![]() This can be caused by an elevated pulmonary capillary pressure with heart failure, excess ascites with cirrhosis or low oncotic pressure with the nephrotic syndrome ( 36).Ĭriteria known as Light’s criteria define the exudative and transudative effusion. When systemic factors are altered producing a pleural effusion, the fluid has low protein and lactate dehydrogenase levels and is called a transudate. Local factors include leaky capillaries and pleural inflammation due to infection, infarction, or tumor. When local factors are altered, the fluid is rich in protein and lactate dehydrogenase (LDH) and is called an exudate. This regulated fluid balance can be disrupted when either local or systemic derangements occur. However if the normal flow of fluid is disrupted, with either too much fluid being produced or not enough being removed, fluid accumulates resulting in a pleural effusion. At any one time there is about 20 mls of fluid in each hemithorax and the layer of fluid is 2 to 10 micrometers thick ( 36). This fluid is then removed by the lymphatics in the parietal pleura. Approximately 15 mls per day of fluid enters this potential space primarily from the capillaries of the parietal pleura. A thin layer of fluid is always present in this space to allow for lubrication so that the lung may glide in the chest during inspiration and expiration. PATHOPHYSIOLOGYĪ pleural effusion is, simply put, an abnormal fluid collection in the chest between the visceral and pleural surfaces. The etiologies of pleural effusions as a whole, and then more specifically the various specific findings of pleural effusions resulting from infectious diseases, will be examined. ![]() ![]() This chapter will help to elucidate the broad differential diagnosis that must be entertained when a physician is faced with a pleural effusion. Infectious processes including bacteria, viruses, tuberculosis, atypical mycobacterium, fungus, as well as parasites account for a substantial percentage of these effusions. Pleural effusions are produced by a wide variety of causes. ![]()
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