Thoracocentesis (Pleural Tap)

1. Definition

Thoracocentesis (also called thoracentesis or pleural tap) is a procedure in which pleural fluid is aspirated from the pleural space using a needle or catheter for diagnostic and/or therapeutic purposes.

2. Indications

A. Diagnostic Thoracocentesis

Performed to determine the cause of pleural effusion.

Indications

• New pleural effusion of unknown etiology
• Unilateral effusion
• Asymmetric effusion
• Effusion with fever or sepsis
• Suspicion of:
• Tuberculosis
• Malignancy
• Parapneumonic effusion
• Empyema
• Pulmonary embolism
• ICU patient with unexplained respiratory deterioration

Exception (when NOT mandatory)

• Bilateral small effusions with clear CHF picture responding to diuretics

B. Therapeutic Thoracocentesis

Performed to relieve symptoms or prevent complications.

Indications

• Moderate–large effusion causing:
• Dyspnea
• Hypoxia
• Lung compression
• Tense effusion
• Loculated effusion (diagnostic + partial drainage)
• Empyema (initial decompression)
• Malignant effusion (symptom relief)

3. Contraindications

Absolute

• None (life-saving procedure if severe respiratory distress)

Relative

Exam Pearl: Thoracocentesis is not contraindicated in anticoagulated patients if ultrasound-guided and benefit outweighs risk.

4. Anatomy & Surface Landmarks

Key Anatomical Principles

• Fluid accumulates posteriorly and basally
• Intercostal neurovascular bundle runs along lower border of rib
• Always insert needle just above upper border of rib

Classical Landmark Technique

• Patient sitting upright
• Tap at:
• 7th–9th intercostal space
• Mid-scapular or posterior axillary line

 Landmark-only technique is obsolete in ICU.

5. Role of Ultrasound (POCUS)

Why Ultrasound is Mandatory

• Confirms presence of fluid
• Estimates volume
• Identifies septations / loculations
• Determines safest site
• Reduces pneumothorax by >70%
• Allows real-time needle guidance

Ultrasound Signs

6. Pre-Procedure Checklist (ICU-Ready)

Patient Assessment

• Indication confirmed
• Review CXR / CT / ultrasound
• Coagulation status
• Platelet count
• Oxygen requirement

Consent

• Explain:
• Pain
• Bleeding
• Pneumothorax
• Re-expansion pulmonary edema

Equipment

• Sterile gloves, drapes
• Local anesthetic (1–2% lignocaine)
• 10–20 mL syringe + needle 20–22 gauge Or 21G spinal needle (longer reach in obese patients)
• 3-way stopcock
• Vacuum bottle or syringe
• Ultrasound with probe cover
• Collection bottles (EDTA, sterile, plain)

7. Step-by-Step Procedure

Step 1: Positioning

• Sitting upright, leaning forward
• ICU: lateral decubitus if unable to sit

Step 2: Ultrasound Localization

• Identify:
• Maximum fluid pocket
• Diaphragm
• Lung edge
• Mark site

Step 3: Aseptic Preparation

• Full sterile technique
• Local infiltration:
• Skin → subcutaneous tissue → periosteum → pleura

Exam Pearl: Pain occurs when parietal pleura is infiltrated.

Step 4: Needle Insertion

• Insert just above rib
• Aspirate continuously
• Feel “give-way” as pleura breached

Step 5: Fluid Aspiration

• Diagnostic: 20–50 mL
• Therapeutic:
• Maximum recommended: 1–1.5 L per sitting

 Stop if:

• Chest pain
• Persistent cough
• Dyspnea
• Vasovagal symptoms

Step 6: Completion

• Withdraw needle
• Apply occlusive dressing
• Monitor vitals

8. Pleural Fluid Analysis (High-Yield Table)

Light’s Criteria

Exudate if any one:

• Pleural protein / serum protein >0.5
• Pleural LDH / serum LDH >0.6
• Pleural LDH >⅔ upper limit of normal serum LDH

9. Volume Limits & Re-Expansion Pulmonary Edema (REPE)

Why limit drainage?

• Rapid lung re-expansion → capillary leak

Risk Factors

• Young age
• Large chronic effusion
• Rapid drainage
• Negative pressure suction

Clinical Features

• Cough
• Chest tightness
• Hypoxia
• Pink frothy sputum (rare)

10. Complications

Exam Pearl: Routine post-procedure CXR is not mandatory if ultrasound-guided and asymptomatic.

11. Thoracocentesis in Special Situations

A. Mechanically Ventilated Patients

• Higher pneumothorax risk
• Prefer:
• Ultrasound guidance
• Small-bore catheter
• Avoid high PEEP during procedure

B. Coagulopathy

• Not an absolute contraindication
• Ultrasound + small needle → safe
• Platelets >20–30k acceptable in emergencies

C. Loculated Effusions

• Thoracocentesis often insufficient
• Consider:
• Chest tube
• Intrapleural fibrinolytics

12. Thoracocentesis vs Chest Tube