To perform a thoracentesis, first position your patient sitting at the edge of the bed with their arms resting on a table in front of her (if tolerated). Use ultrasound in the midscapular line to locate the superior border of the effusion, and mark the site 1-2 rib spaces lower. Do not go below the 9th rib to avoid subdiaphragmatic injury. Prep and drape the patient. Use local anesthetic in the skin and the planned intercostal tract. Introduce your catheter-over-needle at the superior margin of the rib to avoid injuring the neurovascular bundle at the inferior rib margin. Aspirate as you advance the needle. When pleural fluid is aspirated, stop advancing, and slide the catheter over the needle while holding the needle still. Attach tubing to drain the effusion. This can be done with a sterile bag to gravity, using a 3-way stopcock and push-pull technique, or using a vacuum sealed container. There is potentially increased risk of reexpansion pulmonary edema with a vacuum sealed container due to rapid drainage. Once the effusion is fully drained, remove the catheter and place a bandage over the site. A repeat chest x-ray allows for reassessment of the effusion and to check for iatrogenic pneumothorax.