Page 174 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 12 · Pleural drainage techniques

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(a)

(b) (c) (d)
Lateral (a) radiograph and (b) sagittal computed tomographic image and (c) dorsoventral radiograph of a cat with a penetrating foreign body
12.8
in the distal oesophagus removed via a right 10th intercostal thoracotomy. (d) The preoperative imaging was critical in determining the tract
of the foreign body and therefore whether a lateral thoracotomy approach would be preferable to a median sternotomy.

Postoperative care: Animals with pyothorax require inten- fats that have been digested and absorbed. Once formed,
sive care and monitoring, especially for the first 24–48 hours the chylomicrons are secreted into intestinal lymphatics
after surgery. Septic shock and systemic inflammatory that drain into the cisterna chyli and thence into the
response syndrome may develop. Fluid therapy in the post- TDS. Thoracic duct lymph also contains fluid and proteins
operative phase is very important and often consists of similar in type and concentration to those of plasma. A
crystalloids, colloids and blood products. Vasopressors large amount of fluid and protein leaks out of normal capil-
may be needed to treat refractory hypotension once volume lary beds continuously, and the TDS provides a major
expansion has been accomplished. Respiratory, acid–base pathway for the return of fluid and protein from the inter-
and electrolyte abnormalities should be evaluated and stitial space to the circulation. The proteins, including albu-
treated as needed. These patients are at high risk for the min and various globulins, are important in maintaining
development of disseminated intravascular coagulation and normal colloidal osmotic pressure and immune function,
need to have their coagulation parameters monitored and in the transport of protein-bound hormones and
closely. Daily evaluation of the complete blood count and drugs. Thoracic duct lymph also contains electrolytes
cytology of the pleural effusion are necessary. and trace minerals. The main cellular component of lymph
is the small lymphocyte.
Prognosis
Thoracic duct system
A poor prognosis and frequent recurrence have been
reported in both cats and dogs. Many patients may be In both dogs and cats the anatomy of the ‘thoracic duct’ is
euthanased on the basis of these reports and because of quite variable, both in location and in the number of ducts
present. The thoracic duct is probably more appropriately
owners’ financial constraints, thereby perpetuating the
referred to as the ‘thoracic duct system’ (TDS).
poor prognosis. In cats and dogs that receive aggressive
medical and surgical therapy, as deemed appropriate, sur- Dogs: In dogs the TDS generally begins its course on the
vival is >50%, with a recurrence rate of <10%. Many of
right side of the mediastinum dorsal to the aorta. In a
the patients with pyothorax that do not survive either die
study of 20 dogs, only one dog had a single vessel in the
naturally or are euthanased within the first 24 hours of
caudal mediastinum; five had two collateral vessels and
presentation; the survival rate increases significantly for 14 had three or more vessels (Kagen and Breznock, 1979).
patients that are alive 24 hours after admission (Rooney Most of the collateral vessels were in close relation.
and Monnet, 2002; Waddell et al., 2002). However, in some dogs, portions of the vessel system
crossed the midline in widely distinct areas (over three
Chylothorax vertebral spaces), creating a situation where there were
lymphatic vessels on both the left and the right sides of
Chylothorax is an accumulation of lymphatic fluid leaking the caudal mediastinum at the same time. In many dogs,
from the TDS into the pleural space. Thoracic duct fluid the TDS crosses the midline from right to left between
has three main sources: lymph from the intestines; lymph the levels of the fifth and 11th thoracic vertebrae. In
of hepatic origin; and lymph from the hindquarters. The others, the TDS remains right-sided and enters veins or
term ‘chyle’ refers to lymphatic fluid drained from lymph nodes in the right hemithorax. Many normal dogs
the intestines. It is the high fat content of intestinal lymph develop a single lymphatic vessel in the cranial media-
that gives chylous fluid its milky appearance. This fat is stinum that ends at the junction of the jugular and brachio -
mainly in the form of chylomicrons, which are aggregates cephalic veins with the cranial vena cava. Other dogs
of triglycerides, phospholipids, lipoproteins and choles- have multiple lymphatic vessels, which send some
terol, formed in the intestinal epithelial cells from dietary ter minal branches to mediastinal lymph nodes.

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