USG Guided Thoracentesis

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USG GUIDED THORACENTESIS

• Dr.Suhas B
• Resident
• (MD Radio-Diagnosis)

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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)
• Diagnostic evaluation of pleural fluid

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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 hyperechoic or
  tissue dense and, in large effusions, may appear
  to float in the effusion.

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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.

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• 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

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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 patients 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.
• Same should be done for the transducer and should
  be sterilised following its use each and
  everytime.

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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.

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• Pleural effusion with rib shadow. The
  transducer is placed perpendicular to the axis of
  the rib.

• Muscle, fluid, lung, and measurements.

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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.

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Procedure
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Procedure (contd.)
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• 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.

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• 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.
• Not appreciating that the lung is a moving
  structure. This may change the depth of fluid
  with in-or expiration.

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Thank You