What are the steps for performing a thoracentesis (pleural effusion tapping)?

Thoracentesis Procedure Steps

Thoracentesis should be performed using ultrasound guidance to identify the optimal insertion site, followed by sterile technique with the patient positioned upright, inserting a small-gauge needle (21-22 gauge for diagnostic, larger for therapeutic) into the pleural space, typically in the mid-scapular or posterior axillary line, one to two intercostal spaces below the fluid level. 1, 2

Pre-Procedure Preparation

Patient Assessment and Imaging

• Obtain chest radiography to determine effusion size, laterality, and presence of mediastinal shift 3
• Perform ultrasound examination immediately before the procedure to accurately locate fluid, identify loculations or septations, and mark the optimal insertion site 1, 3, 4
• Assess for contraindications including minimal effusion volume, bleeding diathesis, anticoagulation, mechanical ventilation, and severe renal failure 3

Patient Positioning

• Position the patient sitting upright, leaning forward over a bedside table with arms supported 2, 5
• Alternative positioning includes lateral decubitus if the patient cannot sit upright 5

Procedure Technique

Site Selection and Preparation

• Use ultrasound to identify the insertion site in real-time, typically in the mid-scapular or posterior axillary line, one to two intercostal spaces below the upper border of the effusion 1, 4
• Mark the site after ultrasound identification 4
• Prepare the site with sterile technique using antiseptic solution and drape the area 2, 5

Needle Insertion

• Administer local anesthesia (lidocaine) to the skin, subcutaneous tissue, and down to the pleura 2, 5
• For diagnostic thoracentesis requiring small volumes (35-50 mL), use a small-gauge needle (21 or 22 gauge) to minimize pneumothorax risk 2
• For therapeutic thoracentesis, use a larger bore needle or catheter system 2
• Insert the needle over the superior border of the rib to avoid the neurovascular bundle that runs along the inferior rib margin 5
• Advance the needle while applying gentle negative pressure until pleural fluid is aspirated 5

Fluid Removal

• For diagnostic purposes, obtain at least 25 mL (ideally 50 mL) of pleural fluid for laboratory analysis 3
• For therapeutic thoracentesis, limit fluid removal to 1-1.5 L per session unless pleural pressure monitoring is available 6, 3
• Stop the procedure immediately if the patient develops cough during fluid removal, as this signals excessive negative pleural pressure 6
• Monitor for symptoms of chest discomfort or dyspnea during the procedure 6

Pleural Pressure Monitoring (When Available)

• Consider pleural manometry to detect unexpandable lung and minimize risk of re-expansion pulmonary edema when removing large volumes 7, 4
• Initial pleural pressure <-10 cm H₂O suggests trapped lung 8, 3
• Pressure >19 cm H₂O with removal of 500 mL or >20 cm H₂O with removal of 1 L predicts trapped lung 1

Post-Procedure Management

Immediate Care

• Remove the needle and apply an occlusive dressing 5
• Obtain a post-procedure chest radiograph to assess for pneumothorax, residual fluid, and lung expansion 8
• Monitor vital signs and respiratory status 5

Fluid Analysis

• Send fluid for laboratory testing to distinguish transudates from exudates 2, 5
• Include chemical studies, microbiological cultures, and cytological analysis as indicated 5
• Immunohistochemistry provides increased diagnostic accuracy when malignancy is suspected 5

Critical Pitfalls to Avoid

• Do not remove the chest tube prematurely if trapped lung is suspected, indicated by lack of mediastinal shift with large effusion or initial pleural pressure <-10 cm H₂O 8
• Do not proceed with large-volume removal in patients with ipsilateral mediastinal shift without pleural pressure monitoring, as they have increased risk of precipitous pressure drops 6
• Avoid blind thoracentesis without ultrasound guidance, which significantly increases pneumothorax risk 1, 3, 4
• Do not use large-gauge needles for small diagnostic samples, as this increases complication rates 2

Complications Monitoring

• Pneumothorax is the most common major complication, minimized by ultrasound guidance and small-gauge needles 2, 4
• Re-expansion pulmonary edema risk increases with rapid removal of large volumes 3, 7
• Monitor for bleeding, infection, and organ laceration 3
• If dyspnea is not relieved after thoracentesis, investigate other causes including lymphangitic carcinomatosis, atelectasis, thromboembolism, tumor embolism, and endobronchial obstruction 1, 3