Page 735 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

710 CHAPTER 3

VetBooks.ir PNEUMOTHORAX Clinical presentation
The clinical signs may range from a mild increase
Definition/overview
Pneumothorax is an accumulation of air or gas in the in respiratory rate and sweating to tachypnoea, dys-
pnoea and cyanosis. Oral mucous membrane colour
pleural space causing partial or total collapse of the is often abnormal but may range widely in appearance
lung. It is uncommon in horses and usually occurs as from pale to congested, toxic or cyanotic depending
a result of trauma. Pneumothorax is usually bilateral on the degree of pneumothorax and the underlying
due to the fenestrations in the mediastinum of horses. cause. On chest auscultation, lung sounds are absent
in the dorsal lung field and percussion may reveal
Aetiology/pathophysiology hyperresonance over the affected area. Subcutaneous
Pneumothorax may result from an open chest wound, emphysema, if present, may obscure these findings.
rib fracture, blunt trauma to the thorax, rupture of
an emphysematous vesicle on the surface of the lung, Differential diagnoses
barotrauma or spontaneously without evident cause. Diaphragmatic hernia and pleural effusion may pro-
Horses with pneumonia may develop bronchopleu- duce similar signs.
ral fistulas, resulting in pneumothorax. Procedures
of the thorax (e.g. surgery or lung biopsy) may also Diagnosis
result in pneumothorax. History, evidence of trauma to the thoracic cavity or
Air may enter the pleural cavity either through the presence of subcutaneous emphysema is sugges-
a wound in the thoracic wall, or by a defect in the tive. Thoracic radiographs are important. Air within
lung parenchyma allowing communication between the pleural space compresses the lung ventrally and
the airways and the pleural space. Simple pneu- is seen as an absence of pulmonary vasculature over
mothorax involves intrapleural pressure that is less the caudodorsal lung field, and a sharp lung border
than or equal to atmospheric pressure, such that air in the dorsal and caudal regions (Fig. 3.171).
may enter and exit the chest cavity freely with each Careful ultrasonographic examination of the
breath. In such cases, insufficient negative pressure middle and dorsal areas of the thorax may reveal air
is generated within the chest cavity to expand the artefact images. These air artefact images, in combi-
lungs for ventilation. In contrast, respiratory embar- nation with the inability to identify a sliding motion
rassment from tension pneumothorax escalates more between the visceral and parietal pleura, are findings
rapidly due to continued influx of air into the chest consistent with pneumothorax.
cavity while no exit of air is possible. In such cases the
intrapleural pressure quickly exceeds atmospheric Management
pressure and causes life-threatening compression of Treatment of the underlying disease or cause should
the lungs as the chest cavity fills with air. be addressed. Horses with simple pneumothorax

3.171

Fig. 3.171 Thoracic radiograph
of bilateral pneumothorax in an
adult horse. The arrows indicate
two distinct crura of the dorsal
lung lobes, displaced ventrally by
air within the plural space.