Pleural space disease and chest taps and tubes (Proceedings)

Pleural space disease is a common cause of respiratory distress in emergent and critical patients. Air, fluid, exudates, chyle, blood, and herniated abdominal organs may be present in the thoracic cavity. When any form of space occupying condition occurs, the lungs cannot expand normally and pulmonary function fails. These patients must be stabilized first with oxygen therapy and thoracocentesis (chest tap) to improve respiratory function before diagnostics such as radiography are performed.

Respiratory trauma and thoracic wounds

Chest wounds must be investigated to ensure the pleural lining of the thorax has not been breached. "Sucking chest wounds" are penetrating wounds that lead to pneumothorax, and the name is derived from the sound of air sucking in upon inspiration. A bandage of sterile lubricating gel and sterile gauze should be placed over the area to restore a seal. Palpation of the entire chest area is necessary to find any small penetrating injuries such as bite wounds or gunshot. The presence of subcutaneous emphysema indicates a penetrating injury, skin wound, or tracheal damage. Injuries to the trachea such as crushing, laceration, avulsion, or a migrating esophageal or tracheal foreign body may not exhibit obvious external trauma. However, air leakage at the site can dissect through tissue planes causing varying degrees of subcutaneous emphysema, pneumomediastinum, or pneumothorax. A chest tap is performed to remedy pneumothorax. Wounds are cleaned and evaluated for tissue trauma, dead space, or infection. Surgical exploration of the thorax is often recommended. Tracheal wounds should be cleaned and lightly bandaged with sterile materials to minimize accumulation of subcutaneous emphysema. Intrathoracic tracheal injury would require strict cage rest and possibly surgical correction. Radiographs of the chest are taken when the patient is stable and a culture from any penetrating wound to the chest.

Pneumothorax

Blunt trauma can lead to pleural space disease. Rib fractures and flail chest often cause pneumothorax and hemothorax by lacerating lung pleura and vessels. Rib fractures are often undiagnosed until radiographs are taken. Flail chest, is often observable because of the defect it produces, and is defined as a segment of two or more adjacent ribs fractured in both a dorsal and ventral location. Segments of flail chest will move freely and paradoxically with respiration. In addition to flail chest potentially lacerating lung tissue or vessels it also negatively affects ventilatory efficiency by decreasing the amount of negative pressure (tidal volume) generated during inspiration. Likewise respiratory function is decreased due to areas of pulmonary contusion in direct proximity with rib fractures and flail segments. Pneumothorax is one of the most common results of chest trauma and occurs in roughly one quarter to one half of patients exhibiting fractures from trauma. Pneumothorax is an accumulation of free air located outside the lungs but within the chest cavity. Pneumothorax can be classified as open when accompanied by a flesh wound that communicates to the chest or closed when the leak of air occurs from within the thorax. Closed pneumothorax can be relatively minor and self-limiting when the amount of air leakage is small. Tension pneumothorax is a term used to describe severe forms of closed pneumothorax where a defect in the lung leaks air into the pleural space during inspiration and then closes during the rest of the respiratory cycle. A one-way valve is formed letting air out into the pleural space and trapping it there. Large accumulations of air inhibit lung expansion and venous return to the heart. Alveolar collapse is progressive and will result in V/Q mismatch, intrapulmonary shunting, and lung lobe atelectasis. It has been reported that dogs can tolerate up to a full tidal volume of air accumulation before lung and cardiac function become severely affected. Treatment of pneumothorax is removal of air by chest tap or chest tube placement if air repeatedly or rapidly accumulates. Rib fractures generally do not require direct treatment but patients do benefit from treatment of pain. Flail chest may require external splinting or rarely surgical fixation to limit movement of the fractured segment. Radiographs, oxygen therapy, and pain relief are all staples of diagnosis and treatment plans.

Hemothorax

Accumulation of blood in the chest may occur as a result of trauma, coagulopathy, or neoplastic conditions. Removal of the accumulated blood is not necessary unless respiratory compromise is present. Treatment of hemothorax is supportive in nature and may include fluids and blood products if the patient is hypotensive. Diagnosis and treatment of underlying disease would be most appropriate before tapping the chest of patient with a concurrent coagulopathy, provided a chest tap is not immediately needed to relieve respiratory distress.

Diaphragmatic hernia

A diaphragmatic hernia may be present from birth (congenital defect) or may occur due to traumatic injury. The blunt force of trauma causes a rent in the diaphragm and abdominal organs slide into the pleural space. The organs most commonly involved are liver, spleen, omentum, and stomach. Diagnosis is generally made upon radiographs although gut sounds may be discernable on auscultation. Treatment would be supportive in nature until surgical intervention is practical.

Pleural effusions

Pleural effusion can result from increased vascular permeability, increased hydrostatic pressure, decreased oncotic pressure, lymphatic obstruction, infection, or hemorrhage from coagulopathy or neoplasia. Specific examples of disease processes can include: congestive heart failure, cardiomyopathy, neoplasia, chylothorax (idiopathic or lymphatic obstruction), sepsis, feline infectious peritonitis, pancreatitis, hypoalbuminemia, lymphangiectasia, lymphoma, or lung lobe torsion. Evaluation of fluid sampled during chest tap may yield information as to the cause of the effusion. Measurement of total protein by refractometer will determine if the fluid is a transudate or exudate. Pleural effusions can be classified into general categories of: transudates and modified transudates, septic and non-septic exudates, chylous, hemorrhagic, or neoplastic effusions. Pure transudates are most often transparent in color and have low total protein concentration (<3gm/dl) and low nucleated cell count (<1000/ml). Cell types are typically macrophages, lymphocytes, and mesothelial cells. Decreased oncotic pressure from hypoalbuminemia (GI or renal system loss of albumin or decreased albumin production by the liver) is a common cause of a pure transudate effusion. Modified transudates may be slightly turbid in appearance and contain a slightly higher total protein concentration (up to 3.5gm/dl) and a higher nucleated cell count (up to 5000/ml). Neutrophils are a common cell type along with the above mentioned cell types. The most common cause of modified transudate effusion is increased intravascular hydostatic pressure (heart failure, pulmonary hypertension, pericardial effusion) or increased hydrostatic pressure of the lymphatics (lymphatic obstruction from neoplasia, diaphragmatic hernia, lung lobe torsion). Exudates are a result of infection, inflammation, or increased vascular permeability. Exudates are turbid in appearance and contain higher total protein concentrations (>3gm/dl) and significantly higher cell counts.

The cell types for both septic and non-septic exudates are neutrophils, macrophages, eosinophils, and lymphocytes. However septic exudates contain bacteria and extremely high cell counts (>50,000/ml) of degenerate neutrophils. It must be remembered that the absence of bacteria or other etiologic agent does not rule out infection. Culture and sensitivity and cytologic gram stain of fluid will differentiate infectious from inflammatory causes of effusion. Non-septic effusions may be caused by neoplasia, resolving sepsis, feline infectious peritonitis. Causes of septic effusions may be penetrating chest wound, bite wound, migrating tracheal or esophageal foreign body, or complication of bacterial pneumonia. Chylous effusions result from leakage of chyle from the thoracic duct. Inciting causes may be idiopathic or result from increased lymphatic hydrostatic pressure or obstruction as mentioned earlier (neoplasia, chronic diaphragmatic hernia). Idiopathic chylothorax may also result from congenital or acquired defects to the thoracic duct. Definitive diagnosis of chylothorax will be made by laboratory measurement of thoracic fluid triglyceride level (greater than serum level) and will rule out diseases causing exudative effusions. Hemorrhagic effusions appear grossly similar to frank blood, contain red blood cells, and are caused by neoplasia, trauma, or systemic coagulopathies. Packed cell volumes of chest fluid would be similar value as peripheral PCV value. Neoplastic effusions may cause any type of pleural effusion with the possible exception of a pure transudate. Diagnostic cells may or may not be present in the chest fluid. Definitive diagnosis would be made by fine needle aspiration or biopsy. Samples of thoracic fluid should be placed into EDTA blood tubes for cytologic evaluation and clot tubes for any biochemical analysis.

Pericardial effusion

Pericardial effusion is an accumulation of fluid (usually blood) within the pericardial sac. The most common causes are neoplasia, idiopathic effusion, congestive heart failure, coagulopathy, and infection. Pericardial effusion is life threatening due to the restrictive nature it has on the heart. Decreased cardiac output and systemic venous congestion result from cardiac tamponade. Thoracic ultrasound to view the heart is a very quick and non-stressful method of diagnosing the presence of pericardial effusion. Pericardiocentesis is palliative treatment that will restore cardiac output.

Chest tap equipment

For cats, a butterfly catheter 19 or 21 gauge does a very nice job with a three way stopcock and syringe attached. For an extremely obese cat, a 20 gauge 1½ inch needle may be needed. For dogs, equipment can vary from butterfly catheters, 20 gauge 1½ inch needles, or 20 gauge over the needle peripheral catheters. Any of these would be appropriate for smaller sized dogs (<15kg). For larger dogs 16 or 18 gauge catheters are often used. Thoracic drainage catheters work well for all but the smallest of dogs and will be discussed separately.

Pros and cons exist for any instrument chosen but all are generally safe if used in an appropriate manner. Butterfly catheters and 20 gauge needles have the sharp end that will remain in the chest during evacuation. To prevent lung laceration, the tip of the needle should be angled closer to the chest wall. As greater volumes are removed, angle the needle parallel with the internal chest wall. Peripheral catheters do not risk lung laceration once the stylet is removed; however these catheters kink very easily between layers of skin, intercostal muscle, and pleura making drainage impossible. Typically this means several more punctures the patient has to endure. Regardless of instrument chosen to perform the tap, an extension set with 3-way stopcock facilitates rapid evacuation and minimizes trauma caused by movement.

Chest tap procedure: Clip at least a 4" square area over the 7-10th intercostal space. Air will be removed easiest from the dorsal third of the chest, and the patient can be in sternal or lateral recumbency. Ventral taps will remove the most fluid with the patient in sternal recumbency or standing. An initial scrub of the skin is performed. Local anesthesia of lidocaine or bupivicaine in the skin and intercostal muscles can be helpful. Another complete scrub of the skin is performed. Sterile gloves are worn to guard against infection.

Identify the 7-8th or 8-9th intercostal space. Grip close to the tip to ensure the amount of penetration into the chest does not exceed what is necessary or safe. Puncture into the chest on the cranial aspect of a rib. If rib is struck while advancing the needle, the needle must be "walked" off the cranial side to avoid the intercostal arteries, veins, and nerves that run along the caudal curvature. Once inside the pleural space, the extension set is connected as quickly as possible or a sterile finger is used to plug the needle or catheter decreasing the chance of air entering. An assistant will hold the syringe and aspirate as the needle is advanced in small increments, and they can indicate whether each aspiration is negative (receives negative pressure) or yields air or fluid. With the extension set, 3-way stopcock, and syringe system attached anything evacuated from the chest can be quickly expelled. After aspirating a full syringe, the stopcock is closed to the patient and the air or fluid is pushed out. The 3-way is then turned off to the open port and evacuation is resumed.

Thoracic drainage catheters (CookРVeterinary Products)

For cats a drainage catheter would only be used for instances when the catheter would be left as an indwelling chest tube. Otherwise, the size of the drainage catheter is too large. An 8fr. drainage catheter would be appropriate in those indwelling situations. Small canine patients would also benefit from the smaller 8fr. size catheter. A 10fr. is appropriate for medium and large dogs (weighing >15kg). For evacuation of large volumes, drainage catheters perform superiorly whereas other peripheral catheters or needles may drain only small volumes and need to be repeated on both sides of the chest. Placement of a drainage catheter is usually sufficient to completely drain the entire chest. This is a big advantage for the patient to receive only one needle puncture. Disadvantages of the thoracic drainage catheter are price and size.

Drainage catheter placement procedure

As a rule, most every patient should receive sedation, analgesia, and local anesthesia. Clip a large area of the chest (rib spaces 4-13). An initial scrub of the skin is performed. Infiltrate skin and muscles with local anesthetic. Sterile gloves are worn and a drape is placed over the site. A full thickness stab incision through the skin is made with a number 11 or 15 scalpel blade. Intercostal rib spaces 7-8, 8-9, or 9-10 are appropriate. Before beginning, make certain the catheter is not adhered to the stylet by removing the catheter from the stylet and then replacing it. Hold the catheter with the non-dominant hand wrapped firmly around the catheter approximately 1 ½" from the trocar tip. This will ensure the chest is not penetrated too far. The dominant hand is used on the driving end and the catheter is held perpendicular to the chest. Once the thoracic cavity is entered the catheter is aimed toward the patient's opposite elbow. Next the stylet is quickly unscrewed and the catheter is advanced off the stylet into the chest.

These catheters have multiple perforations that must be placed inside the chest very quickly in order to avoid a pneumothorax. Fluid can also leak out of these fenestrations once the tip is inside the chest. In general, more length of the catheter is fed into the chest initially than may be needed. The catheter can be backed out if placed too far cranial inside the chest. But due to risk of contamination, advancing the catheter further into the chest at a later time is never allowed. Radiographs would be indicated if the catheter will be indwelling. The end of a drainage catheter has a female connector to connect with an extension set, 3way stopcock, and syringe. Once aspiration of the chest is finished, the catheter is removed with a quick, continuous, pull while the skin is pinched around the catheter at the insertion site. Fingertip pressure is maintained for several minutes, and a light bandage using a triple antibiotic ointment applied. If preferred, a skin staple could be placed at the insertion site.

Chest tubes

A size 10 or 12fr. (ArgyleЩ chest tube is appropriate for most cats and small

dogs while medium and large dogs need a 20 or 28fr. tube. Connecting adapters, suction tubing, and tube occluding clamps need to be ready before placement. The size of the tubing and adapters will be dependant on the size of the chest tube. Consideration needs to be given whether the patient will be placed on continuous underwater drainage. A three way stopcock may be necessary in the connections in order to infiltrate the pleural space with local anesthetic or flush the chest with sterile saline. Only three way stopcocks with leur lock fittings should be used. A chest tube clamp can be made from a straight hemostat with lengths of red rubber catheters cut to fit over each jaw. Tube occluding clamps can also be purchased. Placement of an indwelling chest tube is indicated to remove recurring air, large recurring volumes of fluid, or to lavage the chest. A commonly accepted guideline requires chest tube placement if three chest taps are needed within 24 hours or if a pneumothorax is very rapidly recurring. Placing these tubes is very similar to placing a thoracic drainage catheter.

Chest tube placement procedure

With the anesthetized patient in lateral recumbency, clip and prep an area from the scapula to well past the last rib closely approaching the spine and the sternum. An assistant pulls the patient's skin cranial ventral as far as possible and holds it until placement of the tube into the chest. When this pulled skin is released, it will provide a tunneled space guarding against air communication. The 9-10 intercostal space is identified and a skin incision is made in the dorsal third of the chest.

Blunt dissection is performed with hemostats through the subcutaneous fat and the intercostal muscles. Before placement, the chest tube is measured from the last rib to the elbow to approximate the length of tube to be placed inside the chest. The trocar end of the tube is held with the dominant hand approximately 1 ½ -2" from the tip while the non-dominant hand is on driving end of the tube. The tube is directed perpendicularly until the pleural space is entered and then aimed toward the opposite (down) elbow. The tube and stylet is advanced together only until it has entered the thorax. The chest tube is then quickly advanced into the chest while the stylet is held in place. Once the chest is penetrated the anesthetist must provide controlled ventilation to avoid a pneumothorax. The stylet is removed and the chest can be evacuated using sterile connections and an occluding clamp can be applied to the tube. A purse string suture is placed in the skin, and a finger trap suture is used to hold the tube in place.

Once the chest tube is secured, a light sterile wrap is applied. Radiographs are obtained while the patient is still anesthetized to confirm correct placement of the tube. Connections should be placed to utilize either intermittent or continuous suctioning, and secured to insure that all seals are air tight. Suture, wire suture, tape, or thin strips of adhesive dressing can be used to secure various connections. Sterile gauze and triple antibiotic ointment at the insertion site provide the first layer of bandage. Kling and Elastikon work nicely for a secure bandage. Always remember to tape a loop of the tubing to the bandage so the patient cannot pull directly on the insertion site.

References available on request