Pleural effusions

Today we discussed pleural effusions

Most common causes of effusion in North America are CHF, pneumonia and cancer.

Indication for thoracentesis: Clinically significant effusion (i.e. over 10mm thick on u/s or lateral decubitus) with no clearly known cause.
If CHF with bilateral effusions, trial of diuresis first. 80% of CHF effusions are bilateral. If unilateral, should be tapped. 75% of CHF effusions resolve within 48h of diuresis.
If over 3d, thoracentesis is indicated.
If pt has SOB at rest, therapeutic in addition to diagnostic tap should be done (i.e. up to 1-1.5L).

No need to do routine CXR post except if air is obtained, c/p, cough, dyspnea.

Bloody effusion narrows Ddx somewhat to cancer, PE, trauma, infection (inc. pneumonia, TB)

Transudative: leading causes are CHF, cirrhosis, PE.
Exudative: leading causes are pneumonia, cancer, PE.


Light's criteria for exudative effusion:
Any of
protein level pleural:serum over 0.5
LDH pleural:serum of over 0.6
pleural LDH over 2/3 upper limit of normal for serum

Light's criteria are sensitive for exudate; may have transudates falsely called exudates. If clinical appearance suggests transudate but Light's criteria says exudate, measure albumin in serum vs. pleural fluid. If serum albumin is over 12 greater than pleural fluid almost all have transudative. This criterion is more specific for transudate, because it calls some exudates transudates.

If transudative effusion, determine which of CHF, cirrhosis, PE exists.
If exudative, further workup is needed, including cell counts, culture, glucose, cytology, TB studies.

Cell count:
Predominence of PMNs (over 50%) suggests acute process (parapneumonic, PE, pancreatitis). Only ~15% of malignant, and almost no tuberculous effusions have PMN over 50%.
Mononuclear predominance (lymphocytic) suggests chronic process; cancer, tuberculous, post-CABG.
Eosinophils (over 10%) is usually blood or air in pleural space. Unusual causes are Churg-Strauss, drugs (dantrolene, bromocripine, nitrofurantoin), asbestosis, parasitic infections.
Basophils: leukemic infiltration

Culture: yield is higher if also blood C+S.

Glucose: low glucose suggests empyema or malignant. Less commonly, hemothorax, TB, parasitic (e.g. paragonimiasis), primary inflammatory (e.g. RA, SLE, Churg-Strauss)

Cancer: cytology yield is highest for adenoca. Less useful for mesothelioma, squamous, lymphoma, sarcoma. VATS is choice if suspected ca but negative cytology. If lymphoma suspected, flow cytometry can show pleural fluid clonal population.

TB: tuberculous pleuritis effusions resolve, but pulmonary or extrapulm TB develop in >50%. Investigate for TB if lymphocytosis. Less than 40% have positive pleural cultures.

pH: indicated if parapneumonic or malignant suspected.

PE: Suspect if dyspnea out of keeping with size of effusion, pleuritic c/p, hemoptysis.

"Complicated pleural effusion"- i.e. an indication for drainage (pigtail or surgical chest tube) Any of
1) cloudy fluid
2) pH less than 7.2
3) Glucose less than 2.2
4) Pleural to serum glucose ratio less than 0.5
5) LDH over 1000
6) Neutrophils over 25000
7) effusion occupying 50% of hemithorax (relative indication)

Links
Click here for NEJM review of pleural effusions by Dr. Light himself
Click here for an excellent review from Clinical Infectious Diseases on empyema and parapneumonic effusions