Page 70 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

60 ELECTROLYTE DISORDERS

vomiting, ataxia, diarrhea, and tremors. These ingredients patients with underlying cardiac disease. Patients with
act as osmotic laxatives, causing a shift in water from the CDIorNDItypicallyarepresentedforevaluationofsevere
tissues into the lumen of the bowel and resulting in polydipsia and polyuria.
hypernatremia. Warm water enemas may facilitate
removal of paintball ingredients from the bowel, but TREATMENT OF
activated charcoal products generally should not be used
because they may contain sorbitol. Depending on the HYPERNATREMIA
duration of onset, 5% dextrose in water (acute onset) or
The main goals in treating patients with hypernatremia
0.45% NaCl (unknown onset) can be administered to
are to replace the water and electrolytes that have been
gradually correct hypernatremia. Parenteral fluids can
lost and, if necessary, to facilitate renal excretion of excess
be supplemented with potassium chloride if serum
sodium. The first priority in treatment should be to
potassium concentration decreases below 2.5 mEq/L.
restore the ECF volume to normal. The next priority is
Therapeutic administration of hyperosmolar solutions
to diagnose and treat the underlying disease responsible
containing large amounts of sodium during cardiac
for the water and electrolyte deficits.
resuscitation can cause hypernatremia and hypertonicity
(e.g., hypertonic saline, sodium bicarbonate). For exam- PURE WATER LOSS
ple, serum sodium concentration reached 174 mEq/L
within 15 minutes after beginning infusion of 7.2% NaCl Total body solute (TBS) is the product of TBW and
2
at a rate of 15 mL/kg in normal beagles. Sodium phos- plasma osmolality (P osm ). If a patient’s fluid loss has been
phate enemas may also result in mild hypernatremia. 3 limited to pure water, the following relationship is true:
Primary hyperaldosteronism also may be associated with
hypernatremia. It is rare in dogs, but several cases TBS presentÞ ¼ TBS previousÞ
ð
ð
have been reported in cats (see Chapter 5 ). Mild TBW presentÞ P osm presentð Þ ¼ TBW previousÞ
ð
ð
hypernatremia also may occur in dogs with
hyperadrenocorticism. 101,128 P osm previousð Þ
CLINICAL SIGNS OF If we assume that body water (TBW) is 60% of body
HYPERNATREMIA weight measured in kilograms (Wt) and that 2.1 P Na
is an estimate of P osm :
The clinical signs of hypernatremia primarily are neuro-
ð
logic and related to osmotic movement of water out of 2:1 P Na presentð Þ 0:6 Wt presentÞ
brain cells. A rapid decrease in brain volume may cause ¼ 2:1 P Na previousð Þ 0:6 Wt previousÞ
ð
rupture of cerebral vessels and focal hemorrhage. The
severity of clinical signs is related more to the rapidity This equation reduces to:
of onset of hypernatremia than to the magnitude of
hypernatremia. In dogs and cats, clinical signs of P Na presentð Þ Wt presentÞ ¼
ð
hypernatremia are observed when the serum sodium P Na previousð Þ Wt previousÞ
ð
concentration exceeds 170 mEq/L. 66,78,84,133 If
hypernatremia develops slowly, the brain has time to adapt P Na ðpresentÞ WtðpresentÞ
to the hypertonic state by production of intracellular WtðpreviousÞ¼
P Na ðpreviousÞ
solutes (e.g., inositol and amino acids) called osmolytes
or idiogenic osmoles. These substances prevent dehy-
The water deficit is the difference between the previous
dration of the brain and allow patients with chronic
and present body weights:
hypernatremia to be relatively asymptomatic.
Where described in dogs and cats, clinical signs of
Wt previousÞ Wt presentÞ ¼
ð
ð
hypernatremia and hypertonicity have included anorexia,
lethargy, vomiting, muscular weakness, behavioral P Na ðpresentÞ WtðpresentÞ WtðpresentÞ
change, disorientation, ataxia, seizures, coma, and P Na ðpreviousÞ
death.* If hypotonic losses are the cause of hypernatremia,
clinical signs of volume depletion (e.g., tachycardia, weak or
pulses, and delayed capillary refill time) may be observed

on physical examination. If hypernatremia has developed P Na ðpresentÞ
WtðpresentÞ 1
as a result of a gain of sodium, signs of volume overload P Na ðpreviousÞ
(e.g., pulmonary edema) may be observed, especially in
Consider a previously normal dog that has been deprived
*References 5, 23, 27, 31, 34, 78, 84, 133, 159. of water for several days. The dog weighs 10 kg at