Pulmonary edema
Pulmonary edema | |
---|---|
Other names | Pulmonary oedema |
critical care medicine pulmonology | |
Symptoms | Progressive dyspnea, cough, fever, cyanosis, tachycardia |
Complications | ARDS, respiratory failure |
Causes | Cardiogenic, Noncardiogenic (pneumonia, inhalation injury, sepsis, airway obstruction, high altitude) |
Diagnostic method | Medical imaging, lab tests, ECG, echocardiography |
Treatment | Supplemental oxygen, diuretics, treat underlying disease process |
Pulmonary edema (
Various laboratory tests (
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).
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
- Inhalation of hot or toxic gases[12] (including vaping-associated lung injury)
- high-energy trauma(e.g. vehicle accidents)
- Aspiration, e.g., gastric fluid
- Reexpansion, i.e. post large volume thoracocentesis, resolution of pneumothorax, post decortication, removal of endobronchial obstruction, effectively a form of negative pressure pulmonary oedema.
- Reperfusion injury, i.e., postpulmonary thromboendartectomy or lung transplantation
- Transfusion associated Acute Lung Injury is a specific type of blood-product transfusion injury that occurs when the donors plasma contained antibodies against the recipient, such as anti-HLA or anti-neutrophil antibodies.[26]
- 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
- Neurogenic causesstrangulation, electrocution).
- Transfusion Associated Circulatory Overload occurs when multiple blood transfusions or blood-products (plasma, platelets, etc.) are transfused over a short period of time.[31]
- It includes acute lung injury and adult respiratory distress syndrome
- Pancreatitis
Special Causes
Some causes of pulmonary edema are less well characterized and arguably represent specific instances of the broader classifications above.
- Arteriovenous malformation
- Hantaviruspulmonary syndrome
- Atrax robustus[35]
Signs and symptoms
The most common symptom of pulmonary edema is
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
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
Imaging Tests
Chest X-ray has been used for many years to diagnose pulmonary edema due to its wide availability and relatively cheap cost.
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.
Cardiogenic pulmonary edema
Acute cardiogenic pulmonary edema often responds rapidly to medical treatment.
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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