CPD Article | EQUINE
Pleural effusion is present if there is more than 3.5cm
fluid identified in the ventral part of the thorax 15 . Lung
ultrasound evaluation is limited to superficial lesions
or peripheral lung fields and the pleural space 3 as
parenchymal lesions overlying aerated lung tissue will
not be detected 3 15 .
With the presence of pleural effusion confirmed,
thoracocentesis 5 should be ideally performed as the
next diagnostic procedure to obtain a pleural fluid
sample prior to administration of anti-microbials 9 ,
although this may not always be practical. The
caudal mediastinum is fenestrated, however this
fenestration may be blocked with fibrin deposition 3
or cellular debri 2 therefore a sample from each
hemithorax should be obtained in cases where
bilateral effusion is identified 2 11 . Thoracentesis may be
both diagnostic and therapeutic as once a chest drain
is placed, large volumes of effusion can be drained,
thus reducing respiratory distress 11 and allowing for
lung re expansion 3 . Samples must be submitted for
aerobic and anaerobic culture and sensitivity 6 . A
drop of the pleural effusion can be smeared, air dried
and gram stained 9 for immediate evaluation. The
resultant cytological staining may give an indication
of causative organisms 9 and help guide appropriate
antimicrobial therapy pending culture results9. Gas
detected in the pleural effusion on thoracic ultrasound
imaging may indicate that anaerobic bacteria are
present 9 .
Pleural Fluid Analysis:
Normal pleural fluid 3 1
Nucleated cell count: ≤8 000 cells/ul
TSP ≤2.5g/dl
Clear – light yellow fluid
No smell
Abnormal pleural fluid 3
Nucleated cell count: ≤10 000 cells/ul (+90%
neutrophils)
TSP ≥2.5g/dl
Cloudiness or colour change evident
Foetid odour
Thoracocentesis is performed at the level of the
costochondral junction in the 7th and 8th intercostal
space 11 . For sample collection or small volume
drainage, a blunt teat cannula can be used 3 . A
24 -32 Fr chest tube with a 1 way valve (e.g. a
condom witht he tip cut open or Heimlich valve)
can be inserted and left as an in dwelling drain for
continuous fluid drainage 3 . The type of drainage used
– single, intermittent or continuous is determined
by the volume and character of the pleural effusio 13 .
With severe effusions, between 30 -50 L can be
drained from the pleural space 11 . Thoracocentesis or
chest drain placement should be performed under
ultrasound guidance 3 to ensure accurate placement.
Possible complications arising from thoracocentesi s11
are: pneumothorax, lung laceration, haemothorax,
cardiac arrhythmias, organ puncture (heart / liver) and
a localized cellulitis 3 .
A TTA sample often yields the causative organism and
therefore should always be performed 3 7 especially if
there is not a large pleural effusion volume evident. It
also allows other potential causes of pleural effusion
to be excluded 10 .
Chest radiographs 13 can be performed after drainage
of the pleural effusion to evaluate the extent of the
pneumonia 10 , assess the mediastinal structures 13 ,
detect the presence and severity of a pneumothorax 13
and examine possible deep leions 11 .
• Volume 20 Issue 3 | October 2018 •
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