Noncardiogenic pulmonary edema

INTRODUCTION — Pulmonary edema is due to the movement of excess fluid into the alveoli as a result of an alteration in one or more of Starling's forces. In cardiogenic pulmonary edema, a high pulmonary capillary pressure (as estimated clinically from the pulmonary artery wedge pressure) is responsible for the abnormal fluid movement [1,2]. (See "Pathophysiology of cardiogenic pulmonary edema" and "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

In contrast, noncardiogenic pulmonary edema is caused by various disorders in which factors other than elevated pulmonary capillary pressure are responsible for protein and fluid accumulation in the alveoli [3]. The distinction between cardiogenic and noncardiogenic causes is not always possible, since the clinical syndrome may represent a combination of several different disorders. The diagnosis is important, however, because treatment varies considerably depending upon the underlying pathophysiologic mechanisms.

THE STARLING RELATIONSHIP — Fluid balance between the interstitium and vascular bed in the lung, as in other microcirculations, is determined by the Starling relationship, which predicts the net flow of liquid across a membrane. This can be expressed in the following equation:

where:

●Lp is the unit permeability (or porosity) of the capillary wall.

●S is the surface area available for fluid movement.

●Pcap and Pif are the capillary and interstitial fluid hydraulic pressures.

●πcap and πif are the capillary and interstitial fluid oncotic pressures; the interstitial oncotic pressure is derived primarily from filtered plasma proteins and to a lesser degree from proteoglycans in the interstitium.

●s represents the reflection coefficient of proteins across the capillary wall (with values ranging from 0 if completely permeable to 1 if completely impermeable).

In normal microvessels, there is ongoing filtration of a small amount of low protein liquid. In noncardiogenic pulmonary edema, the most common mechanism for a rise in transcapillary filtration is an increase in capillary permeability. At a given increase in capillary permeability, the rate of accumulation of lung liquid is related in part to the functional capacity of the lymphatic vessels to remove the excess fluid.

DEFINITION OF NONCARDIOGENIC PULMONARY EDEMA — Noncardiogenic pulmonary edema is identified clinically by the presence of radiographic evidence of alveolar fluid accumulation without hemodynamic evidence to suggest a cardiogenic etiology (ie, pulmonary artery wedge pressure ≤18 mmHg). The accumulation of fluid and protein in the alveolar space leads to decreased diffusing capacity, hypoxemia, and shortness of breath.

The major causes of noncardiogenic pulmonary edema are the acute respiratory distress syndrome (ARDS) [2] and, less often, high altitude and neurogenic pulmonary edema. Other less common causes include pulmonary edema due to opioid overdose, pulmonary embolism, eclampsia, transfusion-related acute lung injury and acute kidney injury (sometimes referred to as “uremic lung”) [4]. Hypoalbuminemia alone is not a cause of pulmonary edema. (See 'Absence of pulmonary edema with hypoalbuminemia' below.)

PERMEABILITY PULMONARY EDEMA DUE TO ARDS — The alveolar-capillary membrane becomes damaged and leaky in cases of permeability pulmonary edema, allowing increased movement of water and proteins from the intravascular space to the interstitial space. In most patients, the concentration of protein in the interstitium exceeds 60 percent of the plasma value, compared to less than 45 percent in cardiogenic pulmonary edema [5].

Permeability pulmonary edema is the most prominent feature of acute respiratory distress syndrome (ARDS) [6]. In the past, many authors equated the clinical disorder ARDS with the pathological entity of permeability pulmonary edema. However, these two terms should not be used interchangeably. Although some degree of permeability edema is invariably present at the onset of ARDS, other important structural abnormalities of the lung typically emerge as ARDS evolves. Furthermore, many episodes of permeability pulmonary edema never result in the severe physiological impairment that is required for the designation ARDS. (See "Acute respiratory distress syndrome: Clinical features, diagnosis, and complications in adults".)

ARDS can be seen in a number of disorders, including sepsis, acute pulmonary infection, non-thoracic trauma, inhaled toxins, disseminated intravascular coagulation, shock lung, freebase cocaine smoking, postcoronary artery bypass grafting (especially in patients on amiodarone), inhalation of high oxygen concentrations, and acute radiation pneumonitis. Regardless of etiology, the clinical scenario is similar in most patients once membrane damage has occurred. Sepsis- or ischemia-induced release of cytokines, such as interleukin-1, interleukin-8, and tumor necrosis factor, may play an important role in the increase in pulmonary capillary permeability, at least in part via the recruitment of neutrophils [7]. (See "Acute respiratory distress syndrome: Epidemiology, pathophysiology, pathology, and etiology in adults".)

Presentation and diagnosis — Patients with ARDS present with severe respiratory distress (dyspnea) in association with the acute appearance of diffuse chest radiographic infiltrates and hypoxemia. The onset of ARDS is often within the first two hours after an inciting event, although this can be delayed as long as one to three days. Chest radiographs usually progress to a bilateral alveolar filling pattern. The diagnosis of permeability pulmonary edema requires distinction from cardiogenic pulmonary edema and from other causes of lung disease or injury.

Patients with noncardiogenic (or cardiogenic) pulmonary edema rarely have unilateral edema [8-10]. Unilateral noncardiogenic pulmonary edema may be caused by conditions ipsilateral to the edema such as aspiration, contusion, re-expansion, and pulmonary vein occlusion (eg, veno-occlusive disease or extrinsic compression) and by conditions contralateral to the edema such as pulmonary embolism and lobectomy [8]. These lesions should be distinguished from unilateral cardiogenic pulmonary edema, which is chiefly caused by eccentric mitral regurgitation [11] or following minimally invasive cardiac surgery [12].

Distinction from heart failure — Clinically and radiographically, ARDS closely resembles severe cardiogenic pulmonary edema. The distinction between these disorders is often apparent from the clinical circumstances at the onset of respiratory distress. As examples, pulmonary edema occurring in the setting of an acute coronary syndrome is almost always cardiogenic, while that occurring in the setting of sepsis strongly suggests a noncardiac etiology. Pulmonary edema occurring in the setting of multiple transfusions could be due to a combination of cardiogenic pulmonary edema (eg, due to volume) and acute lung injury. (See "Clinical manifestations and diagnosis of cardiogenic shock in acute myocardial infarction" and "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

●Pulmonary artery catheter – A pulmonary artery (or Swan-Ganz) catheter should be placed if the mechanism of edema formation cannot be discerned with confidence. A pulmonary artery wedge pressure less than 18 mmHg favors acute lung injury over cardiogenic pulmonary edema. (See "Pulmonary artery catheterization: Indications, contraindications, and complications in adults".)

It is important to appreciate that pulmonary artery catheterization can be misleading in certain settings. Most important, myocardial ischemia can cause severe but transient left ventricular dysfunction, leading to "flash" pulmonary edema. If the wedge pressure is first measured after the ischemia has resolved (and left ventricular function has improved), a relatively normal value may be obtained, leading to the erroneous conclusion that the respiratory distress was caused by acute lung injury. (See "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

On the other hand, an elevated pulmonary artery wedge pressure does not exclude the possibility of acute lung injury. It is estimated that as many as 20 percent of patients with ARDS have concomitant left ventricular dysfunction [7], and the percentages are much higher in patients with ARDS secondary to sepsis [13]. Right ventricular dilation is also commonly present in ARDS, while right ventricular dysfunction may be present in the most severe cases and predict worse outcomes [14]. The diagnosis of acute lung injury cannot be made easily when the wedge pressure is elevated; thus, the clinical course must be observed as the wedge pressure responds to treatment. If pulmonary infiltrates and hypoxemia do not improve appreciably within 24 to 48 hours after fluid restriction (with or without diuresis) and normalization of the wedge pressure, then acute lung injury probably coexists with cardiogenic edema.

●Plasma BNP – Measurement of plasma B-type natriuretic peptide (BNP), or N-terminal pro-BNP, has been used to distinguish heart failure (high BNP) from lung disease (normal or mildly elevated BNP) as a cause of dyspnea with a high degree of accuracy even in patients with both lung and heart disease [15]. However, intermediate values are often not helpful. The role of these biomarkers in the diagnosis of pulmonary edema has been less well studied. Data in the ICU setting suggested limited ability to discriminate ARDS from cardiogenic pulmonary edema [16], as levels may increase with the development [17]and severity [18] of ARDS. (See "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

Clinical prediction tools have been developed to distinguish acute lung injury from cardiogenic pulmonary edema [19]. These may provide a guide to expediting initial therapy, but require further prospective evaluation. A number of novel biomarkers have also been proposed to aid in this distinction [20].

Other lung diseases — Two pulmonary disorders are sometimes confused with ARDS: diffuse alveolar hemorrhage and cancer.

●Diffuse alveolar hemorrhage, often due to a pulmonary capillaritis or diffuse alveolar damage, should be considered whenever respiratory distress develops in association with a large, otherwise unexplained drop in the blood hemoglobin concentration. Hemoptysis may be minimal or absent prior to intubation; however, bronchoscopy after intubation invariably reveals bloody secretions throughout the airways during active hemorrhage.

Bland alveolar hemorrhage, which is characterized by hemorrhage into the alveolar spaces without inflammation or destruction of the alveolar structures, may be caused by elevated LV end diastolic pressure, coagulopathy, and, rarely, anticoagulant or antiplatelet therapy. (See "The diffuse alveolar hemorrhage syndromes".)

●Cancer sometimes disseminates throughout the lungs so rapidly that the ensuing respiratory failure may be mistaken for ARDS. This is most often due to lymphoma or acute leukemia [21], but lymphangitic spread of solid tumors, acute toxicity from chemotherapy (eg, mitomycin [also known as Mitomycin-C], methotrexate), and cancer-associated DIC occasionally behave in a similar fashion [22]. Newer cancer treatments, including immune checkpoint inhibitors, have also been associated with pneumonitis [23]. (See "Toxicities associated with immune checkpoint inhibitors".)

Treatment — There are currently no known measures to correct the permeability abnormality in ARDS. Clinical management involves treatment of the underlying disease (eg, antibiotics for infection) and supportive measures to maintain cellular and metabolic function, while waiting for the acute lung injury to resolve. These supportive measures include mechanical ventilation, maintenance of adequate nutrition, and hemodynamic monitoring when necessary to guide fluid management and cardiovascular support [24]. Patients with severe ARDS may require extracorporeal membrane oxygenation in addition to supportive medical therapies [25]. (See "Acute respiratory distress syndrome: Ventilator management strategies for adults" and "Acute respiratory distress syndrome: Fluid management, pharmacotherapy, and supportive care in adults" and "Evaluation and management of suspected sepsis and septic shock in adults".)

Lowering the pulmonary artery wedge pressure with diuretics and fluid restriction can improve pulmonary function and perhaps outcome [26,27]. One study, for example, analyzed survival and length of stay in the intensive care unit for 40 patients with ARDS [26]. The patients were divided into two groups: those with a reduction in pulmonary capillary wedge pressure (PCWP) of at least 25 percent; and those with less or no reduction in PCWP. Survival was greater in the patients with a large fall in PCWP (75 versus 29 percent). This difference remained statistically significant after stratifying patients by age and by the APACHE II severity of illness index. In a later study in which 1000 patients with acute lung injury were randomized to a conservative versus liberal fluid management strategy, the conservative strategy improved oxygenation and shortened duration of mechanical ventilation and ICU stay, but did not reduce the incidence of shock, use of dialysis or mortality during the first 60 days [28]. (See "Predictive scoring systems in the intensive care unit".)

A number of pharmacologic therapies for ARDS have been evaluated [29]. These include inhaled vasodilators (nitric oxide, prostacyclin), anti-inflammatory therapies (glucocorticoids, statins [30], prostaglandin E1), antioxidants (dietary oil supplementation), and exogenous surfactant. Novel mechanical ventilation strategies, including high-frequency ventilation, liquid ventilation, and prone positioning [31], as well as preventive strategies (eg, aspirin) [32] have also been investigated. At present, NONE has shown consistent and unequivocal clinical benefit [33]. Preclinical and early clinical data suggest that human mesenchymal stem cells may attenuate lung injury and promote tissue repair in ARDS. (See "Acute respiratory distress syndrome: Investigational or ineffective therapies in adults".)

Prognosis — The outcome of patients with ARDS has improved over time; hospital mortality was approximately 60 percent in the years 1967 to 1981 and declined to 30 to 40 percent in the 1990s. As an example of this trend, one study evaluated 918 patients with ARDS at a single institution between 1983 and 1993 [34]. The mortality from sepsis-related ARDS declined from 67 percent in 1990 to 40 percent in 1993; the improvement was largely confined to patients under age 60. In a systematic analysis of ARDS studies published between 1994 and 2006, a decline in overall mortality rates of 1.1 percent per year was demonstrated [35]. The enhanced survival is probably related to a variety of improvements in supportive care. Despite these encouraging data, ARDS remains a world-wide problem with high mortality that is both under recognized and undertreated [36].

Most deaths are due to the severity of the underlying disease, particularly multiorgan failure, rather than the respiratory disease. While early deaths are typically due to the underlying cause of the ARDS, later deaths often result from nosocomial pneumonia and sepsis. Long-term survivors of ARDS typically show only mild abnormalities in pulmonary function and are usually asymptomatic, although long-term physical, cognitive, and psychological sequelae have been described [37,38]. (See "Acute respiratory distress syndrome: Prognosis and outcomes in adults".)

OTHER NONCARDIOGENIC FORMS OF PULMONARY EDEMA — Other more unusual types of noncardiogenic pulmonary edema, often with unclear pathophysiology, have been described.

High altitude pulmonary edema — High-altitude pulmonary edema (HAPE), which generally occurs among individuals who rapidly ascend to altitudes above 12,000 to 13,000 feet (3600 to 3900 m), accounts for a majority of deaths due to high altitude disease [39,40]. An abnormally pronounced degree of hypoxic pulmonary vasoconstriction at a given altitude appears to underlie the pathogenesis of this disorder [14]. (See "High-altitude illness: Physiology, risk factors, and general prevention" and "High-altitude pulmonary edema".)

Neurogenic pulmonary edema — Neurogenic pulmonary edema occurs after a variety of neurologic disorders and procedures, including head injury, intracranial surgery, grand mal seizures, subarachnoid or intracerebral hemorrhage, and electroconvulsive therapy [41]. Sympathetic overreactivity, with massive catecholamine surges, shifts blood from the systemic to the pulmonary circulation with secondary elevations of left atrial and pulmonary capillary pressures [42]. Pulmonary capillary leak caused by pressure-induced mechanical injury and/or direct nervous system control over capillary permeability may play a contributory role. The clinical presentation is characterized by acute hypoxemia, tachypnea, tachycardia, diffuse rales, and frothy sputum or hemoptysis. Symptom onset tends to be rapid and most cases resolve within 48 to 72 hours. The outcome is determined by the course of the primary neurologic insult. It is important to distinguish neurogenic pulmonary edema from cardiogenic pulmonary edema in the setting of stress cardiomyopathy. (See "Neurogenic pulmonary edema" and "Clinical manifestations and diagnosis of stress (takotsubo) cardiomyopathy".)

Reperfusion pulmonary edema — Reperfusion pulmonary edema appears to represent a form of high-permeability lung injury that is limited to those areas of lung from which proximal thromboembolic obstructions have been removed. It may appear up to 72 hours after surgery and is highly variable in severity, ranging from a mild form of edema resulting in postoperative hypoxemia to an acute, hemorrhagic and fatal complication [43-45]. At experienced centers, venovenous extracorporeal life support has been used as a bridge to recovery or transplant when all other conventional strategies have failed [46,47] (see "Chronic thromboembolic pulmonary hypertension: Pulmonary thromboendarterectomy"). A similar condition may occur following lung transplantation due to ischemia-reperfusion injury. (See "Primary lung graft dysfunction".)

Re-expansion pulmonary edema — Re-expansion pulmonary edema (RPE) usually occurs unilaterally after rapid re-expansion of a collapsed lung (typically for greater than three days) in patients with a pneumothorax [48], with rates ranging from 16 to 33 percent. Risk factors include diabetes, size of pneumothorax, and presence of pleural effusion [49,50]. It may rarely follow evacuation of large volumes of pleural fluid (>1 to 1.5 liters) (<1 percent) [51-54] or removal of an obstructing endobronchial tumor.

The pathophysiologic mechanism is unknown. Proposed mechanisms include direct injury from surfactant dysfunction in chronic atelectatic lung, increased transpleural pressures when excessively negative pleural pressures are created during fluid or air removal in the setting of an unexpandable lung, or indirect injury from reperfusion.

RPE appears to be related to the rapidity of lung re-expansion and to the severity and duration of lung collapse. However, a study examining development of re-expansion pulmonary edema following thoracentesis found that it was independent of the volume of fluid removed and pleural pressures, and recommended that even large pleural effusions be drained completely as long as chest pain or end-expiratory pleural pressure less than -20 cm H₂O does not develop [53].

Patients typically present soon (minutes to hours) after the inciting event, although presentation can be delayed for up to 24 to 48 hours in some cases. The clinical course varies from isolated radiographic changes to complete cardiopulmonary collapse but most patients present with acute onset dyspnea, cough and hypoxemia. Typical CT findings include ipsilateral ground-glass opacities, septal thickening, focal consolidation, and areas of atelectasis [55].

A mortality rate as high as 20 percent has been described in one small review [56]; however consistent with our experience, the mortality is much lower with later and larger series reporting a mortality rate less than 5 percent [52,53,57].

Treatment is supportive, mainly consisting of supplemental oxygen and, if necessary, mechanical ventilation. The disease is usually self-limited.

Opioid overdose — First described by Osler in 1880 [58], pulmonary edema can sometimes complicate an overdose of heroin or methadone [59]; other related agents, including fentanyl and naloxone, have also been implicated [60]. Risk factors include male sex and shorter duration of heroin use. Most cases occur immediately or within hours of drug injection. The chest radiograph usually demonstrates a nonuniform distribution of pulmonary edema.

The pathophysiology of this form of pulmonary edema is unknown; a combination of direct toxicity of the drug, hypoxia, and acidosis secondary to hypoventilation and/or cerebral edema has been proposed [61,62]. The observation that edema fluid contains protein concentrations nearly identical to plasma and that pulmonary artery wedge pressures, when measured, are normal suggests an alveolar-capillary membrane leak as the initiating cause. Resolution of this form of pulmonary edema is rapid once hypoventilation and hypoxia are reversed by the institution of assisted ventilation. In one case series, 9 of 27 patients (33 percent) required mechanical ventilation; all but one were extubated within 24 hours [63]. Supportive care also includes use of naloxone to reverse the opioid effects. The alarming increase in opioid use and dependency suggests that clinicians will see more cases of pulmonary edema related to opioid overdose in the emergency room and intensive care unit [64,65].

Salicylate toxicity — Aspirin is one of many drugs occasionally associated with the development of noncardiogenic pulmonary edema. Salicylate-induced noncardiogenic pulmonary edema and acute lung injury (ALI) generally occur in older patients with chronic salicylate intoxication [66,67], but should be considered in all patients following aspirin overdose. The medical history is critical to making the diagnosis, as misdiagnosis or delayed diagnosis can lead to a significant increase in morbidity and mortality [67]. Salicylate-induced ALI and pulmonary edema can complicate volume resuscitation and administration of sodium bicarbonate, two mainstays of treatment in this setting. Thus, the presence of salicylate-induced pulmonary edema is considered an absolute indication for hemodialysis [68]. (See "Salicylate (aspirin) poisoning: Clinical manifestations and evaluation".)

Other exogenous agents — Several commonly-prescribed medications have been associated with noncardiogenic pulmonary edema, including amiodarone, bortezomib, and immunosuppressive agents (eg, sirolimus, everolimus) [69,70]. It may be difficult to distinguish noncardiogenic pulmonary edema from heart failure in cardiac patients or infection in immunosuppressed patients. Additional objective data, including invasive hemodynamics and tissue biopsy, may be helpful in these cases. Acute lung injury and death have also been reported with use of electronic cigarettes (vaping), and direct injury to lung epithelial cells with capillary leak has been proposed as a mechanism. (See "E-cigarette or vaping product use-associated lung injury (EVALI)" and "Vaping and e-cigarettes".)

Pulmonary embolism — Acute pulmonary edema in association with a massive pulmonary embolus (PE) or multiple smaller emboli is uncommon but well described [71,72]. PE can cause pulmonary edema by injuring the pulmonary and adjacent pleural systemic circulations, elevating hydrostatic pressures in pulmonary and/or systemic veins, and perhaps by lowering pleural pressure due to atelectasis. PE may also decrease the exit rates of pleural fluid by increasing the systemic venous pressure (thereby hindering lymphatic drainage) or possibly by decreasing pleural pressure (thereby hindering lymphatic filling). The effusions are typically small and unilateral, and may become loculated if the diagnosis is delayed [73]. Older studies showed that 20 percent of PE-related effusions are transudates, suggesting that hydrostatic changes can also be important [74]. However, in a later case series, 26 of 93 patients with effusions following PE underwent thoracentesis and all of the fluids met Light's criteria for exudate (see "Pleural fluid analysis in adults with a pleural effusion"), suggesting a primary role for vascular injury [75].

Viral infections — Rapidly progressive noncardiogenic pulmonary edema associated with profound hypotension and a high case fatality rate has been described with hantavirus infection (see "Hantavirus cardiopulmonary syndrome") [76], dengue hemorrhagic fever/dengue shock syndrome (see "Dengue virus infection: Clinical manifestations and diagnosis"), and most recently with COVID-19 infection (see "COVID-19: Clinical features"). Enteroviral 71 infection in young children [77] and SARS coronavirus infection in adults [78] are other causes of viral-induced noncardiogenic pulmonary edema and hemorrhage (see "Severe acute respiratory syndrome (SARS)"). The strain of H1N1 influenza A that caused the 2009 to 2010 pandemic caused severe ARDS in some patients (see "Seasonal influenza in adults: Clinical manifestations and diagnosis"). There have also been reports of vascular leakage and respiratory failure in the setting of severe Ebola virus disease [79].

Pulmonary veno-occlusive disease — Pulmonary veno-occlusive disease is a cause of pulmonary hypertension and noncardiogenic pulmonary edema. This condition is discussed in detail separately. (See "Epidemiology, pathogenesis, clinical evaluation, and diagnosis of pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis in adults".)

Transfusion-related acute lung injury — Transfusion-related acute lung injury (TRALI) is a rare but potentially fatal complication of blood product transfusion that involves neutrophil activation and pulmonary edema. Further details are provided separately. (See "Transfusion-related acute lung injury (TRALI)".)

ABSENCE OF PULMONARY EDEMA WITH HYPOALBUMINEMIA — In older patients with heart failure with preserved ejection fraction, hypoalbuminemia due to age, malnutrition, or sepsis may lower colloid osmotic pressure and facilitate the onset of pulmonary edema [80]. In patients with acute heart failure, hypoalbuminemia has also been associated with pleural effusions [81], and is an independent predictor of in-hospital and post-discharge mortality [82]. In a study of more than 7000 patients with acute coronary syndrome, serum albumin level ≤3.50 g/dL was an independent predictor of new-onset heart failure and in-hospital mortality [83].

Although hypoalbuminemia can lead to peripheral edema by lowering the transcapillary oncotic pressure gradient, it does not generally produce pulmonary edema. The pulmonary capillaries appear to have a greater baseline permeability to albumin and therefore have a higher interstitial oncotic pressure (about 18 mmHg) than do peripheral capillaries [84]. A fall in the plasma albumin concentration is associated with a parallel decline in the pulmonary interstitial oncotic pressure. The net effect is little or no change in the transcapillary oncotic pressure gradient and therefore no pulmonary edema, unless there is a concurrent rise in left atrial and pulmonary capillary pressures. (See "Pathophysiology and etiology of edema in adults", section on 'Compensatory factors'.)

SUMMARY

●Overview – Noncardiogenic pulmonary edema is caused by various disorders in which factors other than elevated pulmonary capillary pressure are responsible for protein and fluid accumulation in the alveoli. In contrast, a high pulmonary capillary pressure is responsible for the abnormal fluid movement in cardiogenic pulmonary edema. Noncardiogenic pulmonary edema may be difficult to distinguish from cardiogenic pulmonary edema and a mixed picture can occur. (See 'Introduction' above.)

●Pathogenesis – Fluid balance between the interstitium and vascular bed in the lung, as in other microcirculations, is determined by the Starling relationship, which predicts the net flow of liquid across a membrane. In noncardiogenic pulmonary edema, the most common mechanism for a rise in transcapillary filtration is an increase in capillary permeability. Hypoalbuminemia alone is not a cause of pulmonary edema but can contribute to pleural effusions and increased mortality in patients with acute heart failure as well as in those with acute coronary syndrome. (See 'The Starling relationship' above and 'Absence of pulmonary edema with hypoalbuminemia' above.)

●Definition – Noncardiogenic pulmonary edema is identified clinically by the presence of radiographic evidence of alveolar fluid accumulation without hemodynamic evidence to suggest a cardiogenic etiology (ie, pulmonary artery wedge pressure ≤18 mmHg). (See 'Definition of noncardiogenic pulmonary edema' above.)

●Etiologies

•The most common cause of noncardiogenic pulmonary edema is acute respiratory distress syndrome. (See 'Permeability pulmonary edema due to ARDS' above.)

•Less common causes are high altitude and neurogenic pulmonary edema. (See 'High altitude pulmonary edema' above and 'Neurogenic pulmonary edema' above.)

•Others include reperfusion and re-expansion pulmonary edema, heroin overdose or use of vaping products, and salicylate or other drug toxicity. (See 'Reperfusion pulmonary edema' above and 'Re-expansion pulmonary edema' above and 'Opioid overdose' above and 'Salicylate toxicity' above and 'Other exogenous agents' above.)

•Other less common causes include pulmonary edema due to pulmonary embolism and eclampsia, viral infections, pulmonary veno-occlusive disease, and transfusion-related acute lung injury. (See 'Pulmonary embolism' above and 'Viral infections' above and 'Pulmonary veno-occlusive disease' above and 'Transfusion-related acute lung injury' above.)