this complication. Complications Major complications are pneumothorax (3–30%), hemopneumothorax, hemorrhage, hypotension (low blood pressure due to a vasovagal response) and reexpansion pulmonary edema. Minor complications include a dry tap (no fluid return), subcutaneous hematoma or seroma, anxiety, dyspnea and cough (after removing large volume of fluid). The use of ultrasound for needle guidance can minimize the complication rate. Follow-up imaging While chest X-ray has traditionally been performed to assess for pneumothorax following the procedure, it may no longer be necessary to do so in asymptomatic, non-ventilated persons given the widespread use of ultrasound to guide this procedure. Interpretation of pleural fluid analysis Several diagnostic tools are available to determine the etiology of pleural fluid. Transudate versus exudate First the fluid is either transudate or exudate. An exudate is defined as pleural fluid to serum total protein ratio of more than 0.5, pleural fluid to serum LDH ratio > 0.6, and absolute pleural fluid LDH > 200 IU or > of the normal. An exudate is defined as pleural fluid that filters from the circulatory system into lesions or areas of inflammation. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as blood. In the case of blood it will contain some or all plasma proteins, white blood cells, platelets and (in the case of local vascular damage) red blood cells. Exudate hemorrhage Infection Inflammation Malignancy Iatrogenic Connective tissue disease Endocrine disorders Lymphatic disorders vs Constrictive pericarditis Transudate Congestive heart failure Nephrotic syndrome Hypoalbuminemia Cirrhosis Atelectasis Trapped lung Peritoneal dialysis Superior vena cava obstruction Amylase A high amylase level (twice the serum level or the absolute value is greater than 160 Somogy units) in the pleural fluid is indicative of either acute or chronic pancreatitis, pancreatic pseudocyst that has dissected or ruptured into the pleural space, cancer or esophageal rupture. Glucose Glucose is considered low if pleural fluid value is less than 50% of normal serum value. The differential diagnosis for this is: rheumatoid effusion. The levels are characteristically low (<15 mg/dL). lupus effusion bacterial empyema malignancy tuberculosis esophageal rupture (Boerhaave syndrome) pH Normal pleural fluid pH is approximately 7.60. A pleural fluid pH below 7.30 with normal arterial blood pH has the same differential diagnosis as low pleural fluid glucose. Triglyceride and cholesterol Chylothorax (fluid from lymph vessels leaking into the pleural cavity) may be identified by determining triglyceride and cholesterol levels,