Introduction

Diseases of the thorax are frequently encountered in small animal practice and many require surgical intervention for definitive diagnosis and treatment. Two approaches to the thoracic cavity are the 1) intercostal thoracotomy and 2) median sternotomy, with each approach having advantages and disadvantages. Minimally invasive approaches to the thoracic cavity have also been described in small animal and will be covered briefly in lecture. In order to perform thoracic surgery the practitioner should have a strong familiarity with thoracic anatomy and the availability of instrumentation/equipment. In addition, the practice must have the ability to provide 24 h patient monitoring and the ability to provide multi-modal analgesia as approaches to the thorax are painful as a result of intramuscular and/or sternotomy incisions.

Indications

There are many indications for the performing surgery of the thorax. The practitioner should select their cases carefully to optimize outcome. Indications include lung lobectomy for neoplasia, torsion, abscess, trauma, spontaneous pneumothorax (bulla/bleb), thoracic trauma, pericardial disease, pleural space disease (chylothorax, pyothorax, hemothorax), and congenital heart disease (persistent right aortic arch, patent ductus arteriosus).

Approaches

Intercostal Thoracotomy

The intercostal space (ICS) for surgery will depend upon target structure/site. A table providing optimal ICS dependent on target site is provided below. An incision is created through the skin, subcutaneous tissues and cutaneous trunci. An incision just caudal to the level of the caudal scapula will be approximately at the 4th ICS. Digital palpation of ribs can be performed prior to incision to provide a good approximation of location of initial skin incision. The incision is made parallel to the ribs extending from ventral to the costovertebral junction to proximal to the sternum. The latissimus dorsi muscle is encountered and incised along the same direction as the original incision. The author performs partial incision of the most ventral aspect of this muscle and then places a stay suture to provide retraction in an attempt to limit morbidity associated with myotomy of the latissimus dorsi.

Ventral to the latissimus dorsi is the pectoralis muscle and this may need to be incised as well. The serratus ventralis muscle will then be visible with its finger-like muscle bellies just dorsal to the strap shaped scalenus muscle which is identified by its insertion on the 5th rib. The scalenus muscle is incised through its tendon and the serratus ventralis muscle bellies separated to expose the external intercostal muscles that are between ribs. The external and then internal intercostal muscles are carefully incised midway between the ribs to prevent trauma to the neurovascular bundle located on the caudal aspect of the ribs to expose the parietal pleura which is bluntly penetrated allowing pneumothorax which will allow the organs to fall away from the thoracotomy incision. The pleural incision should be extended ventrally to the level of the internal thoracic artery that can be palpated digitally. The remainder of the pleura is incised and rib retractors placed to provide exposure to the thoracic cavity.

Prior to closure, a thoracic drainage catheter or thoracostomy tube is inserted and sutured in place. Closure of an intercostal thoracotomy is performed by first placing circumcostal sutures around the rib cranial and caudal to the thoracotomy incision using a long acting, monofilament suture. These are placed as stay sutures initially to allow for visual guidance during placement preventing iatrogenic trauma to the thoracic organs. Once they have all been placed the ribs are approximated and the preplaced sutures tied. The serratus ventralis and scalenus muscles are closed followed by the latissimus dorsi muscle in layers. The subcutaneous tissues and cutaneous trunci muscles are then closed routinely followed by the skin.

Modified from, Textbook of Small Animal Surgery, S. Johnston and K. Tobias.

Median Sternotomy

Median sternotomy is the approach to the thorax used when the entire thoracic cavity needs to be explored. Common indications for performing sternotomy include pyothorax, mediastinal masses, spontaneous pneumothorax and thoracic trauma. Many surgeons believe this approach is associated with a high complication rate, however, with appropriate technique and perioperative multi-modal analgesia, sternotomy can be associated with very good outcomes. This approach does not provide good access to dorsally based structures such as the pulmonary hilus and thoracic duct, and total lung lobectomy is more easily performed from an intercostal thoracotomy approach.

With the animal in dorsal recumbency the entire ventro-lateral aspect of the thorax is prepared for surgery. The skin and subcutaneous tissues overlying the sternum are incised. The pectoralis muscle is encountered next and is elevated from the sternebrae using a combination of electrocautery and sharp dissection. An oscillating bone saw is used to perform a sternotomy. Generally, this author tries to leave the manubrium and the xiphoid process intact to maintain stability of the sternum postoperatively. A rib spreader is placed in the sternotomy to improve thoracic exposure. The author has combined the sternotomy with a ventral midline laparotomy in cases where a bicavitary approach is required. Prior to closure, a thoracic drainage catheter or thoracostomy tube is inserted into the thoracic cavity and sutured in place.

For sternotomy closure, orthopedic wire is placed in a figure-of-eight pattern around each sternebrae incorporating a costosternal junction for maximum stability. The pectoralis muscle, subcutaneous tissues and skin are closed routinely.

Perioperative Analgesia

Thoracotomy, regardless of approach, is a painful procedure and multimodal analgesia in the perioperative period is essential. Prior to intercostal thoracotomy surgery local anesthetics (bupivacaine/lidocaine) can be instilled over the intercostal nerves cranial and caudal to the site. High epidural analgesia can be provided with morphine and bupivacaine. Opioid analgesia is administered using constant rate infusions. Nonsteroidal anti-inflammatory therapy is administered if contraindications are not present. Intracavitary bupivacaine can also be administered post-operatively, however, at this authors institution this procedure is not commonly used and instead a wound soaker catheter placed in the surgical site (intercostal thoracotomy/median sternotomy) is used to administer local anesthetic in the postoperative period.

Conclusion

Thoracotomy is commonly performed for a variety of thoracic surgical diseases in companion animals. With appropriate knowledge of thoracic anatomy, equipment and multi-modal analgesia, thoracotomy can result in good outcomes for the treatment of thoracic diseases.