Page 565 - Problem-Based Feline Medicine

25 – THE CAT WITH POLYCYTHEMIA 557

Accompanying clinical signs are attributable to the
DISEASES CAUSING POLYCYTHEMIA
cause of the dehydration. Renal and gastrointestinal
tract fluid losses are common causes of dehydration,
DEHYDRATION*** and present with polyuria and polydipsia, or vomiting
and diarrhea, respectively, coupled with inadequate
Classical signs fluid intake.
● Skin tenting. Massive fluid deficits can occur after burns because of
● Tacky mucus membranes. fluid losses from the skin.
● Combination of increased PCV and plasma
Acute viral respiratory disease can cause dehydration
protein concentration.
because of losses from ocular and nasal discharges
● Signs attributable to underlying disease.
and hypersalivation.
Diagnosis
Pathogenesis
Characteristic clinical signs of dehydration are
A relative increase in red cells occurs as a result of accompanied by hemoconcentration, normal blood
dehydration. The increase in red cell concentration is oxygen saturation and increased total plasma pro-
secondary to decreased plasma volume from dehydra- tein concentration.
tion. Total red cell mass is normal, although red cell
mass can only be determined using radio-isotope-
Differential diagnosis
tagged autologous red blood cells, a technique not gen-
erally available in practice. Since clinical signs of dehydration are characteristic, dif-
ferential diagnoses mainly refer to the condition caus-
Relative polycythemia occurs most commonly when
ing the dehydration, rather than to dehydration itself.
excessive fluid loss through the gastrointestinal tract
(vomiting or diarrhoea) or kidney (diabetes mellitus
or renal failure) is coupled with inadequate fluid Treatment
intake.
Fluid and electrolyte therapy is initially required to
restore intravascular volume because this is most
Clinical signs critical for survival, and then to replace fluid and elec-
trolytes in the extravascular compartments includ-
Clinical signs of dehydration include skin tenting,
ing both intracellular and interstitial fluid. Many
tacky mucus membranes and high plasma protein
patients that are dehydrated have adequate circulating
levels.
blood volume to maintain tissue perfusion, and do not
● Dehydration is assessed initially by examining skin
need rapid volume expansion.
turgor, usually by drawing the skin at the back of
the neck upward. Of total body water, 2/3 is intracellular and 1/3 is
– It is not until there is 5% dehydration that there extracellular. Only about 1/6 of body water is
is subtle loss of skin elasticity. intravascular.
– At 6–8% dehydration, there is a delay in ● Sodium and chloride are the major electrolytes in
return of the skin to its normal position, the the extracellular fluid.
capillary refill time may be slightly prolonged, ● Potassium and phosphates are the major elec-
and mucous membranes may be dry to touch. trolytes in intracellular fluid.
– At 10–12% dehydration, tented skin stands in
Type of fluid selected should be based on the elec-
place; mucus membranes are dry; the eyes are
trolyte and acid–base status of the cat, and whether it
sunken in the orbits; there is prolonged capillary
is being used for replacement or maintenance.
refill time; and there may be signs of shock.
– By 12–15% dehydration, signs of shock are Crystalloids are the most common types of fluids used,
present and death is imminent. and have sodium as their major osmotically active par-