Thoracentesis

Thoracentesis, commonly known as a pleural tap or chest tap, is a procedure where excess pleural fluid is drained from the pleural space for diagnostic and/or therapeutic reasons. Ultrasound-guided thoracentesis performed by radiologists has been shown to have fewer complications than blind thoracentesis. A success rate of up to 90% has been demonstrated after failed blind thoracentesis. 

Indications

• symptomatic pleural effusions
• investigation of cause of pleural fluid collection, e.g. malignancy, infection, etc

Contraindications

• coagulopathy/thrombocytopaenia, anticoagulation or other bleeding disorders
• respiratory disease such as severe respiratory failure, intractable coughing, contralateral pneumonectomy, emphysema, suspected echinococcal disease or the inability to hold one's breath ⁷

Procedure

Thoracentesis can be performed blind, partially imaged-guided or image-guided (usually ultrasound but may be CT). Below the technique for an ultrasound-guided  therapeutic thoracentesis with a trocar technique is outlined as this is the most commonly performed in radiology. Seldinger technique is an alternative method. 

Preprocedural evaluation

• review history, pathology results and prior imaging
  • e.g. 75% of pleural effusions secondary to congestive cardiac failure will resolve with two days of diuresis and thoracentesis should be reserved for refractory cases ³
• obtain informed written consent
• completion of a "time-out" with nursing staff

Positioning/room set up

• patient sitting on edge of bed, leaning forward with arms on a table
• monitoring (BP, pulse rate, SpO2)
• access from behind the patient

Equipment

• ultrasound with CH-4 probe
• sterile pack including wash, gown and gloves, drape, ultrasound cover and sterile gel
• long hypodermic needle, syringe and lignocaine
• scalpel
• thoracentesis/paracentesis catheter-over-needle set
• three-way tap and drainage bag
• dressings

Technique

• pre-procedure ultrasound to confirm presence of drainable pleural effusion
• sterile glove and gown followed by sterile preparation and drape
• subcutaneous and deep infiltration to pleura of local anaesthetic under ultrasound guidance
• small skin nick with scalpel
• under ultrasound guidance, introduction of thoracentesis needle along the superior margin of the rib, aspirating while advancing until pleural fluid is aspirated; catheter is then slid off needle
• connection of three-way tap and drainage bag and airtight dressing applied
• for diagnostic thoracentesis 50 mL of fluid is usually required ³

Postprocedural care

• volume to be drained varied depending on number of prior taps
  • for first-time taps ~1500 mL (or until symptoms such as chest pain commence) is recommended to reduce the occurrence of re-expansion pulmonary oedema ^4,5
• requirement for post-thoracentesis chest x-ray to assess for pneumothorax is debated; literature has demonstrated there is a very low risk of pneumothorax in asymptomatic patients ¹
• patient should be advised of the risk of pneumothorax and not to fly for one week ⁶

Complications

Common complications from thoracentesis include ^1,4:

• pain (~20%)
• cough
• vasovagal reaction
• re-expansion pulmonary oedema (~7.5%)

Serious, but less common, complications from thoracentesis include ^1,3,4:

• pneumothorax (<5%)  including tension pneumothorax and hydropneumothorax
  • may require treatment with an intercostal catheter (~20%)
• haemothorax (1%) or chest wall haemorrhage
• intercostal nerve, artery or vein damage
• trapped lung
• non-diagnostic or non-therapeutic procedure
• liver and splenic trauma from inadvertent puncture
• pleural infection or empyema (rare; <1 in 2000)
• air embolism

Outcomes

• in malignant pleural effusions the average duration of symptom relief is 4 days and 99% of patients will reaccumulate pleural fluid ⁵