USG guided thoracentesis is a procedure to aspirate pleural fluid using ultrasound guidance. It has several advantages over non-US guided thoracentesis, including being highly accurate which decreases complications. The key steps are to identify pleural anatomy like fluid, diaphragm and lung under ultrasound and then perform the procedure under real-time visualization of instruments to safely drain fluid. Post procedure chest x-ray is done to identify any complications like pneumothorax. USG guidance improves safety and accuracy of characterizing pleural disease and draining pleural fluid.

1. USG GUIDED THORACENTESIS
Dr.Suhas B
Resident
(MD Radio-Diagnosis)

2. Introduction
• Thoracentesis/pleural tap is a procedure that is done to
aspirate a sample of fluid from pleural cavity.
• USG guided thoracentesis are highly accurate and reliable.
Using ultrasound to guide this procedure can decrease the
very high complication rate associated with it.
• The goals are to improve accuracy and safety in the
characterization of pleural disease and performance of pleural
access procedures.
Indications:
• Therapeutic intervention in symptomatic patient (Emergency
and out-patient)

3. 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.
• The intercostal muscles appear as hypoechoic, linear shadows of soft
tissue density, containing echogenic fascial planes. The ribs appear as
repeating curvilinear structures with a deeper, hypoechoic, posterior
acoustic shadow that can be mistaken for pleural fluid. The parietal and
visceral pleura normally appear as a single, bright echoic line no wider
than 2 mm.
• The change in acoustic impedance at the pleura-lung interface results in a
series of echogenic parallel lines equidistant from each other just deep to
the pleural line.
• The diaphragm typically appears as an echogenic line approximately 1 mm
thick; downward (caudad) movement of the diaphragm should be seen
with inspiration.
• When the lung is compressed by a surrounding pleural effusion, it appears

5. Pre-requisites
• A 3.5 to 5.0 MHz transducer with a convex sector design
works well for pleural imaging. Cardiac transducers are
particularly effective, as they are designed with a small
footprint, allowing scanning between rib interspaces.
• The chest radiograph is reviewed before the procedure to
confirm the side of the pleural abnormality and the expected
location of any masses or loculated accumulations of fluid.
• Informed consent for the procedure is obtained, and clotting
studies should be confirmed to be adequate.
• Patients should take light food and stop all anti-coagulant
medications 2 days before the procedure.

6. Contraindications
• Uncertain fluid location by examination
• Minimal fluid volume
• Altered chest wall anatomy
• Pulmonary disease severe enough to make
complications life threatening
• Bleeding diatheses or coagulopathy
• Uncontrolled coughing
• Uncooperative patient
• Chest wall cellulitis

7. Patient preparation
• Pleural fluid is obedient to the law of gravity, so pleural fluid collects in the
dependent portion of the thorax (unless loculated).
• The usual position for ultrasound examination of a pleural effusion is for the patient
to sit with arms extended and resting on a firm surface that is just below the level of
the shoulders.
• Raising the patient’s ipsilateral arm up to or above their head widens the intercostal
spaces and facilitates scanning.
• When the patient is sitting, the entire back is accessible for ultrasonographic
examination, so free-flowing pleural fluid is readily identified in the dependent lower
thorax.
• critically-ill patients are positioned in supine with the ipsilateral arm held across the
chest towards the opposite side.
• The region of access should be made sterile by betadine application followed by
surgical spirit swabbing.

9. Scanning technique
• Transducer is perpendicular to the chest to allow for accurate estimates of
pleural fluid. When the transducer is oblique, over and underestimation of
fluid can occur.
• The transducer is oriented to scan between the ribs, as ribs block
transmission of ultrasound. This orientation yields an image where the
adjacent rib shadows appear on either side of the image on the screen. By
moving the transducer longitudinally from one interspace to another,
multiple interspaces may be examined in a short time.
• The diaphragm and liver or spleen should be identified first.
• The distance from the transducer to the pleural fluid should also be noted.
The probe is then rotated 180 degrees to visualize the pleural fluid
between the ribs to ensure that there is only fluid visualized ie. no lung,
diaphragm, or liver or spleen. This area should correspond with the first
mark and is the site of insertion.

10. Pleural effusion with rib shadow.
The transducer is placed
perpendicular to the axis of the rib.
Muscle, fluid, lung, and
measurements.

11. Pleural fluid characteristics
Three ultrasonographic criteria must be satisfied to ensure the presence of a
pleural effusion:
• The finding of an echo free space (appears black and without stippling)
within the thoracic cavity
• The finding of typical anatomic boundaries that surround the effusion: the
inside of the chest wall, the diaphragm, and the surface of the lung
• The presence of dynamic characteristics that are typical of pleural fluid,
such as diaphragmatic movement, lung movement, movement of
echogenic material within the fluid (septations, cellular debris, fronds), and
changes in the shape of the pleural effusion with respiratory cycling.
Atypical Appearances
• Complex loculated effusions may be hyperechoic and be located in a
nondependent part of the thorax. Hemothorax and empyema fluid may be
isoechoic with the liver and have no dynamic changes with respiration.
• The presence of pleural or diaphragmatic thickening or nodularity, or an
echogenic swirling pattern is suggestive of a malignant pleural effusion
[9,24,25].
• The presence of air and fluid together (ie, hemopneumothorax) may
present a complex sonographic picture.

12. Procedure

13. Procedure (contd.)

14. Post-procedure
It has been standard practice to obtain a chest x-ray after thoracentesis to
rule out pneumothorax, document the extent of fluid removal, and view
lung fields previously obscured by fluid.
Complications
• Pneumothorax
• Hemoptysis due to lung puncture
• Re-expansion pulmonary edema or hypotension (uncommon, and
probably not related to the volume of fluid removed)
• Hemothorax due to damage to intercostal vessels
• Puncture of the spleen or liver
• Vasovagal syncope
Bloody fluid that does not clot in a collecting tube indicates that blood in
the pleural space was not iatrogenic, because free blood in the pleural
space rapidly defibrinates.

15. Advantages
• Ease of use
• Highly accurate
• Documentation
• less chances of complications
• Maneuvering ability in any plane
• Real time visualisation
• Portable scanners can be used in emergeny and ICU setups
• Cost-effective
• Avaialabilty in remote and rural areas
Pitfalls
• Failure to identify the deepest pocket of fluid.
• Failure to identify the diapragm, avoiding intra-abdominal
injury.
• Failure to use this diagnostic tool for all thoracentesis
procedures.