Download DEHYDRATION A disturbance of body water balance in which more

DEHYDRATION
A disturbance of body water balance in which more fluid is lost from the body
than is absorbed results in reduction in circulating blood volume and in dehydration
of the tissues.
Electrolyte imbalances occur commonly as a result of loss o f electrolytes,
or relative changes in concentrations due to loss of water.
Common electrolyte imbalances include hyponatremia, hypokalemia, hypocalcemia
and hypochloremia.
Acid-base imbalances, either acidemia or alkalemia, occur as a result of the addition
of acid and depletion of alkali reserve, or the loss of acid with a relative increase in alkali
reserve.
ETIOLOGY:
There are two major causes of dehydration:
1. Inadequate water intake
Deprivation of water, a lack of thirst due to toxemia, and the inability to drink
water as in esophageal obstruction.
2. Excessive fluid loss.
Diarrhea is the most common reason for excessive fluid loss, although vomiting,
polyuria and loss of fluid from extensive skin wounds or by copious sweating may be
important in sporadic cases.
Severe dehydration also occurs in acute carbohydrate engorgement in ruminants,
acute intestinal obstruction and diffuse peritonitis in all species, and in dilatation and
volvulus of the abomasum.
PATHOGENESIS
Two factors are involved in the pathogenesis of dehydration:
1. Depression of tissue water content with resulting interference in tissue
metabolism.
2. Reduction in the free water content of blood.
The initial response to negative water balance is the withdrawal of fluid
from the tissues and the maintenance of normal blood volume.
The fluid is drained primarily from the intracellular and interstitial fluid spaces.
Essential organs including the central nervous system, heart and skeleton the
major loss occurs from connective tissue, muscle and skin.
The loss of fluid from the interstitial and intracellular spaces results in loss of
skin elasticity, dryness of the skin and mucosa, and a reduction and
retraction of the eyeball (enophthalmia) due to reduction in the volume of the
postorbital fat deposits.
Dehydration exerts important effects on tissue metabolism.
There is an increase in breakdown of fat, then carbohydrate and finally protein, to
produce water of metabolism. The increased endogenous metabolism under relatively
anaerobic conditions results in the formation of acid metabolites and the development
of metabolic acidosis.
Urine formation decreases because of the restriction of renal blood flow
and this, together with the increased endogenous metabolism, causes a moderate
increase in blood levels of nonprotein nitrogen.
The body temperature may increase slightly initially – dehydration hyperthermia
- because of insufficient fluid to maintain the loss of heat by evaporation.
CLINICAL FINDINGS
The first and most important clinical finding in dehydration is
1-Dryness and wrinkling of the skin, giving the body and face a
shrunken appearance. The eyes recede into the sockets and the skin
subsides slowly after being picked up into a fold ( Sunken eyes ) .
2-The second best indicator of hydration status in calves is the elasticity
of the skin of the neck and lateral thorax, which are assessed by
pinching the skin between the fingers, rotating the skin fold 90° and
noting the time required after release of the skin fold for the skin fold to
disappear (normally < 2 s) .
CLINICAL PATHOLOGY
Dehydration is characterized by an increase in the packed cell volume and total
serum protein concentration.