Chapter 167 Principles of Thoracic Surgery
Thoracic surgery frequently is performed in small animals for a variety of disorders, especially in referral centers. Thoracotomy is commonly performed to correct routine cardiovascular defects such as patent ductus arteriosus and to evaluate and correct respiratory diseases such as pulmonary neoplasia. Exploratory thoracotomy may be indicated to determine the extent of diseases such as neoplasia and diffuse infection and to obtain biopsies to help establish a definitive diagnosis. It is important to be well versed in the anatomy and physiology of the thoracic cavity and its major structures and to be familiar with the principles of anesthetic management of the thoracic surgery patient.
SURGICAL ANATOMY
Bony Structures
• The bony structures of the thorax usually consist of 13 pairs of ribs and costal cartilages, 13 vertebrae, and 8 sternebrae.
• The first 9 ribs, called the sternal ribs, articulate with the sternum. The last 4 ribs are called the asternal ribs. The costal cartilages of ribs 10 to 12 make up the costal arch. The 13th pair of ribs is also called the floating ribs.
• The manubrium is the most cranial aspect of the sternum, and the xiphoid is located caudally. The xiphoid cartilage is the caudal extension of the xiphoid. Intersternebral cartilages are located between each sternebra. The sternebrae are very narrow structures, making midline division somewhat difficult. The sternebral midline is characterized by a slight bony ridge.
Soft Tissues
Muscles
• Other surgically important muscles of the lateral thoracic wall are the serratus ventralis and serratus cranialis dorsalis, the scalenus, and the external abdominal oblique. The latissimus dorsi, a large, fan-shaped muscle extending from the ribs to the forelimb, is the first major muscle encountered during lateral thoracotomy.
PREOPERATIVE CONSIDERATIONS
History, Physical Examination, and Diagnostic Tests
• Give special consideration to the patient’s cardiopulmonary status (mucous membrane color and refill time, heart rate and rhythm, pulse rate and character, heart and lung sounds, ventilation, thoracic palpation and percussion).
• Evaluate thoracic radiographs and other diagnostic images to become familiar with the animal’s disease and to plan the surgical approach. Thoracic ultrasound may assist in planning the surgical approach. Advanced imaging (computed tomography, magnetic resonance imaging) may be of benefit in selected cases.
Preoperative Treatment and Stabilization
General Supportive Care
• Closely observe the patient’s condition. The clinical states of animals with thoracic disease may change rapidly.
• Administer appropriate medical therapy that will stabilize the animal and reduce the level of anesthetic and surgical risk.
• For example, if a dog with patent ductus arteriosus is in congestive heart failure, treat with the appropriate drugs to improve cardiopulmonary function before anesthesia and surgery.
Thoracic Drainage
• If pleural fluid or air is present, perform thoracentesis before anesthesia to allow better ventilation (see Chapter 3).
• Place an indwelling thoracic drainage tube if fluid or air accumulation is recurrent (see Chapter 3).
Oxygen
• Place the animal in an oxygen cage with a 40% to 50% concentration or place a nasal oxygen tube to raise the concentration of inspired oxygen (see Chapter 3).
Prophylactic Antibiotics
• Use prophylactic antibiotics if the planned operation will be a clean-contaminated, contaminated, or “dirty” procedure.
• Thoracotomy to open and/or resect a portion of the respiratory tract is considered a clean-contaminated procedure. However, we use prophylactic antibiotics only if there is a strong suspicion that contamination of the surgical field will occur (e.g., foreign bodies, abscess, necrotic tumor, or bacterial pneumonia). Thoracotomy for drainage and resection of the pericardium for pericarditis is an example of an indication for preoperative use of antibiotics.
• Administer the prophylactic antibiotic immediately before surgery to ensure sufficient blood concentrations of the drug at the time of surgery. Discon-tinue antibiotic administration 24 to 48 hours postoperatively unless evidence of infection is present.
ANESTHETIC CONSIDERATIONS
The general principles of anesthesia described in Chapter 2 apply to thoracic surgery patients. Special considerations for thoracic surgery patients are outlined in this section.
Premedication
• Consider placing a transdermal fentanyl patch on the animal 12 hours prior to surgery for analgesia (see Chapter 6).
• Generally avoid phenothiazines such as acepromazine because of possible side effects of hypotension and myocardial depression. However, at low doses (up to 0.1 mg/kg SC or IM), they may be beneficial for calming animals with respiratory compromise but normal cardiac function. Acepromazine can be combined with one of the opiates (e.g., butorphanol) as an effective preanesthetic treatment (see Chapter 2).
• Diazepam (Valium) is a safe drug that can be used as a premedicant (0.2 mg/kg IV). It has minimal effects on the cardiovascular and respiratory systems.
• Xylazine (Rompun, Miles) causes undesirable cardiac and respiratory depression, making it a poor choice for thoracic surgery.
Induction
• Diazepam, 0.2 mg/kg IV, followed by administration of a thiobarbiturate (e.g., thiopental), 6 to 10 mg/kg IV, provides relatively safe and rapid, smooth induction that allows immediate intubation and control of ventilation.
• The combination of ketamine and diazepam (1:1 mixture; 1 ml of mixture per 10 kg) also can be used for thoracic surgery patients. Hemodynamics is minimally compromised by this combination. However, ventilatory support may be necessary.
Maintenance
• Any of the commonly used inhalation anesthetics can be used successfully for thoracic procedures. Isoflurane is preferred because of less myocardial depression, although hypotension commonly occurs.
• Provide positive pressure ventilation by manual compression of the bag or with a mechanical ventilator (see Table 167-1 for ventilation guidelines).
Table 167-1 GENERAL GUIDELINES FOR CONTROLLED VENTILATION
| Physiologic Parameter | Value |
|---|---|
| Respiratory | 8–12 breaths/min |
| Tidal volume | 15–20 ml/kg of ideal body weight |
| Peak airway pressure | 15–20 cm H2O—closed |
| 20–30 cm H2O—open | |
| Inspiratory time | 1–1.5 sec |
| Expiratory time | 2–3 sec |
| Inspiratory-to-expiratory ratio | 1:2–1:4 |
Modified from Faggella AM, Raffe MR: Anesthetic management of thoracotomy. Vet Clin North Am 17:480, 1987.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
