Clinical Examination of Farm Animals - CYF MEDICAL DISTRIBUTION

Clinical Examination of the Respiratory System
Pasteurella isolates may be commensals. Longhandled
sterile swabs are used. Swabbing must be
vigorous to obtain samples of mucosal cells required
for virus isolation. Early clinical cases are preferable.
Material for virus analysis from the swabs must be
placed in viral transport medium.
Fibreoptic endoscopy
Endoscopy is covered in Chapter 5.
Radiography
Radiography is of limited value, especially in older
animals, and in many cases alternative investigative
procedures have proved more diagnostic.
In cattle the presence of the heart just anterior to
the elbow and the rumen caudal to the diaphragm
prevents reliable interpretation of the area of lung
overlying or adjacent to these structures. The interstitium
of the lungs is normally prominent and is not
a sign of interstitial pneumonia.
In the adult animal the increased thickness and
size of the thorax result in magnification of the normal
and abnormal making interpretation difficult
and unreliable. Heavy musculature of the shoulder
overlying the thorax restricts diagnostic imaging to
the caudal lobe. In addition, powerful radiographic
equipment is required and is usually only available
in referral centres.
Radiography in calves can be quite rewarding,
although to increase the examination of the anterior
lobes the forelimbs have to be pulled well forward.
Chemical restraint of compromised patients may
lead to an unacceptable risk.
Radiography has been used to assist the diagnosis
of reticular wires which have penetrated the thorax,
fractures of the ribs, lungworm, enzoootic calf
pneumonia, diffuse fibrosing alveolitis, pulmonary
abscessation, tuberculosis, emphysematous
bullae, pneumothorax, pleural effusions and pleural
adhesions.
Ultrasonography
This is a non-invasive technique that can provide useful
diagnostic information, although some experience is
required to interpret the images correctly.
The pleura and pulmonary surfaces of both
lung fields can be examined through the intercostal
spaces between the 7th and the 11th ribs. Sector transducers
are the most useful, but linear transducers
are more readily available. The highest resolution is
obtained with a high frequency transducer (usually
7.5 MHz) the and the greatest depth of penetration
obtained with a low frequency transducer (usually
3.5 MHz). To obtain diagnostic images the hair over
the lung field has to be clipped and contact gel
applied. Structural changes and changes in lung
density such as those found in pneumonia can be
detected. Free fluid, although rare in cattle, can be
detected. Focal abscesses can be identified.
Blood gas analysis and packed cell
volume (PCV)
Blood gas analysis needs to be performed rapidly and is
usually only available in referral centres. Hand-held cow
side machines are available but are expensive.
Blood gas analysis can be helpful in defining the
severity of an hypoxia or characterising acid/base
disorders. Arterial samples are the most useful, and
the auricular artery or coccygeal artery are usually
used.
The percentage oxygen saturation of arterial
heamaglobin can be measured using a pulse oximeter.
Oxyhaemaglobin and deoxyhaemaglobin differ
in their absorption of red and infrared light. Pulse
oximeters measure the absorption of red and infrared
light in non-pigmented skin. The degree of
light absorption is a function of the saturation of the
arterial haemaglobin. Pulse oximeters with protective
sheaths to block out extraneous light sources
have been used in calves. The sensors were attached
to shaved non-pigmented skin of the tail, the nonpigmented
areas of the scrotum or the vulva. Pulse
oximeters are portable, non-invasive, easy to use,
inexpensive and can be used with success in field
conditions.
Evidence of polycythaemia from an elevated PCV may
indicate chronic hypoxia.
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