Difference Between Pleural Effusion and Pulmonary Edema

Pleural Effusion vs Pulmonary Edema

Pleural effusion and pulmonary edema are two common lung conditions. These two share some aspects of the pathophysiology and cardiac failure, fluid overload, liver failure, and renal failure can cause both these conditions.

Pleural Effusion

We have two lungs in the thoracic cavity. Lungs are covered with two thin tissue layers called the pleura. The inner layer is adhered to the outer surface of the lung and is the visceral pleura. The layer lining the thoracic cavity is the parietal pleura. The potential space between the two layers of the pleura is the inter-pleural space. Collection of fluid inside this potential space is known as pleural effusion.

There are two types of pleural effusions; they are transudative effusions and exudative effusions. Pleural effusions may occur due to following reasons.

  • Elevated hydrostatic pressure of pulmonary veins (cardiac failure, constrictive pericarditis, pericardial effusion and fluid overload),
  • Low serum proteins (chronic liver disease, protein losing enteropathy, nephrotic syndrome, widespread skin lesions, hypothyroidism and burns),
  • Infections (pneumonia, lung abscess, tuberculosis),
  • Inflammation (systemic lupus erythematosus, connective tissue disorders and rheumatoid arthritis),
  • Malignancy (primary lung cancers and metastatic tumors)

Elevated hydrostatic pressure and low serum proteins give rise to transudative effusions while infections, inflammation and malignancies give rise to exudative effusions. Patients with pleural effusions present with shortness of breath, reduced exercise tolerance, and pleuritic type chest pain. Leg swelling, dizziness, ischemic chest pain, orthopnea, paroxysmal nocturnal dyspnea, parotid swelling, gynecomastia, abdominal distention, chronic alcohol use, chronic diarrhea, frothy urine, skin rashes, malar rash, weight loss, and loss of appetite may give clues towards the primary cause of the effusion.

 On examination, there will be rapid breathing, diminished chest expansion, dull percussion note, diminished breath sounds over the affected area, and bronchial breathing above the area. Chest X-ray, ECG, full blood count, ESR, blood urea, electrolytes, spirometry, sputum microscopy, culture and arterial blood gas analysis are the routine investigations.

 Treating the underlying cause will relieve the effusion. If symptomatic, effusion can be drained. Pleural fluid can then be sent for protein, glucose, pH, LDH, ANA, complement, rheumatoid factor and cytology). In recurrent pleural effusions, pleurodesis with tetracycline, bleomycin, or talc is an option.

Pulmonary Edema

Pulmonary edema is due to elevated hydrostatic pressure of draining pulmonary veins. Poor left ventricular function is the commonest cause. Left ventricular failure can be due to heart attacks, arrhythmias, myocarditis, endocarditis, fluid overload, renal failure, systemic hypertension, and ventricular outflow tract obstruction. Pulmonary edema is one of the manifestations of poor ventricular function and a common cause for emergency admission.

Pulmonary edema presents as pink frothy sputum, cough, and shortness of breath, which increases while lying down. This is a medical emergency. On examination, there will be bilateral basal crepitations, high blood pressure and a rapid heart rate. Patient should be given a bed. Diuretics to clear the lungs, lower blood pressure, and treat the underlying cause for heart failure are the basic principles of management.

Pulmonary Edema vs Pleural Effusion

• Pleural effusion is the collection of fluid outside lungs while pulmonary edema is the collection of fluid inside lungs.

• Pleural fluid collects in the pleural space while edema fluid collects in alveoli.

• Pleural effusion gives pleuritic type chest pain while pulmonary edema doesn’t.

• Pleural effusion reduces chest expansion, is dull to percuss while pulmonary edema is not.

• Basal creps are prominent in pulmonary edema while bronchial breathing and aegophony (egophony) are seen in pleural effusion.

• Pleural effusion diminishes costophrenic angles and is visible as a crescent shape at lower lung fields in the chest X-ray. In pulmonary edema, alveolar edema, Kurly B lines, cardiomegaly, dilatation of the upper lobe arterioles, and effusion may be seen in chest X-ray.