Page 120 - Problem-Based Feline Medicine

112 PART 2 CAT WITH LOWER RESPIRATORY TRACT OR CARDIAC SIGNS

INTRODUCTION CARDIAC HYPOXIA

MECHANISM? CARDIOMYOPATHY***
Cyanosis is bluish discoloration of the skin and/or
Classical signs
mucous membranes due to reduced oxygen saturation
of hemoglobin in the blood causing hypoxia. Cyanosis ● Dyspnea and tachypnea.
most commonly results from decreased oxygen satura- ● Lethargy.
tion of normal hemoglobin. Only rarely it results from ● Anorexia/vomiting.
abnormal hemoglobin with decreased oxygen-carrying ● Posterior paresis.
capacity. Hypoxia producing cyanosis results either from ● Abnormal heart sounds.
central (cardiac or respiratory) or peripheral causes.
See main reference on page 128 for details (The Cat
With Abnormal Heart Sounds and/or an Enlarged Heart).
WHERE?
Clinical signs
Hypoxia (i.e. decreased oxygen saturation of normal
hemoglobin). Dyspnea and tachypnea, or in severe cases open-
mouthed breathing, occur because of pleural effusion
Central hypoxia results from congenital cardiac and/or pulmonary edema.
anomalies such as tetralogy of Fallot and pulmonary
arterial hypertension secondary to a large PDA, VSD, Lethargy, anorexia and occasional vomiting may be
ASD or truncus arteriosus, respiratory diseases present.
including tracheal and laryngeal neoplasia (rare), pleu- Occasionally, acute onset of posterior paresis occurs with
ral effusions, pulmonary edema, pneumonia, thoracic painful hardening of the quadriceps and gastrocnemius
wall lesions and rupture of the diaphragm. groups of muscles, cyanosis of the nail beds and cold
Peripheral hypoxia is either generalized as a result of extremities associated with aortic thromboembolism.
generalized vasoconstriction due to hypothermia, heart
failure or shock or localized as a result of arterial or Diagnosis
venous obstruction. Acute arterial obstruction may
Thoracic radiography may show cardiac enlargement,
result from thromboembolism or thrombosis occurring
pleural effusion and pulmonary edema.
with cardiomyopathy, bacterial endocarditis, hyperco-
agulable conditions and cold agglutinin disease. Echocardiography may show left ventricular hypertro-
Venous obstruction occurs as a result of throm- phy and left atrial enlargement in hypertrophic car-
bophlebitis and restrictive devices such as a rubber diomyopathy or left atrial and ventricular dilation with
band around the limb. reduced contractility in dilated cardiomyopathy.

Abnormal hemoglobin with decreased oxygen-
carrying capacity. DIROFILARIASIS**

Classical signs
WHAT?
● Most cats are asymptomatic.
In the cat, the commonest causes of cyanosis include ● Cough, lethargy, anorexia, vomiting,
bronchial and pulmonary disease, pleural effusions, dyspnea and syncope.
cardiac disease, mediastinal neoplasia, diaphragmatic ● Acute dyspnea and sudden death.
hernias and poisoning with acetaminophen. Peripheral
cyanosis is usually the result of arterial thromboem- See main reference on page 104 for details (The
bolism. Coughing Cat).