Pulmonary Edema

Abnormal accumulation of fluid in the extravascular spaces and tissues of the lung

• 1. Interstitial edema
• 2. Alveolar edema

• Pathology: 
• -Perivascular cuff of edema around pulmonary vessels: 
• 

• -Septal lines on CXR: horizontal white lines, perpendicular to the pleura:
• 

No impairment of lung function with interstitial edema

• Alveolar edema:
• -Fluid in the alveolar space
• -CXR demonstrates (usually) bilateral, symmetric opacity that is most often worse at the base of the lungs:
• 

"butterfly" or "bat" wing appearance

Starling equation: movement of fluid across a membrane

• NET FLUID OUT = K [ (Pc-Pi) -σ(πc-πi)]
• -hydrostatic pressures
• -osmotic pressures

-Continuous loss of fluid out of the capillaries into the interstitial space, eventually leaves via the lymphatics. 

• Pathogenesis:
• 1. Increase in capillary hydrostatic pressure [Pc]
• (Increase in alveolar pressure causes compensatory increase in lymph flow)
• - myocardial infarction
• - hypertensive left ventricular failure
• - mitral stenosis
• - mitral stenosis
• - transfusion overload
• - pulmonary veno-occlusive disease

• 2. Increase capillary permeability [K, σ, πi]
• - inhaled or circulating toxins 
• - adult respiratory distress syndrome
• - radiation
• - oxygen toxicity
• edema fluid has high protein concentration
• 3. Decrease in interstitial hydrostatic pressure [Pi]
• (common cause of unilateral pulmonary edema)
• - rapid removal of pleural effusion or   pneumothorax
• - rapid re-expansion of collapsed lung
• - hyperinflation of lung

• 4. Decrease colloid osmotic pressure [πc]
• - Saline oversaturation
• - Hypoproteinemia

• 5. Lymphoid insufficiency
• - silicosis (rare - from sand blasting)
• - lymphangitis carcinomatosa
• - lung transplantation (loss of lymphatics)

• 6. Uncertain etiology
• - high-altitude pulmonary edema (HAPE)
• 1. Strong association with high pulmonary artery pressure but normal wedge pressures
• 2. High permeability edema with high concentrations of large molecular weight proteins, cell
• (high protein concentration on lavage; thought to be due to uneven hypoxemic vasoconstriction, leading to high pressure in some capillaries --> rupture)

• - heroin, morphine
• - pneurogenic pulmonary edema

• dyspnea, orthopnea, paroxysmal nocturnal dyspnea -- sx thought to be from stimulation of J (juxtacapillary) receptors on the vagus nerve
• cough, may be pink frothy sputum
• crepitations on auscultation
• radiograph: septal lines, blotchy shadowing

• Interstitial edema:
• - Generally has little effect
• - Some evidence that lung compliance is reduced
• - Perivascular and peribronchial cuffing may increase pulmonary vascular and airway resistance
• 

Alveolar edema:

• 1. Mechanics
• - Lung compliance is reduced
• - Airway resistance is increased

• 2. Gas exchange
• - Hypoxemia due to shunt and ventilation-perfusion inequality
• - No CO₂ retention

3. Pulmonary vascular resistance increased