Julie Menard DVM, Dipl. ACVECC and Tomas Boullhesen Williams DVM

Thoracocentesis

Thoracocentesis is indicated when pleural space disease (e.g., pleural effusion, pneumothorax) is suspected and/or diagnosed based on physical examination and/or Point-of-Care ultrasonography (POCUS). Air and fluid can accumulate within the pleural space, causing pneumothorax or pleural effusion, respectively. This impairs ventilation and oxygenation, leading to respiratory distress, pain, hypoventilation, and hypoxemia. Thoracocentesis should be performed before attempting to obtain thoracic radiographs in unstable cats.

Thoracocentesis has both diagnostic and therapeutic purposes. Diagnostic thoracocentesis helps identify the nature of the problem and tailor therapy and prognosis. When effusion is sampled, measurement of total solids via refractometry and in-house cytology using Romanowsky-type quick staining (e.g., Diff-Quik) should be performed. In case of suspected pyothorax, aspirated pleural fluid should be placed in culture media and stored at room temperature until submission for microbiological culture and susceptibility. Therapeutic thoracocentesis is performed to alleviate abnormal pressure within the pleural space and is recommended prior to performing radiography to increase chances of identification of intrathoracic pathology. 

Flow-by oxygen should be administered to all patients undergoing thoracocentesis.  Electrocardiography monitoring is recommended. Thoracocentesis is well tolerated with only mild sedation (table 95.1).

Cats are typically placed in sternal recumbency with minimal restraint to limit stress. Ideally, the smallest gauge peripheral catheter or needle should be used as shown in fig. 95.1.  

Usually a 22G needle is sufficient, although a larger gauge may be necessary for high viscosity fluids (e.g., pyothorax, FIP effusion). Needle length depends on the cat’s body fat, but usually a ¾ inch (0.3 cm) needle is sufficient. Complications related to thoracocentesis include laceration of the intercostal neurovascular bundle, pain, and iatrogenic pneumothorax. 

Thoracostomy tube placement 

Chest tube placement is indicated for removal of air or fluid from the pleural space to alleviate pulmonary collapse and allow normal breathing. The authors recommend thoracostomy tube placement for treatment of pyothorax or after repeated thoracocentesis (3 times or more) has failed to alleviate clinical signs or in the case of a tension pneumothorax when negative pressure is unable to be achieved.  

There are two main types of chest tubes; large-bore tubes (e.g., trocar type tubes, >14 French diameter) and small-bore tubes (<14 French diameter) that are placed using the Seldinger technique.¹ Human studies report a lower number of complications when using small-bore tubes.² There are no studies in veterinary medicine comparing the complication rates for tube types, but small-bore catheters were shown to be safe and effective.³ A veterinary study showed both small- and large-bore tubes had similar efficacy for removing known amounts of air, as well as low and high viscosity fluid from the pleural space of canine cadavers.⁴ Table 95.2 compares the two different types of chest tubes. Flow-by oxygen and electrocardiographic monitoring is recommended for the procedure. Placement of small bore tube with Seldinger technique is shown in video 95.1

Once proper placement of the chest tube is confirmed, the tube should be covered with sterile materials. The patient should always wear an Elizabethan Collar when the tube is in place, and strict monitoring of the patient is recommended to avoid accidental tube removal by the patient. Strict sterile technique is required when manipulating the chest tube, and the patient should be housed on clean bedding at all times. Multimodal analgesia should be provided to the patient while the chest tube is present (table 95.3).

The complication rate associated with the use of small-bore chest tubes is unknown. Some reported complications are pneumothorax, infection, lung trauma, arrhythmias, incorrect placement, drain occlusions, hemorrhage from intercostal vessel rupture, inadvertent removal, and fluid leakage around the catheter.³ Once the chest tube is removed, the incision can be closed using sterile suture or skin staples.

References

1. Boysen SR. Chest tubes part 1: types and indications. Companion Anim 20:488-492, 2015.

2. Contou D, Razazi K, Katsahian S, Maitre B, Mekontso-Dessap A, Brun-Buisson C, et al. Small-bore catheter versus chest tube drainage for pneumothorax. Am J Emerg Med 30:1407-1413, 2012.

3. Valtolina C, Adamantos S. Evaluation of small-bore wire-guided chest drains for management of pleural space disease. J Small Anim Pract 50:290-297, 2009.

4. Fetzer TJ, Walker JM, Bach JF. Comparison of the efficacy of small and large-bore thoracostomy tubes for pleural space evacuation in canine cadavers. J Vet Emerg Crit Care 27:301-306, 2017.