildenafil is used as a preventive treatment for altitude-induced pulmonary edema and pulmonary hypertension.[38][39] Sildenafil's mechanism of action is via phosphodiesterase inhibition which raises cGMP, resulting in pulmonary arterial vasodilation and inhibition of smooth muscle cell proliferation and indirectly fluid formation in the lungs.[40] While this effect has only recently been discovered, sildenafil is already becoming an accepted treatment for this condition, in particular in situations where the standard treatment of rapid descent (acclimatization) has been delayed for some reason.[41]

Management

The initial management of pulmonary edema, irrespective of the type or cause, is supporting vital functions while edema lasts.

Hypoxia may require supplementary oxygen to balance blood oxygen levels, but if this is insufficient then again mechanical ventilation may be required to prevent complications caused by hypoxia.[42] Therefore, if the level of consciousness is decreased it may be required to proceed to tracheal intubation and mechanical ventilation to prevent airway compromise. Treatment of the underlying cause is the next priority; pulmonary edema secondary to infection, for instance, would require the administration of appropriate antibiotics or antivirals.[2][3]

Cardiogenic pulmonary edema

Acute cardiogenic pulmonary edema often responds rapidly to medical treatment.

glyceryl trinitrate or ISDN) provided the blood pressure is adequate.[43]

bilevel positive airway pressure (CPAP/BiPAP) has been demonstrated to reduce mortality and the need of mechanical ventilation in people with severe cardiogenic pulmonary edema.[44]

It is possible for cardiogenic pulmonary edema to occur together with cardiogenic shock, in which the cardiac output is insufficient to sustain an adequate blood pressure to the lungs. This can be treated with inotropic agents or by intra-aortic balloon pump, but this is regarded as temporary treatment while the underlying cause is addressed and the lungs recover.[43]

Prognosis

As pulmonary edema has a wide variety of causes and presentations, the outcome or prognosis is often disease-dependent and more accurately described in relation to the associated syndrome. It is a major health problem, with one large review stating an incidence of 7.6% with an associated in hospital mortality rate of 11.9%.[2] Generally, pulmonary edema is associated with a poor prognosis with a 50% survival rate at one year, and 85% mortality at six years.[45]

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