Chapter 41


Cats with thoracic disease may present with a range of clinical signs, depending upon the organ system involved and the pathophysiology of the disease. Individual disease processes are covered in subsequent chapters.

Surgical intervention may be necessary for the management of a number of thoracic diseases in cats. Access to gas and fluid can be obtained by thoracocentesis or thoracostomy drain placement. Intercostal thoracotomy allows access to a limited area of one hemithorax and is well tolerated. Median sternotomy is more invasive but allows surgical access to the entire thoracic cavity.

Diagnostic approach to the cat with impaired respiratory function

A careful physical examination is imperative for animals presenting with clinical signs attributable to thoracic disease. Hyperpnea and tachypnea (Table 41-1) are common physical examination findings.

Cats may often compensate for impaired respiratory function by becoming less active and owners may not notice clinical signs until they are severe. Cats are therefore more likely to be severely affected at first presentation than dogs with the same disease. Observation of the cat prior to physical examination should recognize those cats that are at risk of respiratory embarrassment during physical examination. When necessary, measures to prevent a respiratory crisis (such as providing oxygen support, but also interventions such as thoracocentesis) should never be delayed but should be undertaken in such a way as to minimize handling or restraint. Indicators of impending respiratory crisis are listed in Box 41-1.

Careful observation of the pattern of respiration may help determine the type of thoracic disease present (Table 41-2). For example, pleural disease may result in short shallow respiration, whereas upper respiratory obstruction is more likely to result in a long deep inspiratory pattern. Thoracic auscultation also provides highly valuable additional information. Firstly, a basic assessment of whether or not there are audible breath sounds needs to be made and if breath sounds are absent, locating where the sounds are missing can rapidly help in identifying the type of pathology present. The use of gentle percussion must also always accompany auscultation to help identify fluid lines in cases of, for example, pyothorax. If breath sounds are auscultatable, then assessing whether they are appropriate for the respiratory effort of the patient is the next step. In a normal cat, breath sounds are quiet but audible, and they naturally become louder as respiratory rate increases e.g., with stress, exertion. However, increased respiratory rate does not normally generate abnormal breath sounds, so the identification of crackles or wheezes indicates the presence of pulmonary pathology and should always be investigated. It is also important to distinguish abnormal lower respiratory tract sounds from referred upper airway noise caused by upper respiratory tract disease.

Prior to any diagnostic or therapeutic intervention, and certainly prior to anesthesia, pre-oxygenation is recommended to improve oxygen delivery to tissues in patients with compromised respiratory function (Fig. 41-1). Whilst an oxygen cage or incubator provides the greatest fractional inspired concentration of oxygen, they are rarely available and do not allow concurrent physical examination. The practitioner may have to rely on mask or flow-by techniques, which only provide a minimal increase in fractional inspired oxygen compared to room air. Cats may find restraint, supplemental oxygenation, and diagnostic techniques distressing, leading to an increase in oxygen consumption and risk of further respiratory distress. Careful, continual assessment is therefore vital to ensure that attempted stabilization methods do not worsen the clinical status of the patient.

The choice of diagnostic test is determined by history and physical examination findings. If a pleural effusion is suspected, thoracocentesis should be performed, preferably after a brief ultrasound scan to confirm the presence of pleural fluid (Box 41-2, Fig. 41-2). Thoracocentesis can be both diagnostic and therapeutic and is often safer to perform than radiography, which may require manual or chemical restraint.

Box 41-2   Thoracocentesis

In most cats, thoracocentesis can be performed with the cat sitting or in sternal recumbency with minimal restraint. Following clipping and aseptic preparation of the lateral thoracic wall, a 19–22G butterfly needle attached to a syringe via a three-way tap is introduced at a 45° angle in the seventh or eighth intercostal space. The needle should be positioned immediately adjacent to the cranial aspect of the rib to avoid the intercostal neurovascular bundle on the caudal aspect of the rib. If a butterfly needle is not available then an intravenous catheter or a hypodermic needle can be used. If the presence of air is suspected the needle can be inserted in the dorsal third of the thoracic cavity; if fluid is suspected the needle can be inserted in the ventral third, but care must be taken to avoid the internal thoracic artery which lies ventral and deep to the costochondral junctions. If the nature of pleural disease is unknown the needle is generally placed halfway down the thoracic cavity. It is preferable to have three people present; one to monitor the cat and administer oxygen, a second to drain the chest via an extension tube, whilst the third holds the needle to assess the point at which the lungs are felt on the needle tip, thereby signaling the time to stop drainage. In practice it is possible for one person to drain the chest with just a single assistant, especially in cats, where the needle is less likely to be displaced from the thorax during respiratory excursions than in dogs. The absence of a complete mediastinum in most cats means that drainage of air or fluid from both hemithoraces can usually be achieved with unilateral thoracocentesis. However, trial thoracocentesis on the contralateral side is warranted if clinical signs do not improve significantly following unilateral drainage, particularly in cases where loculation of fluid may be present (e.g., pyothorax). Any pleural fluid should be placed into an EDTA tube in addition to direct smears being made for cytology, and into a plain tube for bacteriologic culture and sensitivity testing (Fig. 41-3).

Diagnostic imaging for thoracic disease

Thoracic radiography can provide extremely useful information on the causal pathology of thoracic diseases (see Chapter 8), and should be undertaken following evacuation of pleural fluid or air and with minimal stress. In many circumstances a single dorsoventral radiograph may be sufficient to make a preliminary diagnosis, and it can be followed by a complete imaging study under sedation or anesthesia when the cat is more stable (Fig. 41-4). Thoracic radiography will indicate the presence or absence of pathology within the thoracic wall, lungs, and mediastinum, but it may be difficult to differentiate soft tissue structures and determine the exact location of disease. Ultrasonography is extremely useful for imaging patients that have pleural effusions, mediastinal disease, and lung lobe consolidation and in patients with mass lesions. Both ultrasound and computed tomography (CT) can be used to obtain fine needle aspirates and needle core biopsies, which can be submitted for cytology, histopathology, and bacteriologic/fungal culture and sensitivity (Fig. 41-5). The three-dimensional imaging techniques, especially CT, have made a significant impact on managing feline thoracic disease (Figs 41-6 and 41-7). CT is more sensitive in detecting metastatic pulmonary disease than radiography and localization of thoracic disease makes surgical planning and choice of thoracotomy approach easier. Due to the more accurate lesion localization afforded, more animals are likely to undergo lateral thoracotomy than median sternotomy if CT is available.

Preparation for thoracic surgery

Before surgery is ever undertaken, it is vital to recognize the cases in which appropriate medical management of the disease before surgery is likely to improve clinical parameters (e.g., allowing time for pulmonary contusions to improve following trauma) and in such cases this should always be performed. Likewise, the attending clinician should also recognize cases in which rapid surgical intervention is required as soon as the cat is cardiovascularly stable or as stable as can be achieved (e.g., clinically significant intrathoracic hemorrhage following trauma).

Depending upon the disease process for which thoracotomy is being performed, cats may have an American Society of Anesthesiologists (ASA) score varying from ASA 2–3 (a patient with mild to severe systemic disease, e.g., patent ductus arteriosus) to ASA 5 (a moribund patient in whom surgery is performed in desperation due to the life-threatening nature of their disease). Extreme care must be taken to try to prevent deterioration of clinical parameters during induction and maintenance of anesthesia. As previously described, a period of pre-oxygenation (e.g., five minutes) can be beneficial in most cases.

The correct choice of which premedicant and induction agent to use is vital, to allow the induction of anesthesia with minimum stress, whilst avoiding excessive respiratory or cardiac depression.1 Intravenous induction, establishing a patent airway, and being able to ventilate if necessary, are all instrumental to safe induction of anesthesia. Intraoperative monitoring is also extremely important and should include serial monitoring of heart and respiratory rate, pulse oximetry, capnography, ECG, and core body temperature. Mechanical ventilation is required during thoracotomy, and also in laparotomies where the diaphragm is not intact, as opening the pleural space very significantly restricts effective natural ventilation. Mechanical ventilation may also be required prior to surgery when the underlying disease prevents effective chest excursions. Mechanical ventilators are easily applied to cats (Fig. 41-8), but careful manual ventilation is also acceptable. Care must be taken not to apply too much pressure during ventilation as this can cause lung damage.

Thoracotomy can lead to significant fluid and heat loss, and this can be especially relevant in cats due to their small body size, hence the need for regular monitoring of the patient’s core body temperature. Warming methods, such as the use of warm fluids, bubble wrap application to extremities, warm air heating systems (e.g., Bair Hugger, 3M), low fresh gas flows, and heat/moisture exchangers (e.g., Thermovent) should all be considered and utilized whenever necessary. Keeping anesthetic and surgical times to a minimum can be very helpful in this regard and excessive wetting of the skin and hair is avoided during preoperative preparation and thoracic lavage.

One of the major limiting factors to successful surgery is small patient size, but it is aided by the use of fine instruments. Additional instruments that will be helpful for thoracic surgery are listed in Box 41-3 (and see Chapter 13). These include vascular clamps for the control of hemorrhage from large vessels, such as the pulmonary artery, as well as diathermy for hemorrhage from smaller vessels.

Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Thoracotomy
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