Pleural Tap (Thoracentesis) - Steps

Indications

Diagnostic: 50 mL of fluid obtained for lab studies (protein, LDH, cytology, culture, glucose)
Therapeutic: Relief of dyspnea from large effusion - typically up to 1-1.5 L removed

Contraindications

No absolute contraindications
Relative: overlying cutaneous infection/herpes zoster, coagulopathy (INR >1.6, platelets <50,000/mm³) - risk virtually eliminated with ultrasound guidance
Loculated effusions and mechanically ventilated patients require ultrasound guidance

Equipment

Sterile gloves, drapes, antiseptic solution (0.5% chlorhexidine in spirit)
1% or 2% lignocaine (15-20 mL), 25-gauge needle for skin wheal, larger needle for deep infiltration
For diagnostic: 22-gauge 2-inch needle (or spinal needle for larger patients), syringe
For therapeutic: Over-the-needle catheter (e.g. 8-Fr catheter over 18-gauge needle) with three-way tap, 60 mL syringe, sterile collection container
Pulse oximeter; atropine at bedside (for vasovagal reaction)
Ultrasound strongly recommended

Step-by-Step Technique

Step 1 - Consent and Pre-procedure Preparation

Obtain informed consent
Send peripheral blood for serum protein and LDH (if diagnostic)
Monitor SpO2; administer supplemental O2 as needed
Keep atropine at bedside

Step 2 - Patient Positioning

Position the patient sitting upright on the edge of the bed, leaning forward slightly with arms resting on a bedside table or Mayo stand, head turned away from the operator.

Patient positioned leaning forward on bed table - ideal position for chest aspiration (Pye's Surgical Handicraft)

If upright is not possible: lateral decubitus (affected side down, back at bed edge, posterior axillary line) or supine with head elevated (midaxillary line used).

Step 3 - Site Selection

Use ultrasound to locate the top of the effusion and the diaphragm
Entry site: 1-2 intercostal spaces below the highest level of the effusion, in the midscapular or posterior axillary line
Entry must be above the 9th rib (avoid diaphragm/liver/spleen injury)
Do NOT go medial to the midscapular line (intercostal artery runs more centrally here)
At least 10 mm fluid thickness should be confirmed by ultrasound at the chosen site
Mark the site with a skin marker

Triangle of Safety (Pye's): bordered anteriorly by the anterior axillary line, posteriorly by the mid-axillary line, inferiorly by a horizontal line at the level of the nipple (men) or 4th interspace (women). This zone contains no dangerous structures.

Step 4 - Aseptic Preparation

Clean skin with chlorhexidine in spirit; apply sterile drapes
Operator scrubs and dons sterile gloves

Step 5 - Local Anaesthesia

Create a skin wheal with 25-gauge needle at the upper border of the lower rib (to avoid the intercostal neurovascular bundle, which runs in the costal groove at the inferior border)
Advance the needle along the track, infiltrating 15-20 mL of 1% lignocaine in layers, down to and including the parietal pleura
Wait at least 3 minutes for full effect before proceeding

Step 6 - Needle/Catheter Insertion

Assemble the aspiration apparatus: needle (or catheter) attached to a three-way tap and 60 mL syringe, with a sterile tube on the side arm
In male adults, a small skin incision may ease needle passage
Insert the needle at the upper border of the rib with a combination of steady pressure and a twisting motion
To limit inadvertent deep penetration (especially for inexperienced operators), artery forceps can be clipped ~5 cm from the tip of the needle
A distinct loss of resistance is felt as the needle passes through the parietal pleura into the pleural space

Step 7 - Aspiration

Aspirate by pulling back on the syringe - fluid (or air) flows into the syringe
Turn the three-way tap to redirect fluid through the side arm into a sterile container
Repeat this cycle until the desired volume is removed
Diagnostic: 50 mL is sufficient
Therapeutic: up to 1-1.5 L (do not exceed 1.5 L in one session to avoid re-expansion pulmonary oedema)

Step 8 - Needle Withdrawal and Dressing

Remove needle/catheter while the patient exhales (or performs Valsalva) to minimise air entry
Apply a sterile dressing over the puncture site

Step 9 - Post-procedure

Chest X-ray post-procedure - required if air was aspirated, if the patient is on mechanical ventilation, or if pneumothorax is suspected (not mandatory in all cases)
Monitor for complications

Complications to Watch For

Complication	Notes
Pneumothorax	Most common; risk greatly reduced with ultrasound guidance
Haemothorax	From intercostal vessel injury - avoid inferior rib border
Re-expansion pulmonary oedema	Limit removal to <1.5 L per session
Dry tap	Needle too short or site too high; reposition
Vasovagal reaction	Have atropine ready
Infection/empyema	Strict aseptic technique
Diaphragm/liver/spleen puncture	Stay above 9th rib

Sources:

22nd Edition Pye's Surgical Handicraft, Chapter 17 (Chest Aspiration Technique)
Roberts and Hedges' Clinical Procedures in Emergency Medicine, Chapter 9 (Thoracentesis)
The Washington Manual of Medical Therapeutics (Diagnostic Procedures)

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