Cats presenting with pleural effusion are nearly always in respiratory distress, ranging from an increased respiratory rate
and effort to open mouth breathing. In the latter situations, therapeutic intervention must be initiated quickly to prevent
respiratory arrest. The therapeutic intervention also provides your first diagnostic test. However, the other 2 rule-outs
for acute onset of severe respiratory distress is pulmonary edema secondary to cardiac failure and feline asthma. A rapid
decision must be made to determine which therapy is most appropriate for the underlying cause.
First, buy yourself some time, if possible, by placing the cat in an oxygen cage. Do not handle the cat until you have additional
historical information from the owner (coughing, possible cat bite, weight loss, etc.) and you can observe the cat for clues
as to the etiology. Radiographs are often not possible in a cat with severe respiratory distress so empiric therapy may be
the only option you have to avoid exacerbating the situation.
Nature of the dyspnea
Inspiratory vs. expiratory
With lower airway disease, the patient is breathing in and out through inflamed, narrowed, reactive airways; thus, the air
will need to be pushed out, producing a visible expiratory effort. This doesn't mean that the respiration rate is slow, simply
that the effort is increased and the expiratory phase is prolonged. At the other end of the spectrum are lungs that are either
compressed externally, i.e., by fluid or organs, or the airways are filled with fluids, e.g., heart failure. Pulling air
into the lungs is impaired – restrictive pattern – therefore inspiratory effort is increased.
With pleural effusion, breath sounds will be absent or muffled in the dependent lung fields. You may be able to auscultate
a distinct demarcation where the fluid begins. However, in long-standing effusive disorders, fibrosis causes pocketing of
fluids and the demarcation may not as distinct. Thoracocentesis in these patients is also challenging and often requires
the use of ultrasound.
• Inspiratory dyspnea
• Open-mouthed breathing/cyanosis/preference for sternal recumbency
On physical examination, you should begin to evaluate those systems that can contribute to pleural effusion, specifically
the cardiac system. Arrhythmia, murmurs and pulses should be assessed and the jugular veins observed for distention. Ascites
can suggest right-heart failure, for example, or be indicative of a hypoalbuminemic state. Fever should help you rank infectious
diseases high, but don't forget that neoplasia and immune-mediated diseases also result in fever. A fundic exam is a must
since FIP should be considered in cats with effusions of any kind. A thorough examination of the cat's body for evidence
of penetrating wounds is necessary.