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Also known as: Pleurocentesis

Equine Thoracocentesis


Thoracocentesis is a valuable diagnostic and therapeutic procedure.

When the findings of thoracic auscultation or percussion are suggestive of pleural effusion, thoracocentesis can be performed to:

  • Confirm the presence of pleural effusion
  • Provide a specimen for examination which provide a diagnosis or guide the therapeutic plan
  • Therapeautically drain a large volume of pleural fluid

The horse may show more discomfort if a significant amount of fluid is drained because the fluid had previously provided a 'cushion' effect in the pleural cavity. However the removal of this fluid is beneficial as it relieves dyspnoea and removes infectious material from the pleural space, which aids resolution. The placement of chest drains following thoracocentesis may be necessary in cases of thoracic neoplasia and severe pleural effusion.


  • Sedation as necessary
  • Clippers and materials to perform a surgical scrub
  • Ultrasonography if available
  • Local anaesthetic and a 23G 3cm needle
  • Sterile gloves
  • Number 15 scalpel blade
  • Cannula, 3-way tap and extension set
  • EDTA tube, plain tube and sterile vial for culture


The site for thoracocentesis can be identified using anatomical landmarks; 7-8th intercostal space on the left or 6-7th intercostal space on the right midway between the shoulder and the elbow. For more reliable identification of the correct position for thoracocentesis ultrasound can be used. As there are vessels and nerves running along the caudal aspect of each rib, the cannula should aim for the cranial border of the rib in order to avoid damage to these structures.

The horse should be sedated and the area clipped and scrubbed. Local anaesthetic should be administered into the subcutis, intercostal musculature and parietal pleura using a 23 gauge, 3 cm needle. A stab incision using a number 15 scalpel blade should be made through the skin. Prior to inserting the cannula, a three-way tap and extension set should be attached to it. Using moderate pressure, the cannula should be pushed through first the intercostal muscles and secondly through the parietal pleura in order to enter the thoracic cavity. Passage of the cannula through the parietal pleura is extremely painful to the horse if the area has not been fully desensitised by the local anaesthetic. A release in pressure should be felt when the cannula enters the thoracic cavity. The cannula can be manipulated and moved to collect as much fluid as possible.


Iatrogenic pneumothorax

Pleural Fluid Analysis

Analysis of the pleural fluid may in turn help you to determine the underlying disease process and develop a therapeutic plan.

Pleural fluid in healthy horses normally contains less than 5,000 nucleated cells/l and less than 25g/l total protein. Levels greater than 10,000 nucleated cells/l and 35g/l total protein should be considered abnormal.

Small Animal Thoracocentesis


Thoracocentesis is a procedure which has both diagnostic and therapeutic value.

When the clinical history, presenting signs, thoracic auscultation and percussion of the animal suggest a pleural effusion, thoracocentesis can both confirm its presence and provide a specimen for examination. Ideally radiography (minimum of two views - lateral and dorsoventral) or ultrasound should be performed to confirm pleural space disease prior to thoracocentesis. However it can be particularly useful in the emergency patient (the dyspnoeic cat in particular) who is too unstable to undergo radiography or similar diagnostic tests as drainage of pleural fluid will both provide a preliminary diagnosis and improve clinical signs.


  • Clippers and materials to perform a surgical scrub
  • Ultrasonography if available
  • Sterile gloves
  • Butterfly needle with incorporated extension set or sterile needle (1 inch with the smallest possible gauge) with extension set
  • 20ml sterile syringe
  • 3-way tap - if large volumes of fluid are anticipated, as this allows for multiple syringes of fluid to be removed safely under a closed system
  • EDTA tube for cytology and plain tube for biochemistry and culture

Sedation is not generally required, especially in the dyspnoeic patient (however it can be used if necessary to prevent further stress to an excitable animal). The patient should be handled gently and the procedure performed in a quiet environment. It may be necessary to place the animal in an oxygen cage prior to the procedure as they often have a poor oxygen reserve.


The site for thoracocentesis is between the 7th and 8th intercostal space. If fluid is suspected in the pleural space then the needle should be inserted 2/3rds of the way down the chest. If pneumothorax is suspected then the needle should be inserted more dorsally, approximately 1/3rd of the way down the chest. Local anaesthetic can be used if necessary.

Clip and scrub a generous area around the 7-8th rib space on both sides of the chest. Advance the needle slowly at a 45 degree angle in the middle of the 7th or 8th intercostal space into the pleural space. A small amount of negative pressure should be applied as the needle passes through the thoracic wall. The needle should be angled downward, parallel to the body wall. The fluid or air should then be aspirated. The needle may need redirecting to access pockets of fluid.

Up to 100mls of fluid per side can be expected in the cat. Removal of fluid should see an improvement in clinical signs.


Iatrogenic pneumothorax

Pleural Fluid Analysis

Analysis of the pleural fluid may in turn help you to determine the underlying disease process and develop a therapeutic plan. The following can be analysed: cytology, total cell count, differential cell count, total protein, bacterial culture ans sensitivity, gram stain and triglyceride and cholesterol levels (if chylothorax is suspected).

The types of fluid that may cause pleural space disease are:

  1. Exudate
  2. Modified Transudate
  3. Transudate
  4. Chyle

These can be identified by the protein and cellular content of the sample.

The fluid can give an indication of prognosis; in the cat prognosis is generally poor for all diagnoses except pyothorax (an exudate with degenerate neutrophils and intracellular bacteria). Therefore it is often useful to perform in-house cytology to give a preliminary diagnosis, which allows the owners to make an informed decision before proceeding with further treatment. Differential diagnosis in the cat include congestive heart failure, FIP, pyothorax, neoplasia, haemothorax and chylothorax. It should be noted that any pleural effusion may produce bizarre mesothelial cells which could be mistaken for neoplastic cells.

Thoracocentesis Learning Resources
FlashcardsFlashcards logo.png
Test your knowledge using flashcard type questions
Equine Internal Medicine Q&A 18
Equine Internal Medicine Q&A 19
Cytology Q&A 03
Small Animal Emergency and Critical Care Medicine Q&A 03


Adamantos, S (2011) Feline Respiratory Emergencies RVC Emergency Medicine and Critical Care Elective, Royal Veterinary College

Mair, TS & Divers, TJ (1997) Self-Assessment Colour Review Equine Internal Medicine Manson Publishing Ltd

RVC staff (2009) Respiratory System RVC Intergrated BVetMed Course, Royal Veterinary College

Rutgers, C H (1989) Thoracocentisis in the dog and cat In Practice 1989 11: 14-1

Copas, V (2011) Diagnosis and treatment of equine pleuropneumonia In Practice 2011;33:155-162

RVC staff (2011) A logical approach to clinical problem solving RVC Feline Medicine Elective, Royal Veterinary College

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