Page 126 - Problem-Based Feline Medicine

118 PART 2 CAT WITH LOWER RESPIRATORY TRACT OR CARDIAC SIGNS

Diagnosis Pathogenesis

Diagnosis is based on clinical signs together with Peripheral hypoxia occurs due to vasoconstriction as
anesthetic records indicating drug overdose, or a a consequence of hypovolemic, cardiogenic or septic
history of access to sedative, narcotic or anesthetic shock or due to hypothermia. This leads to inade-
drugs. quate capillary perfusion and oxygen delivery to
peripheral tissues becomes impaired, which may lead
to generalized peripheral cyanosis.
CENTRAL NERVOUS SYSTEM DAMAGE Hypovolemia occurs when blood volume is diminished
TO THE RESPIRATORY CENTER by whole blood loss or by extracellular fluid losses.
Compensatory mechanisms include splenic and venous
Classical signs constriction to translocate blood from the venous
● Persistent or episodic weakness. capacitance vessels to the central arterial circulation;
● Cheyne–Stokes respiration. arteriolar constriction to maintain diastolic blood pres-
● Cyanosis. sure and increasing heart rate to increase cardiac out-
put. When severe, hypovolemic shock ensues resulting
in generalized peripheral hypoxia.

Clinical signs Cardiogenic shock occurs with any condition that
interferes with forward outflow from the heart to
Central respiratory depression as a result of CNS such an extent that adequate tissue perfusion is not
infection, increased intracranial pressure or head achieved. Examples include acute or chronic heart fail-
injury leads to slow, gasping respirations (Cheyne– ure, cardiomyopathy, intracardiac thrombosis, pericar-
Stokes respiration). dial tamponade, heartworm disease and severe
The cat may be unconscious and cyanotic. arrhythmias.
Other evidence of trauma, or neurologic deficits may be When an animal’s blood has become infected by bac-
present. teria, viruses, rickettsia, fungi or protozoa it is con-
sidered septic. Some of these organisms produce
toxins which are directly vasoactive or release vasoac-
tive substances. When the infection is affecting the ani-
Diagnosis mal to the extent that tissue perfusion is compromised,
Neurological examination demonstrates neurologic septic shock has ensued.
deficits consistent with a medullary lesion together Hypothermia results when heat loss exceeds heat pro-
with a typical respiratory pattern. duction. Decreasing body temperature decreases the
partial pressure of oxygen, increases solubility and
shifts the oxygen–hemoglobin dissociation curve to the
PERIPHERAL HYPOXIA – left. These changes impede oxygen unloading at the tis-
GENERALIZED sue level. Thermoregulatory vasoconstriction further
decreases oxygen delivery.

VASOCONSTRICTION*
Clinical signs
Classical signs
Generalized cyanosis together with signs of severe
● Generalized cyanosis. hypovolemia, severe cardiac disease, hypothermia
● Signs of hypovolemic, cardiogenic, or septic or sepsis, which suggest vasoconstriction is leading to
shock or hypothermia. inadequate capillary perfusion and impaired oxygen
delivery to peripheral tissues.