Principles of Thoracic Surgery

Chapter 167 Principles of Thoracic Surgery



Stephen J. Birchard, Eric R. Schertel


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.


Recently, minimally invasive thoracic exploratory (thoracoscopy) has become an alternative to traditional methods of thoracic surgery in veterinary medicine. Thoracoscopy requires specialized instrumentation and expertise, generally limiting its users to surgical specialists. Refer to the clinical literature and appropriate texts if more information on thoracoscopy is desired.


This chapter discusses surgical anatomy and physiology of the thorax, thoracic surgical technique, and patient care before, during, and after thoracic surgery.



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



• The external and internal intercostal muscles are located between each rib.

• 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.


Vessels and Nerves



• The intercostal arteries, veins, and nerves are located on the caudal aspect of each rib. The internal thoracic artery and veins run horizontally just lateral to the sternum, within the thorax.

• The cutaneous and muscular branches of the thoracodorsal artery are frequently encountered during lateral thoracotomy.


PREOPERATIVE CONSIDERATIONS



History, Physical Examination, and Diagnostic Tests



• Review the animal’s history and perform a thorough physical examination.

• 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).

• Review diagnostic tests already performed and repeat if necessary.

• 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.

• Evaluate blood tests, such as the complete blood count (CBC) and serum chemistry profile, to establish the patient’s baseline before surgery. If the condition is severe, blood gas analysis may be helpful to further evaluate the patient’s respiratory status.


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.

• Correct fluid and electrolyte deficiencies.

• Maintain the animal’s nutritional status. Consider placing a nasogastric, esophagostomy, or percutaneous endoscopic gastrostomy (PEG) tube if the animal will not eat and is becoming debilitated (see Chapter 3).


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).

• Use intermittent or continuous suction drainage.

• Quantify the amount of fluid or air recovered to establish a baseline before surgery.


Oxygen



• Administer oxygen to severely dyspneic or cyanotic animals.

• 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).

• If possible, analyze blood gases before and after oxygen administration to establish its effectiveness. Pulse oximetry may be useful as well.


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.

• Choose an antibiotic that is effective against the suspected contaminant and that reaches therapeutic concentrations in the target tissues.


Blood



• Cardiac surgery or removal of large, vascular neoplasms may be associated with significant blood loss.

• Ensure that a blood donor or packed cells are available if significant blood loss is anticipated.

• Cross-match or type the donor’s blood if multiple transfusions are anticipated.


Client Communication



Risks



• Major cardiac and respiratory surgery is associated with a high incidence of morbidity and mortality.

• Review the incidence of complications and death associated with the planned procedure and discuss this information with the client.


Cost


Thoracic surgery and patient care may be quite expensive. Discuss the cost of preoperative diagnosis and therapy, anesthesia and surgery, and postoperative intensive care with the client.



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.

• Avoid using anticholinergics (e.g., atropine) because they increase viscosity of respiratory secretions, can increase anatomic dead space, and may induce cardiac arrhythmias.


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.

• Propofol is another choice for induction of anesthesia. See Chapter 2 for indications and dosage.


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.

• Avoid nitrous oxide in patients with respiratory disease, pneumothorax, anemia, or hypoxia.

• 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.




Key Point


Adequate positive pressure ventilation in the thoracic surgery patient is essential for preventing hypoxia, respiratory acidosis, and atelectasis.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Principles of Thoracic Surgery

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