Thoracentesis

Michael Mirza, MD
Christopher Bryczkowski, MD, FACEP

I. Introduction

• One of the many etiologies of dyspnea in the emergency department is a pleural effusion—an abnormal collection of fluid in the pleural space. 
• Removal of this fluid by needle aspiration is called a thoracentesis.
• Ultrasound allows the distinction between effusion and lung consolidations, and the diagnostic accuracy of ultrasound for pleural effusions is superior (93%), compared to auscultation (61%) and AP chest radiograph (47%), using chest CT as the reference standard.^1,2
• In addition, ultrasound can precisely identify the location of the fluid so that the chest wall can be marked in preparation for thoracentesis.³
• Thoracentesis can be both diagnostic and therapeutic for the patient. 
• Using ultrasound to guide this procedure can decrease the very high complication rate associated with it.^3-5

Indications

• Therapeutic intervention in a symptomatic patient
• Diagnostic evaluation of pleural fluid

II. Anatomy

• The pleural space is bordered by the visceral and parietal pleura.
• Fluid in the pleural space appears anechoic and is readily detected above the brightly echogenic diaphragm when the patient is in a supine position
• 
• Figure 1.  Visualizing a large pleural effusion, diaphragm and liver
  
  
• Video 1.  Large pleural effusion

III. Scanning Technique

• The ideal position for the patient is to sit upright leaning forward.
• A high frequency linear transducer (7.5 to 12 MHz) is the optimal choice for this procedure and placed on the patient’s back in the sagittal or transverse position.
  
  
• 
• Figure 2. Patient in sitting position with ultrasound probe placed over the thoracentesis area
  
  
• The lung is seen as an echogenic structure moving with respiration.
• Look for the deepest pocket of fluid superficial to the lung.
• Freeze the image and take note of the maximum permissible depth of needle insertion; this will prevent puncturing the lung. (Fig. 3)
  • Bear in mind that the lung is a moving structure and that the depth of fluid may vary with respiration.
    
    
• 
• Figure 3. Measurement of depth to lung parenchyma
  
  
• In order to visualize an effusion, the ultrasound beam will first image the chest wall, pleural line and the ribs.
• The edge of bone is echogenic and gives off a characteristic shadowing. (Fig. 4)
  
  
• 
• Figure 4. Pleural effusion with rib shadow. The transducer is placed perpendicular to the axis of the rib
  
  
• The area should be marked with a pen and then prepped and draped in standard surgical fashion before the procedure is performed.
• Watch movement of diaphragm for a few respiratory cycles to determine how cephalad the diaphragm moves and mark a location for needle insertion above the that point to insure avoiding the diaphragm during the procedure.
  
  
• 
• Illustration 1. Overview of technique

IV. Pathology

• Complications can include pneumothorax, puncture of lung tissue, cystic masses, empyema or mediastinal structures.
• Incidence of pneumothorax is greatly reduced with the use of ultrasound (0.97% with ultrasound vs 8.89% without ultrasound).⁶
• Color flow doppler can help differentiate free-flowing effusion versus a hypoechoic mass.²

V. Pearls and Pitfalls

• Failure to identify the deepest pocket of fluid
• Failure to identify the diaphragm, avoiding intra-abdominal injury
• Failure to use this diagnostic tool for all thoracentesis procedures
• Not appreciating that the lung is a moving structure.  The depth of fluid may vary with inspiration and expiration.

VI. References

1. Prina E, Torres A, Carvalho CRR. Lung ultrasound in the evaluation of pleural effusion. J Brasileiro de Pneumologia. 2014;40(1):1-5.
2. Soni NJ, Franco R, Velez MI, et al. Ultrasound in the Diagnosis & Management of Pleural Effusions. J Hosp Med. 2015;10(12):811-6.
3. Koh DM, Burke S, Davies N, Padley SP. Transthoracic US of the chest: clinical uses and applications. Radiographics. 2002;22:e1.
4. Barnes TW, Morgenthaler TI, Olsen EJ, et al. Sonographically guided thoracentesis and rate of pneumothorax. J Clin Ultrasound. 2005;33(9):442-6.
5. Jones PW, Moyers JP, Rogers JT, et al. Ultrasound-guided thoracentesis: is it a safer method? Chest. 2003;123:418-23.
6. Cavanna L, Mordenti P, Bertè R, et al. Ultrasound guidance reduces pneumothorax rate and improves safety of thoracentesis in malignant pleural effusion: report on 445 consecutive patients with advanced cancer. World J Surg Oncol. 2014;12:139.