Thoracic surgery (part I) (Proceedings)

Surgical approaches

The choice of surgical approach depends largely on the type of access needed for the thoracic surgery. Intercostal thoracotomy and median sternotomy are the two most commonly performed approaches in small animals. Be certain to clip and prepare a large enough area to anticipate placement of a thoracostomy tube and the potential need to extend the incision.

Intercostal thoracotomy

Use this approach to expose a specific region of a hemithorax. Intercostal thoracotomy provides good access to the hilar area of the lungs and the heart. Additionally, exposure of the mediastinum and a portion of the ipsilateral thoracic cavity is achieved. Spaces available for performing an intercostal thoracotomy are the third through the tenth, although the fourth through the sixth intercostal spaces are more frequently entered.

Use the lateral thoracic radiograph to help determine the appropriate intercostal space to incise. Remember that when performing a lung lobectomy, center the approach over the hilus of the lung not over the lesion (cranial lobe - 4th or 5th, middle lobe - 5th, caudal lobe - 6th intercostal space). Use a 4th intercostal thoracotomy incision (5th in the cat) to expose the heart in the dog. Use the 8th intercostal space to expose the caudal esophagus.

Incise the skin parallel to the ribs and have the incision extend from just ventral to the costovertebral junction to just dorsal to the sternum. Incise the latissimus dorsi muscle with scissors parallel to the skin incision. Verify intercostal space identification by counting caudally from the first rib. Incise the serratus ventralis muscle parallel to its fibers to expose the desired intercostal space. Incise the intercostal muscles midway between ribs to avoid the intercostal vessels and nerve. Bluntly puncture the pleura to allow the lungs to fall away from the lateral thoracic wall before extending the intercostal incision with Mayo scissors. The intercostal muscle incision should extend ventral to the costochondral junction to assure adequate exposure. Insert rib retractorsa over laparotomy sponges to protect skin and muscle.

Place a thoracostomy tube as described below. Close the intercostal space by placing heavy (usually 0 or #1 suture) absorbable sutures (polydioxanone or polyglyconate) circumcostally to appose the ribs. Pre-place these sutures to help avoid traumatizing adjacent structures. Close the serratus ventralis and scalenus muscles as a separate layer. Close the latissimus dorsi muscle separately with a simple continuous pattern of absorbable material incorporating the fascia as much as possible. Close the subcutaneous tissue and cutaneous trunci muscle together. Close the skin in routine fashion.

Median sternotomy

This approach allows access to the entire thoracic cavity. It is indicated when exploration of both sides of the thoracic cavity is necessary. Structures in the dorsal thoracic cavity (e.g., hilus of lung lobes) are more difficult to reach through this approach. Median sternotomy can be combined with a ventral midline celiotomy or a caudal cervical approach, if more exposure is needed. Exposing cranial or caudal mediastinal masses and performing a more complete subtotal pericardiectomy is enhanced through a median sternotomy compared to a lateral thoracotomy. Avoid incising the entire length of the sternum, as postoperative sternal instability and pain seem to be increased compared to leaving at least one sternebra intact at either end.

Incise the skin and subcutaneous tissues over the sternum with a scalpel. Incise the pectoral muscles with scalpel to expose the sternebrae. Cut the sternum on midline with an oscillating saw, taking care to limit penetration of the saw blade. Use the handle of a spay hook to protect underlying tissues once the thoracic cavity is entered. Protect the tissues with moistened laparotomy sponges, and position retractorsa to achieve adequate visualization.

Place a thoracostomy tube prior to closing the incision. Close the sternal incision by placing stainless steel wire (approximately 20 gauge) in a figure-eight pattern to appose each incised sternebra. Pre-place these sutures to aid visualization. Close the pectoral muscles and subcutaneous tissues in separate layers, usually in a simple continuous pattern. Close the skin in routine fashion.

Exploratory thoracotomy

The principles for performing an exploratory thoracotomy are similar to those for performing an exploratory laparotomy: be thorough, consistent, and efficient. Exploration of the thoracic cavity focuses on two body systems: cardiovascular and respiratory. Craniocaudal visualization of the ventral aspect of the thoracic cavity is best accomplished through a median sternotomy, while dorsoventral visualization of a specific region of a hemithorax is enhanced by an intercostal thoracotomy.

Thoracostomy tube placement

A thoracostomy tube may be placed at the time of thoracotomy or as a separate procedure. Guidelines for tube selection suggest that cats will usually accept a 14 to 16 F tube. Dogs accept tubes ranging from 14 to 16 F (< 7 kg body weight), 18 to 22 F (7 to 15 kg body weight), 22 to 28 F (16 to 30 kg body weight), and 28 to 36 F (> 30 kg body weight).

Placement technique during a thoracotomy

Place a thoracostomy tube before closing the thoracotomy incision. Place the tube so that its skin exit point and thoracic wall entry point are offset. Cut additional holes in the thoracostomy tube near its end. Do not position the thoracostomy tube in the primary incision. Match the size of the tube to the patient size and its intended use (tube size in dogs with pleural effusions generally should be slightly larger than usually selected sizes). During a lateral thoracotomy, plan to have the tube enter the thoracic wall two intercostal spaces caudal to the primary thoracotomy incision. During a median sternotomy, tube placement is somewhat more challenging, as tunneling of the tube can be more difficult. Place the tube subcostally and lateral to the midline. Position the fenestrated end of the thoracostomy tube at the level of the second sternebrae and near the ventral aspect of the thoracic cavity. Connect the exterior of the thoracostomy tube to a three-way stopcock (requires an adaptor). Use suture to secure the tube to the skin using a friction suture pattern. Position a C-clamp on the tube below the three-way stopcock for added safety. Cover the thoracostomy tube with a bandage.

Placement technique as a separate procedure

Provide pleural drainage when sufficient air or fluid is present within the pleural space to cause respiratory distress. Perform thoracentesis initially for both diagnostic and therapeutic reasons. Use a thoracostomy tube when there is sufficient accumulation of air or fluid to warrant repeated pleural evacuation. A single thoracostomy tube is usually sufficient to control the pleural cavity in most dogs, although bilateral tubes may be used in dogs with pyothorax. Commercially available chest tubes are easier to insert because they contain a metal styletb. Risk of injury to underlying tissues may be increased when thoracostomy tubes are placed as a separate procedure compared to placing them in conjunction with a thoracotomy.

Create a small skin incision just larger than the tube diameter at the dorsal aspect of the caudal thorax (usually 9th to 11th intercostal space). Advance the tip of the tube subcutaneously about two intercostal spaces before inserting the tube into the pleural cavity. Use a controlled thrust to insert the end of the tube just through the chest wall. Remove the trocar, and advance the tube so that its end is level with the second intercostal space. Position the tube so that its tip is located in the ventral chest. Quickly insert an appropriately-sized adaptor and 3-way stopcock in the end of the tube. Place a friction suture to hold the tube in place securely. Evacuate the pleural cavity, and bandage the thoracostomy tube in place.

Conditions of the thoracic wall

The most frequently encountered thoracic wall conditions that have surgical implications are traumatic and neoplastic conditions.

Thoracic wall trauma

Rib fractures occur commonly in small animals, particularly after blunt trauma. Pain and hypoventilation may result. Most rib fractures are treated non-surgically with analgesics and bandage application. Penetrating thoracic wounds often result from dog fights. Assessing the extent of injury externally may result in underestimating the extent of damage, particularly to underlying tissues. The concept of hidden trauma is common in small animals with penetrating thoracic wounds. Many cases of penetrating thoracic wall trauma are treated non-surgically, in part, because of the potential for having severely traumatized deeper tissues which are unavailable for effective closure. An example of an injury that may require surgical intervention is flail chest. Flail chest occurs when several adjacent ribs have been fractured in at least two places and a segment of chest wall is unstable. The unstable (flail) segment moves paradoxically compared to the rest of the thoracic wall (i.e., in on inspiration and out on expiration). Stabilization of the unstable portion of chest wall may be necessary to improve ventilation. Place percutaneous sutures around the ribs and attach them to an external fixation device that spans the traumatized portion of chest wall. Use of a percutaneously-placed thoracostomy tube in patients with thoracic wall trauma can present additional challenges.

Thoracic wall neoplasia

Neoplasms of the thoracic wall may arise from pleura, ribs, musculature, or subcutaneous tissue. Soft tissue sarcomas (e.g., fibrosarcoma, hemangiopericytoma) involving the thoracic wall are encountered relatively frequently in veterinary patients. Primary tumors of the ribs or sternum are encountered less commonly. Differentiation of a thoracic wall tumor, especially one involving the pleura and an intra-thoracic tumor can be challenging. Most thoracic wall tumors present as a localized swelling of the thoracic wall, although pleural effusion may be seen occasionally. Weight loss and dyspnea may also be observed. Tumor staging is important in the preoperative planning process. Thoracic radiography is indicated to determine bone involvement, pleural effusion, and pulmonary metastasis. Computerized tomography is especially useful in planning surgical removal of soft tissue sarcomas. Cytologic or histologic evaluation of sample(s) from the mass (fine needle aspirates or incisional biopsy specimen) will help determine a definitive diagnosis prior to surgical excision.

Surgical resection with wide margins of grossly normal tissue is the treatment of choice. Full thickness resection of multiple ribs usually requires surgical reconstruction of the thoracic/abdominal wall by using synthetic material (polypropylene meshc). With tumors of the caudal thoracic wall, the diaphragm can be advanced cranial to the resection site. Such advancement may offer more options for closure of the surgical site. Because of the wide surgical excision usually performed, be sure to surgically prepare a generous area.

When excising the segment of thoracic/abdominal wall, the defect created is often rectangular in shape. Position an appropriately-sized (slight larger than the defect) and shaped piece of polypropylene mesh to cover the defect. Suture the mesh to the edges of the defect, taking care to draw the mesh tightly across the defect. If the mesh is positioned over the thorax, place a thoracostomy tube, and cover the mesh with either thoracic wall musculature or an omental pedicle flap. Close the subcutaneous tissue and skin in a routine fashion. Monitor the patient closely for local tumor recurrence.

Summary

Complications associated with thoracic surgery can be minimized by proper planning, selecting the appropriate approach, and correct use of a thoracostomy tube.

     • Finochietto rib retractor, Codman, Raynham, MA 02767

     • Trocar catheter, Deknatel, Inc., Fall River, MA 02720

     • Polypropylene mesh, C. R. Bard, Inc., Cranston, RI 02920

References & suggested reading

Orton EC. Thoracic wall. In Slatter D (ed). Textbook of Small Animal Surgery, 3rd ed. W. B. Saunders Co, Philadelphia, 2003, p 373.

Kolata RJ. Management of thoracic trauma. Vet Clin North Am Small Anim Pract 1981;11: 103.