USG-guided pleural fluid aspiration: key steps

1. Position the patient

• Preferred: sitting upright, leaning slightly forward with arms supported on a table or pillow.
• If unable to sit: lateral decubitus with the affected side down, or semi-recumbent/supine with the head elevated.
• Keep the patient in exactly the same position from ultrasound scan through needle insertion.

2. Probe choice and initial scan

• Use a low-frequency curvilinear or phased-array probe (about 2-5 MHz) to locate fluid and diaphragm.
• Scan the posterolateral lower chest, usually posterior axillary to mid-scapular region.
• Begin low, identify the liver on the right or spleen/kidney on the left, then identify the bright curving diaphragm above it.
• Pleural fluid is usually an anechoic or hypoechoic black pocket above the diaphragm. Find the adjacent collapsed/mobile lung.

3. Probe position and orientation

• Place the probe in a posterior axillary or posterolateral position, with its long axis parallel to the intercostal space.
• Point the probe marker cephalad. With usual machine convention, the left side of the screen represents cephalad.
• Sweep cranial-caudal and fan the probe until you see:
  • Chest wall
  • Fluid pocket
  • Diaphragm
  • Lung edge moving into the fluid
  • Liver/spleen below the diaphragm

4. Select the safest puncture site

• The largest safe fluid pocket, not simply the deepest-looking pocket
• A path free of visible lung, diaphragm, liver, spleen, kidney, and loculations/septations
• A site generally in the posterior axillary or lateral region
• A level above the ninth rib to reduce risk of diaphragmatic and abdominal-organ injury
• Avoid a very medial posterior approach, particularly medial to the mid-scapular line, because intercostal vessels are more vulnerable there. Roberts and Hedges’ Clinical Procedures in Emergency, p. 252.

5. Needle orientation and handling

Needle entry

• Insert the needle/catheter just superior to the upper border of the rib.
• This avoids the main intercostal neurovascular bundle located along the inferior rib margin.
• Direct the needle toward the center of the fluid pocket, not toward the diaphragm or visible lung.

In-plane real-time technique, preferred for small/complex effusions

• Use a sterile probe cover and sterile gel.
• Keep the needle in the same plane as the long axis of the probe.
• Insert from the side of the probe and advance slowly, maintaining continuous visualization of the needle shaft and tip.
• If you cannot see the tip, stop advancing. Do not assume its location from the shaft alone.
• Align the needle angle with the ultrasound beam. A shallow angle improves the visible length of the needle, but it must still enter safely over the rib and into the fluid.

Out-of-plane technique

• Needle appears only as a bright dot. It is easier to lose the tip.
• Use only if experienced, with repeated small movements of the probe and needle to confirm that the dot is truly the needle tip.
• For a small pocket, in-plane visualization is generally safer.

6. Practical aspiration steps

1. Confirm patient, side, indication, allergy/anticoagulation status, imaging, and consent.
2. Monitor pulse oximetry. Have resuscitation equipment available.
3. Sterile preparation, draping, and local anesthetic down to the pleura.
4. Aspirate while advancing local anesthetic needle, which can help confirm the depth of pleural fluid.
5. For diagnostic aspiration, use a small needle/catheter and collect required specimens.
6. For therapeutic aspiration, use a small-bore catheter rather than a needle left in situ. The BTS statement specifically recommends a catheter for aspirations >60 mL.
7. Drain slowly. Avoid wall suction or vacuum bottles for routine therapeutic aspiration.
8. Stop if there is chest pain, persistent cough, chest tightness, worsening breathlessness, vasovagal symptoms, or poor tolerance.
9. A conservative maximum is 1.5 L in one session, unless a specialist protocol and pleural-pressure monitoring support a different plan.

7. After aspiration

• Reassess symptoms, pulse oximetry, puncture site, and hemodynamic status.
• Send fluid promptly for requested tests, commonly cell count/differential, protein, LDH, glucose, pH when infection is suspected, Gram stain/culture, and cytology as indicated.
• Obtain post-procedure imaging if symptoms, difficult/multiple passes, suspected complication, or concern for pneumothorax. Routine imaging is not always required after an uncomplicated, image-guided procedure.

Safety checklist

• See diaphragm first
• Choose the safest pocket
• Keep probe and patient position unchanged
• Needle goes above the rib
• Visualize the needle tip, not only the shaft
• Never advance if tip is not seen
• Stop drainage if symptoms develop