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thoracocentesis is the name given to a clinical technique whereby fluid or air is removed from the thoracic cavity.
indications for use
* emergency removal of air/fluid from the thoracic cavity - their presence causes dyspnoea and this must be eased to assist the animal in ventilating its lungs and hence oxygenating the blood.
* analysis of fluid - the type of fluid removed from the thorax can be a valuable diagnostic aid:
milky fluid- probably chyle, it indicates rupture of the thoracic duct within the thorax. this condition is called chylothorax.
bloody- blood removed from the thorax is a sign of crushing of the great vessels and is often a sequel to a crushing injury such as road traffic injury. this is called haemothorax.
if air is removed from the thorax the condition is called pneumothorax. this can be due to many things, an example of which is a penetrating wound to the thorax.
* improved radiographs - pleural fluid can be seen on a radiograph and is common to many diseases. analysis of the fluid allow more accurate diagnosis to be made. since fluid is radiodense it may obscure pathological changes within the mediastinum. removal of the fluid will hence allow better radigraphs to be made.this can be split into two broad categories-
insertion of the needle
the position in which the needle is inserted depends on whether there is air or fluid present but the basic technique is the same.
* the needle is inserted into the middle of the correct intercostal space, this is done to avoid the blood vessels and nerves that run down the caudal edge of each rib.
* aseptic conditions must be obeyed strictly and the operator should wear sterile gloves. this avoids the iatrogenic introduction of an infection into the pleural space.
* the needle is inserted at a 45" angle towards the parietal pleura preventing the lung parenchyma from obscuring the needle lumen when aspiration is being performed.
* the animal should be standing if possible but if not the animal should be in lateral or sternal recumbency.
* if the animal coughs, struggles or shows signs of discomfort during the technique the needle should be withdrawn or directed.
* gentle negative pressure should be applied as you enter the pleural space.
* as soon as you enter the pleural space stop and hold the needle/syringe parallel to the body wall with the tip pointing ventrally. this reduces the risk of lung laceration.
* the needle should be inserted in two steps. firstly, the needle should be inserted through the superficial fascia, integument and muscle. secondly, the needle should be moved dorsally or ventrally about 1cm and then inserted through the rest of the muscle and the parietal pleura. this is done so that when the needle is removed the two holes caused by the needle are not aligned reducing the risk of a pneumothorax. * if the fluid/air is difficult to get the needle should be withdrawn slightly, before redirecting the tip. alternatively, the other side of the thorax can be used.
* local anaesthetic is not normally used but is useful if large volumes of fluid are to be removed.
* since the size of the lung is reduced during expiration, if possible insert the needle when the animal is expiring.
to remove fluid:
* in the dog thoracocentesis is performed in the ventral third of the thorax and the 6th-8th intercostal spaces. this is because the needle will go into one of the pleural recesses reducing the risk of lung laceration and will pass cranial to the costodiaphragmatic line hence entering the thorax rather than the abdomen!
* although the position of insertion of the domestic species is not given, an appreciation of the sections on the anatomy of the pleura and lungs will allow the operator to do it safely.
* this is because as with the dog the operator should aim to insert the needle cranial to the costodiaphragmatic line, caudal to the basal border of the lung and within the ventral third of the thorax.
to remove air:
* this is also done in the 6th-8th intercostal spaces but at the highest point of the thorax.
* this will vary depending on the position the animal is in during the technique.
* standing or sternally recumbent- dorsal third of the thorax.
* laterally recumbent- mid thorax.
