Page 189 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 14
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Surgery of the lung

Nicholas J. Trout, David A. Puerto and Philipp D. Mayhew

Anatomy and physiology also result in decreased venous return and cardiac output
when the chest is a closed cavity. For these reasons
The lungs, which lie protected within the laterally com- thoracic surgery should only be undertaken by more
pressed thoracic skeleton, are divided into distinct lobes experienced practitioners.
by fissures, allowing them to accommodate the move-
ments of the thoracic wall and diaphragm. On the left side,
the lungs are divided into a cranial lobe, with a cranial and
caudal part, and a caudal lobe. The left pulmonary artery Diagnostic approach
lies cranial to the left bronchus; the left pulmonary vein lies
ventral to the left bronchus. The larger right lungs are The canine and feline respiratory patient must first be
divided into cranial, middle, caudal and accessory lobes. assessed by physical examination and stabilized prior to
any major diagnostics (see Chapters 1 and 2).
The right pulmonary artery is located dorsal and slightly
caudal to the right bronchus; the right pulmonary vein lies
ventral to the right bronchus. Imaging
Lung is absent from a small area between the heart
Thoracic radiography is indicated for most respiratory
and body wall at the ventral aspect of the fourth intercostal patients (for emergency situations, see Chapter 2). Radio-
space called the ‘cardiac notch’. A layer of mesothelial graphs may reveal airway disease (e.g. foreign body,
connective tissue covers both the lungs and the lining of
neoplasia, asthma, collapsing trachea), primary lung
the thorax, forming the visceral and parietal pleura, disease (e.g. pneumonia, lung lobe torsion, lung tumour),
respectively. These pleura come together at the caudal secondary lung disease (e.g. heart failure) or pleural space
lung lobes to make the pulmonary ligament; this ligament
disease (e.g. space-occupying mass, effusion, pneumo-
is severed to facilitate caudal lung lobectomy. thorax). The initial radiographic evaluation will determine
The lungs serve to exchange gases between inspired what additional diagnostics are appropriate for the patient.
air and pulmonary arterial blood, a process that occurs
Transthoracic ultrasonography can provide valuable
by simple diffusion at the level of capillaries and alveoli.
information about thoracic structures. It can be used to
In a resting state the process of inspiration is provided detect effusions and evaluate lung tissue where there is
mainly by diaphragmatic contraction, with expiration
consolidation or a mass lesion. Using ultrasound guid-
occurring passively from the elastic recoil of the lungs. In ance, accurate sampling of small pleural effusions and
more active states, inspiratory muscle groups are called lung lesions adjacent to the thoracic wall can be obtained
upon to pull the ribs cranially, thereby increasing intra- via fine-needle aspiration or needle biopsy. In one study,
thoracic volume, and expiratory muscle groups can be diagnostic samples were obtained in 51 of 56 patients
recruited to force expiration actively. The lungs are (Reichle and Wisner, 2000).
‘coupled’ to the thoracic wall by a small amount of pleural
fluid, such that changes in thoracic volume result in
WARNING
changes in lung volume.
Careful maintenance of alveolar ventilation is essential A 31% incidence of pneumothorax has been reported
during thoracic surgery. Thoracotomy disrupts the cou- following transthoracic needle biopsy of the lung
pling of the lungs to the thoracic wall, allowing the lungs (Teske et al., 1991)
to separate from the wall and collapse. During anaes-
thesia, manual or mechanical ventilation is essential to
maintain adequate oxygenation and ventilation, neces-
PRACTICAL TIP
sitating increased equipment and/or technical support to
undertake thoracic surgical procedures. Inappropriate Radiographs should be taken after lung aspiration or
rates of ventilation can result in gaseous and metabolic biopsy to determine whether pneumothorax has
abnormalities, and ventilation must be coordinated with occurred. In patients with unilateral air leakage, it may
the operating surgeon to prevent injury to the lungs during be beneficial to lay the patient in lateral recumbency
surgery. Inappropriate pressure of ventilation can result in with the affected side down (Zidulka, 1987)
barotrauma to the lungs. Positive-pressure ventilation can

180 BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, second edition. Edited by Daniel J. Brockman, David E. Holt and Gert ter Haar. ©BSAVA 2018

Ch14 HNT.indd 180 31/08/2018 13:20