Page 168 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 12 · Pleural drainage techniques

Continuous monitoring of the animal is mandatory Clinical signs
when using a continuous drainage system because un - The respiratory signs caused by pleural disease are all
VetBooks.ir a life-threatening pneumothorax. secondary to reduced lung expansion (and tidal volume),
noticed disconnection of the system could rapidly lead to
which initially results in rapid shallow breathing. The dysp-
noea may also be characterized by prolonged inspiration
Drain removal
exhibit a ‘sprung’ or distended chest and position itself
Chest drains may be removed when there is no air leakage and increased abdominal effort. Ultimately, the animal may
and the amount of fluid being produced has reduced to a with the elbows abducted and neck extended to minimize
consistently small volume (ideally <2 ml fluid/kg/day). In any resistance to breathing. If hypoxia becomes severe the
practice the amount of fluid produced is highly variable mucous membranes can become cyanotic.
and the presence of a chest drain provokes an inflamma- Thoracic auscultation reveals diminished lung and heart
tory response, which means that fluid in the pleural space sounds. With pleural effusion, lung sounds are absent
rarely resolves completely until the chest drain is removed. ventrally but often still present dorsally. Percussion of the
thorax produces a dull hyporesonant sound in the presence
In animals that have undergone a simple thoracotomy
procedure, this may mean that the chest drain is removed of pleural fluid and a hyper-resonant ‘ping’ if pleural air is
present. In a series of 81 dogs with pleural and mediastinal
within hours of placement, but in other situations chest
drains may remain in place for several days. effusions, tachypnoea and/or dyspnoea was present in 91%
and muffled heart sounds in 41% (Mellanby et al., 2002).
The degree of respiratory compromise is generally
Complications proportional to the volume of fluid or air within the pleural
Common complications associated with chest drains cavity and the rate of accumulation. Fluid that accumulates
include: gradually may reach a large volume and produce only subtle
clin cal signs. Once a certain volume is exceeded, critical
i
• Leaks around the tube due to a wide subcutaneous respiratory compromise exists and rapid decompensation
tunnel can occur if the patient is not handled extremely cautiously.
• Leaks at improperly secured connectors In a series of 82 cats with pleural effusion, most were
• Backing out of the tube due to a poorly placed Chinese presented with acute disease but the duration of clinical
fingertrap suture. signs ranged from <12 hours to >12 months (mean 11.2
days) (Davies and Forrester, 1996).
Inadequate drainage can also be a problem and may Depending on the underlying cause, additional findings
require slight repositioning of the tube (commonly the tip in patients with pleural disease may include coughing,
of the tube is too far cranial in the chest and is obstructed pyrexia, depression, anorexia, weight loss, arrhythmias,
by mediastinal tissues), or the tube may be blocked and murmurs, ascites, lymphadenopathy, pale mucous mem-
require flushing. The longer a chest drain is in place, the branes and chorioretinitis.
greater is the risk of ascending nosocomial infection
(pyothorax); everything possible must be done to keep Pneumothorax
the bandage, tube connections and the animal’s environ- Pneumothorax may develop following rupture of the
ment clean. Lung injury is possible if excessive negative oesophagus, chest wall, lung, bronchi or trachea. As air
pressure is exerted via the chest drain (using either a
enters the pleural space it prevents normal lung expansion
syringe or a suction device). No more than 5–10 ml of during inspiration. If the site of air leakage acts as a one-
vacuum in a syringe is recommended when draining the
way valve, a tension pneumothorax develops, creating
thorax. Re-expansion pulmonary oedema may occur in supraphysiological pleural pressures that dramatically
chronic disease conditions when the lungs are adapted compress the lungs and great veins. Causes of pneumo-
to a contracted state and are unable to cope with rapid
thorax may be grouped into those of traumatic origin and
and complete evacuation of the pleural cavity. If re- those arising spontaneously; the aetiology and manage-
expansion oedema is considered a possibility, the chest
ment of these conditions is discussed in Chapter 14.
should be drained in small incremental stages over at
least 24 hours. Occasionally, the presence of the chest Diagnostic imaging
drain can cause phrenic nerve irritation, Horner’s syn-
drome or cardiac arrhythmias. The radiographic appearance of pneumothorax is charac-
terized by retraction of the lungs away from the thoracic
wall, resulting in a radiolucent space between the lung and
thoracic wall that does not contain lung markings. The
Pleural disease lungs have increased opacity because they are com-
pressed by pleural air. Separation of the heart from the
Pathological or traumatic conditions affecting the pleural sternum is commonly seen on a lateral radiograph and is
space produce respiratory compromise through the due to lack of underlying inflated lungs, which results in
accumulation of air (pneumothorax), fluid (pleural effu- displacement of the heart from its normal ventral position
sion) or both. Soft tissue can also occupy the pleural into the dependent hemithorax (Figure 12.2).
space, such as abdominal organs protruding through a With tension pneumothorax, the increased pleural pres-
diaphragmatic rupture. Although unilateral pleural effu- sure results in progressive caudal displacement of the
sion or pneumothorax is occasionally seen, both are diaphragm, and the lungs may become dramatically com-
commonly bilateral in dogs and cats, suggesting that the pressed against the midline. On a lateral radiograph the
mediastinum is easily disrupted or functionally incom- diaphragm appears ‘flattened’; on DV views the costal
plete. By extension, it is often assumed that drainage of attachments of the diaphragm may become visible. In uni-
one hemithorax also provides drainage of the other side, lateral tension pneumothorax the media stinum is shifted
but this is not always the case. towards the unaffected side (Figure 12.3).

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