Dr. Mazzaferro is a critical care specialist and an author of Handbook of Veterinary Procedures.
Blunt or penetrating trauma is the most common cause of pneumothorax; however, spontaneous pneumothorax also can occur. Other causes of pneumothorax that have been documented include barotraumas secondary to anesthetic equipment malfunction, tracheal rupture, or secondary to dirofilariasis.
Clinical signs of pneumothorax include respiratory distress, tachypnea, open-mouthed breathing, cyanosis or pale pink- to-gray mucous membranes, and a rapid shallow restrictive respiratory pattern. Pneumothorax should be considered in any patient with known trauma. However, the clinical signs associated with pneumothorax are not pathognomonic, and are also observed with other pleural space problems, including pleural effusion, pulmonary contusions, and diaphragmatic hernia. Auscultation of the thorax in all cases will reveal muffled heart and lung sounds. Thoracocentesis, in all cases, can be both therapeutic as well as diagnostic.
Emergency treatment in patients displaying signs of pneumothorax or restrictive respiratory pattern includes immediate oxygen supplementation in the form of flow-by oxygen. A therapeutic and diagnostic thoracocentesis should be performed to relieve respiratory distress and stabilize the patient before any radiographs are performed. Analgesia and sedation may be required to alleviate stress of breathing, anxiety, and pain.
Radiographs should be performed only after the patient's respiratory and cardiovascular system have been stabilized. Oxygen therapy, therapeutic thoracocentesis, and intravenous fluids for vascular support are necessary before subjecting the patient to radiographs. Following successful stabilization, radiographs can be performed to evaluate the patient for continued air accumulation, rib fractures, or diaphragmatic hernia.
When pneumothorax occurs secondary to trauma, other injuries that are often concurrently observed are pulmonary contusions, rib fractures or flail chest, and diaphragmatic hernia. Penetrating wounds into the thorax may also be associated with hemothorax and vessel laceration, myocardial contusion or hemorrhage, and the presence of foreign bodies.
A tension pneumothorax occurs when intrapleural pressure exceeds atmospheric pressure resulting from a one-way flap valve in either an airway (bronchopleural fistula) or the chest wall (pleurocutaneous fistula). The alternate opening and closing of the valve allows the negative intrapleural pressure during inspiration to aspirate air into the pleural cavity. The air cannot leave during expiration due to closing of the one-way valve. Once the rise in intrapleural pressure exceeds atmospheric pressure, the tension pneumothorax is rapidly progressive and fatal if not treated.
In any patient with pneumothorax, diagnostic and/or therapeutic thoracocentesis is the mainstay of therapy. A square section of fur should be clipped from each side of the thorax. Each area is quickly aseptically prepared. Next, a 1-inch 18–20-gauge needle should be inserted in the mid thorax between the 7th–10th intercostal space, carefully avoiding the caudal border of each rib. Once the needle is inserted into the pleural space, the needle should be placed parallel with the thoracic wall to avoid penetrating the lung parenchyma. A piece of IV extension tubing should be attached to the hub of the needle at one, and a three-way stopcock at the other end. Finally, a 60-ml syringe is connected to the three-way stopcock and slowly aspirated for air or fluid. If negative pressure is observed, the needle should be re-directed in several spots, as pockets of air may restrict breathing and cause lung collapse. Once negative pressure is obtained, the entire procedure should be repeated on the other side of the thorax.
Continued accumulation of free air within the pleural space that is refractory to therapeutic thoracocentesis requires placement of a chest tube. Placement of the chest tube should be performed in a way that minimizes stress. One mcg/kg intravenous bolus of fentanyl or 2–4 mg/kg IV Propofol can be used for sedation and chemical restraint. The skin should be aseptically prepared on the side of the thorax generating the most free air. Local anesthetic (0.75 mg/kg 2% lidocaine) is then infused near the proximal 10th intercostal space and directed cranioventrally such that the chest tube will enter the mid-thorax between the 7th–9th intercostal space. Following local anesthetic infusion, a 8–10 Fr trocharized tube can be placed. A stab incision is made with a scalpel blade at the proximal 10th intercostal space, and the tube tunneled under the skin to the 7th–9th intercostal space. An assistant can pull the skin cranioventrally to aid tunneling. Next, the thorax should be compressed over the sternum to increase intrathoracic pressure while placing the trochar through the body wall. Once the trochar enters the pleural space, the tube should be pushed off of the trochar in a cranial-ventral direction. The tip should lie at approximately the 3rd intercostal space, just cranial to the heart. Christmas tree adapter, connected to extension tubing, three-way stopcock and 60-mL syringe is connected to the chest tube and immediate suctioning should be performed. The chest tube is then secured with a horizontal mattress suture around the tube. A second purse string suture is placed in the skin at the tubes entrance point, then further secured with a Chinese finger trap. The chest tube can then be intermittently suctioned every hour or more frequently as needed, or connected to a Pleur-evac continuous suction system. 0.75 mg/kg lidocaine, followed by 0.75 mg/kg bupivacaine can be flushed into the chest tube three times daily to alleviate patient discomfort.
If a trocharized tube is not available, an alternate method of placement can be implemented. A red rubber tube can be clamped in the distal tips of a Rochester-Carmalt. The Carmalt is placed through the stab incision in the skin and tunneled as with the trochar. With blunt force, the tips of the Carmalt are inserted through the chest wall at the 7th intercostal space. The red rubber tube is then inserted into the pleural cavity and directed cranially and ventrally to the 3rd intercostal space. The wide end of the tube is attached to the Christmas tree adapter and suctioning apparatus to facilitate evacuation of the thorax.
References are available upon request.