Most diagnostic thoracenteses are performed on the ward and do not require radiologic guidance. The value of radiology guidance for aspiration is to simultaneously increase the likelihood of obtaining pleural fluid, and to decrease the risk of pneumothorax. Radiologic guidance is most useful when there is a small amount of fluid. The capability to guide and follow the needle with ultrasound or CT enhances the diagnostic yield. Similarly, by avoiding blind needle stick, pneumothorax is less likely to develop.
Aspirated material is sent for diagnosis to the lab.
Gram stain, culture, cytology and chemistry evaluations are performed. Ph levels also are obtained. These catheters permit therapeutic thoracentesis with evacuation of serous or noninfected fluid. If diagnostic aspiration reveals infection by gram stain or culture, percutaneous drainage is indicated. For large or free-flowing empyemas, ultrasound is used as the guidance system.