Thoracocentesis

Introduction

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

When the findings from either thoracic auscultation or percussion suggest a pleural effusion, thoracocentesis can both confirm its presence and provide a specimen for examination. Drainage of pleural effusion via thoracocentesis is beneficial in removing large volumes of fluid from the thorax. Immediately following this drainage, some horses show increased pain, associated with loss of the ‘cushion’ of fluid in the pleural space. Removal of this fluid decreases respiratory effort and is beneficial in the resolution of an infectious process in the thorax. In horses with thoracic neoplasia and large volumes of pleural effusion, thoracocentesis and chest drainage may resolve signs of dyspnoea and respiratory distress.

Equipment

• 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

Procedure

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

Complications

Pneumothorax

Peritoneal 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 from healthy horses may contain up to 10,000 nucleated cells/l and 35g/l total protein. Most horses have less than 5,000 nucleated cells/l and less than 25g/l total protein.

References

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

add electives reference and in practise reference.