Page 736 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.4 Medical conditions of the lower respir atory tr act 711

VetBooks.ir can recover with confinement and rest. In case of to pleuropneumonia having a poorer prognosis com-
pared with other causes of pneumothorax.
hypoxaemia, intranasal oxygen insufflation can be
administered. Removal of the free air from the pleu-
ral cavity may be required in more severely affected CHYLOTHORAX
cases (Fig. 3.172). Air suction of the thoracic cav-
ity is performed in the upper mid-thorax between Definition/overview
the ribs; ultrasound will assist by revealing typical The accumulation of chyle in the pleural cavity is
air reverberations associated with the thorax, but infrequently reported in horses. Chylous fluid is
with no pleural movement. The area is surgically generally odourless and of milky and opalescent
prepared and the site desensitised with local anaes- appearance. Currently, the number of equine cases of
thetic. A full-thickness skin stab incision is made, chylothorax is limited to a few case reports in foals.
and a teat cannula or small-bore thoracic tube is
inserted into the pleural space. If suction equipment Aetiology/pathophysiology
is available, the cannula or tube is attached to the Conditions affecting the thoracic duct (e.g. congeni-
system and gentle suction is applied. Alternatively, tal abnormalities, traumatic rupture or neoplastic
a three-way stopcock tube system can be used, with erosion) are the most common causes of chylothorax
repeated aspiration of air using a large syringe. Once in humans and have been reported in domestic small
the air is removed from the chest cavity allowing animal species. However, in the majority of cases the
re-inflation of the lung, the cannula/tube should be cause is unknown. Similarly, in the majority of foals
removed, and the incision sutured closed. diagnosed with chylothorax, the cause could not be
determined.
Prognosis
The prognosis is commonly dictated by the under- Clinical presentation
lying cause, with cases of pneumothorax secondary Clinical signs reported in foals diagnosed with this
condition include tachypnoea, dyspnoea, cough,
lethargy and pyrexia. Muffled lung sounds on aus-
cultation have also been reported.
3.172
Differential diagnoses
Pleuropneumonia, haemothorax, hydrothorax and
diaphragmatic hernia should be considered.

Diagnosis
A fluid line is evident on chest percussion, with lung
sounds decreased in the ventral lung fields. Thoracic
ultrasonography is useful to detect fluid in the pleu-
ral cavity and to guide thoracocentesis. The physi-
cal appearance of the fluid is suggestive, but it is
important to distinguish between true chyle and
pseudochyle (Fig. 3.173). Chyle fluid does not clear
Fig. 3.172 Two indwelling chest drains were placed on centrifugation and chylomicron globules can be
in this horse to remove air (dorsal drain, red arrow) seen under microscopic examination. Special stain-
and pleural effusion (ventral drain, white arrow). ing with Sudan III or IV, or oil red 0, will confirm
Negative pressure was applied to the dorsal drain the chylomicron globules. Triglyceride levels are
using a suction apparatus. Heimlich valves were usually increased in chyle compared with serum.
attached to both drains for unidirectional movement Cytological analysis may be variable. Generally,
of gas and fluid, preventing further pneumothorax chyle is rich in lymphocytes, but in more chronic
developing from the presence of the drains. cases non- degenerate neutrophils may predominate.