Pleural effusion or fluid around lungs
A pleural effusion is the accumulation of fluid in the pleural space. It is not a diagnosis but a manifestation of an underlying disease process. Although there are many causes, the most common are heart failure, pneumonia and cancer.
Pleural effusions are common. The epidemiology is specific to the underlying cause.
Pleural effusions are classified by pathophysiology into transudates and exudates. Transudate results from an imbalance between hydrostatic and oncotic pressure while an exudate results when pleural or local capillary permeability is altered.
A pleural fluid protein content of less than 25 g/L or more than 35 g/L normally differentiates between transudate and exudate; if the protein concentration lies between 25 and 35 g/L, then Light's criteria will be required to distinguish the two.
Scope of disease
Gradual fluid accumulation and progressive dyspnoea is the usual manifestation of pleural effusion.
Shortness of breath is the principal complaint of patients with pleural effusions. The degree of fluid sufficient to cause dyspnoea varies according to the underlying state of the lungs. An otherwise healthy individual may tolerate up to several litres of fluid before experiencing dyspnoea on exertion. On examination the trachea may be deviated away from the (very large) effusion; there may be decreased expansion on the affected side, dullness to percussion and absent breath sounds.
Causes of transudative pleural effusion - cardiac failure, mitral stenosis, constrictive pericarditis, pulmonary embolism, liver cirrhosis, nephrotic syndrome, hypoalbuminaemia and superior vena cava obstruction.
Causes of exudative pleural effusion - malignancy ( lung , mesothelioma, breast, genito- urinary , gastrointestinal ), pneumonia, pulmonary infarction, rheumatoid disease, SLE, drugs ( Amiodarone, phenytoin, methotrexate ) , pancreatitis, haemothorax, and chylothorax.
Light 's criteria to differentiate between transudate and exudative pleural effusion:
The diagnosis of exudative is the present of one or more of the following three points:
-Ratio of pleural fluid protein level to serum protein level >0.5
-Ratio of pleural fluid lactate dehydrogenase (LDH) level to serum LDH level >0.6
-Pleural fluid LDH level more than 2/3 the upper limit of normal for serum LDH
It is important to take a detailed drug history and also screen for symptoms and signs of the underlying diseases. A history of coagulation disorder is also pertinent as thoracocentesis may be required when the cause is unknown.
Serum albumin and lactate dehydrogenase (LDH)
These two investigations are usually required to provide comparison with the results of pleural fluid analyses.
Postero-anterior and lateral films should be performed. An accumulation of approximately 200 mL of fluid is required before it is detectable on the PA chest film (blunting of the costophrenic angle); 500 mL would obscure the hemidiaphragm . On a lateral film, 50 mL of fluid is generally detectable.
Pleural fluid aspiration (thoracocentesis)
The indication for pleural fluid aspiration is for clinically significant effusions with no known cause. Aspiration should not be undertaken in patients with bilateral effusions with clinical features suggestive of a transudative effusion (unless there are atypical features or the patient fails to respond to therapy).Ultrasound-guided aspiration is recommended for small or loculated effusions.
The pleural fluid should be inspected and sent for microbiology (bacterial and TB cultures), cytology (successful in identifying 60% of malignant effusions) and clinical chemistry analysis (protein, LDH, pH, glucose, differential cell count; ). Additional investigations are requested on clinical suspicion of pancreatitis (pleural fluid amylase), haemothorax (pleural fluid haematocrit) or chylothorax (pleural fluid lipid and chylomicrons level;
Bloody effusions can result from trauma, malignancy, tuberculosis or pulmonary infarction (pulmonary embolus). A cloudy or turbid appearance would suggest infection (empyema) or chylothorax (lymph in the pleural space,)
CT of the thorax is a useful investigation when initial investigations fail to determine the underlying cause. It is also useful to help differentiate between benign and malignant disease (such as mesothelioma). Pleural biopsies can be taken with CT guidance.
Results and interpretation of fluid analysis:
If glucose level less than 3.3 mmol/l indicates tuberculosis, rheumatoid disease and malignancy.
If pH less than 7.2 indicates infection, need for chest tube drainage, rheumatoid disease and malignancy.
If increase in number of lymphocytes ( lymphocytosis ) indicates malignancy and tuberculosis.
If amylase is more than normal consider pancreatitis.
if haemotocrit is more than 50% normal consider hemothorax.
If triglycerides more than 2.4 mmol/l consider chylothorax.
Percutaneous pleural biopsies
Percutaneous pleural biopsies are usually performed to obtain tissue samples for suspected malignant disease of the pleura. There is an approximate 10% risk of pneumothorax, 2% risk of haemothorax (less than 1% risk of death from haemorrhage) and 40% risk of needle tract invasion if the underlying diagnosis is mesothelioma (hence the requirement for needle site irradiation).
Drainage of effusion
In patients with transudative effusions (and in some cases of exudative effusion), treatment of the underlying cause can result in the resolution of effusion. In patients with dyspnoea from accumulating fluid, percutaneous pleural aspiration, narrow bore pigtail catheter or formal chest tube drainage may be required for symptomatic relief in conjunction with treatment of the underlying cause. It is important not to remove more than 1 litre per hour to minimize the risk of re-expansion pulmonary oedema.
Chemical pleurodesis (for malignant effusions)
There is an extremely high recurrence rate after drainage of a malignant effusion. Once drainage has been achieved and lung re-expansion confirmed on chest X-ray, a chemical sclerosant (talc, tetracycline, bleomycin) may be instilled to promote an inflammatory reaction and pleurodesis.
Surgical management is largely confined to diagnosis or the treatment of malignant effusions (occasionally surgical biopsies can assist in the diagnosis of an underlying cause after initial investigations have failed to identify a diagnosis).
A video-assisted thoracoscopic (VATS) approach is usually employed. With the patient in a lateral position, a VATS camera is introduced into the pleural cavity. The fluid is drained and sent for cytology, and the lung and pleural surfaces are carefully inspected. Biopsies are taken of any suspicious nodules. Only after histopathological confirmation of malignancy has been obtained is pleurodesis undertaken. The lung must fully expand (otherwise a pleuro-peritoneal shunt may be used instead) for a successful pleurodesis; talc is usually the preferred sclerosant. Pleurectomy is rarely performed.
For patients in whom the lung is trapped by tumour deposits, failure of contact with the chest wall will result in unsuccessful pleurodesis. In such cases a pleuro-peritoneal shunt is placed from the pleural into the abdominal cavity. A small one-way pump is situated subcutaneously for patients to ensure continuous drainage of the pleural space.
Long-term pleural drain
A long-term pleural drain is usually reserved for patients who are not fit for surgery, or for patients with terminal illness where repeated hospitalizations can be avoided.
The prognosis is related to the underlying cause.
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