Clinical Pearls & Morning Reports

Posted by Carla Rothaus

Published February 21, 2018

Do Light’s criteria fully distinguish transudates from exudates?

One of the first steps in the evaluation of patients with pleural fluid is to distinguish those who have inflammatory (exudative) effusions from those who have noninflammatory (transudative) effusions. According to Light’s criteria, a patient is considered to have an exudative effusion when any one of the following findings is present: a ratio of pleural fluid protein to serum protein higher than 0.5, a ratio of pleural fluid lactate dehydrogenase (LDH) level to serum LDH level higher than 0.6, or a pleural fluid LDH level higher than 200 IU per liter (or >67% of the upper limit of the normal range for serum LDH level).

Clinical Pearls

Q: Do Light’s criteria fully distinguish transudates from exudates?

A: The use of Light’s criteria for differentiating exudative from transudative effusion, initially described in 1972, has remained the standard method over the past 45 years. Although these criteria correctly identify nearly all exudates, approximately 25% of transudates are misclassified as exudates, especially in patients who have underlying congestive heart failure and have received diuretics.

Q: Does the presence of parapneumonic effusion affect mortality risk?

A: The most common exudative effusions are those associated with an underlying pneumonia, so-called parapneumonic effusions. Despite advances in the treatment of pneumonia, mortality is higher among patients who have an associated parapneumonic effusion than among patients with pneumonia and no effusion, and delays in drainage are associated with substantially higher mortality.

Figure 2. (10.1056/NEJMra1403503/F2) Management of Parapneumonic Effusions.

Morning Report Questions

Q: What are some of the management options for a large malignant effusion?

A: Malignant pleural effusion is associated with a poor prognosis, with a median survival of 4 to 7 months from the time of diagnosis. If the patient does not feel better after a therapeutic large-volume thoracentesis, something else is causing the dyspnea (e.g., pulmonary embolism or lymphangitic carcinomatosis). In such instances, further diagnostic testing should be performed; however, procedures that address the pleural space should not be performed. If the patient’s dyspnea has been alleviated with thoracentesis, the effusion was at least a major contributor to the dyspnea, and the dyspnea can be diminished regardless of whether the lung has reexpanded. If the lung has reexpanded, the patient can be considered for pleurodesis, placement of a tunneled pleural catheter, or combination approaches, whereas if the lung is nonexpandable, a tunneled pleural catheter is the treatment of choice. Although it is often a fear of referring health care providers, infection related to the tunneled pleural catheter occurs approximately 5% of the time and can usually be treated without removing the catheter.

Figure 3. (10.1056/NEJMra1403503/F3) Management of Malignant Pleural Effusions.

Q: What are some of the management options for pneumothorax?

A: Up to 70% of patients with a clinically stable pneumothorax can be treated with simple needle aspiration, which avoids hospitalization. Guidelines currently recommend the use of small-bore (14-French) chest tubes rather than large-bore chest tubes for patients with pneumothorax who have treatment failure or are not candidates for simple needle aspiration. When patients with a pneumothorax are treated with chest tubes, the lung usually expands and the air leak ceases within 3 days. If the lung does not expand fully within 3 to 5 days, consideration should be given to thoracoscopy. At thoracoscopy, blebs are stapled and an effort is made to create a pleurodesis, usually with pleural abrasion. Another method of treating prolonged air leak is to instill 1 ml of the patient’s own blood per kilogram of body weight through the chest tube. Alternatively, pleurodesis can be attempted through instillation of a sclerosing agent or the placement of endobronchial one-way valves, with the goal of reducing air flow across the visceral pleura. The valves are then removed after the pleural defect has healed, typically in 6 weeks. After a patient has had a spontaneous pneumothorax, the likelihood of a recurrence exceeds 50%.

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