Thoracocentesis is the aspiration of air or fluid from the pleural space. The purpose of this invasive clinical technique may be diagnostic and/or therapeutic. Thoracocentesis or “chest tap” allows characterization of the fluid type and determination of the possible underlying cause. Thoracocentesis is also used to relieve respiratory distress seen with marked effusion or severe pneumothorax. Significant pleural effusion is often associated with shallow and rapid breathing in the ferret. In some cases, open-mouth breathing or coughing is also observed. Reduced breath sounds are ausculted.
- Butterfly catheter or over-the-needle catheter, 20-25 gauge, ¾ inch (select the smallest needle possible)
- Three-way stopcock
- 6-12 cc syringe
- Sterile gloves
- Antiseptic scrub and alcohol
- Collection tubes (sterile and EDTA), culturettes, and glass slides for cytology, fluid analysis, culture, and sensitivity
- ±General anesthesia or sedative
- ±Supplemental oxygen
- An endotracheal tube, bright light source, and emergency drugs should also be available when performing any procedure in a critically ill, dyspneic ferret.
Thoracocentesis is ideally a three person procedure. One person restrains the conscious animal or monitors the anesthetized patient. A second person holds the needle steady while a third person works the stopcock and aspirates fluid or air.
Although anatomy of the ferret makes thoracocentesis more difficult than in cats and dogs, complications are rare.
- The most common complication is mild pneumothorax.
- Lung laceration may cause hemorrhage and/or pneumothorax.
- Laceration of the internal thoracic artery or an intercostal vessel may also cause iatrogenic hemothorax.
- Neuritis, and/or paralysis of intercostals muscles may develop secondary to damage to intercostal nerves.
- In rare instances, the heart, liver or stomach may be punctured during thoracocentesis.
Site for thoracocentesis
- It is usually necessary to use chest radiographs or ultrasound as a guide to choose the proper site for needle insertion in the ferret (Fig 1).
- Clip fur from the sixth to tenth ribs on both sides.
- Ferrets have 14 ribs instead of the 13 ribs found in dogs and cats. The heart sits in a relatively caudal location, extending from the sixth rib to the caudal border of the seventh or eight rib with the apex only 1 cm from the diaphragm (Fig 2).
- Provide supplemental oxygen beforehand as needed.
- Meanwhile attach the butterfly catheter to a 3-way stopcock and syringe. Check all connections for leakage, and place the stopcock in an “off” position.
- Unless the patient is moribund, provide general inhalant anesthesia or sedation.
- Deliver isoflurane or sevoflurane via facemask.
- Sedate the patient with butorphanol (0.2-0.4 mg/kg IM), midazolam (0.3-0.5 mg/kg IM, SC ) or
ketamine (10-20 mg/kg IM ) combined with diazepam (1-2 mg/kg IM).
- Prepare the site by clipping fur from the 6th to 10th ribs on both sides (see above).
- Place the animal in lateral or sternal recumbency.
- Aseptically prepare the site using antiseptic scrub and alcohol.
- Insert the needle at an oblique angle with the bevel pointed dorsally. Insert the needle along the cranial border of the ribs to avoid laceration of vessels and nerves that run along the caudal aspect of the ribs. Insert the needle at the junction of the mid to dorsal third of the thorax for pneumothorax. Insert the needle into the ventral third of the chest for pleural effusion.
- Pass the needle through the skin and advance it slowly into the pleural space. A slight pop may be felt when the needle enters the pleural space. Resistance to needle passage also decreases.
- After the needle has entered pleural space, align the needle so it is parallel to the body wall.
- Open the stopcock and gently aspirate fluid or air. Approximately 6 ml of fluid is sufficient for diagnostic procedures. Continue aspiration until negative pressure is reached if the chest tap is performed to relieve dyspnea.
- Repeat the procedure on the hemithorax as needed.
- To prevent reaccumulation of fluid, treatment must be based on a definitive diagnosis (Table 1). Transfer the sample collected to EDTA tubes for fluid analysis. Use sterile tubes and culturettes for aerobic and anaerobic culture and sensitivity. For cytologic analysis, stain air-dried glass slides with Diff-Quick.
A negative tap suggests solid pleural space disease such as a mass lesion, abscess, hernia, or primary cardiac or pulmonary disease.
Table 1. Fluid analysis and cytology of effusions
|Transudate||Modified transudate||Exudate, Non-septic||Exudate, Septic||Chyle||Hemorrhage|
|Turbidity||Clear||May be slightly butty||Butty, fibrin may be present||Butty||Opaque||Spun supernatant clear|
|Color||Colorless to pale yellow||Yellow or pink||Yellow or pink||Yellow to red-brown||Milky white||Red|
|Cells/mm3||<1,000||1,000-7,000||5,000-20,000 (up to 100,000 with lymphoma)||5,000-300,000||1,000-20,000||Consistent with peripheral blood|
|Predominate cell type(s)||Mostly mesothelial cells||Macrophage, mesothelial cell predominates; few non-degenerate neutrophils, erythrocytes, and lymphocytes, may contain neoplastic cells||Non-degenerate neutrophils and macrophages (lymphocyts and neoplastic cells may be seen)||Degenerate neutrophils and macrophages||Neutrophils, lymphocytes, macrophages||May see macrophages with erythrophagocytosis; does not clot|
|Differential diagnoses (Rare differentials are listed in parentheses)||Early congestive heart failure, hypoalbuminemia||Congestive heart failure, neoplasia such as mediastinal lymphoma or thymoma||Neoplasia such as lymphoma, (Aleutian disease virus, diagphragmatic hernia)||Pyothorax (bite wounds, migrating inhaled foreign body, pneumonia or pleuropneumonia, lung abscess)||Heart failure, neoplasia such as lymphoma, trauma, (cranial vena cava obstruction, fungal disease, diaphragmatic hernia)||Neoplasia such as lymphoma, trauma, coagulopathy|
After the chest tap, obtain survey chest radiographs and possibly an echocardiogram to better evaluate the ferret’s underlying pathology. Most patients undergoing thoracocentesis are hospitalized because they require intensive care. Monitor the patient closely for return of dyspnea by checking the respiratory rate and ausculting the ferret regularly.