clinica saunders

clinica saunders


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or less) in the presence of dehydration.
It theoretically occurs as solute is lost in excess of the
concentration found in normal serum (hypertonic
loss), but this is probably not the most significant
mechanism. More likely, it is the loss of isotonic fluid
and concurrent intake and absorption of hypotonic
fluids (such as drinking of water) with the net dilu-
tional effect on the remaining extracellular sodium
concentration below normal.
Detection of Dehydration
Clinical tools to detect dehydration are limited in both
sensitivity and specificity. There is no single test or pro-
cedure to accurately assess the magnitude of dehydra-
tion. Integration of historical findings, abnormalities on
physical examination, and laboratory measurements
will be necessary to quantify dehydration. Dehydration
is not detectable by clinical means until approximately
5% of body weight in water has been lost. An acute loss
of greater than 12% body weight in water is considered
life threatening (Table 5-3).
History
History often leads the clinician to suspect dehydration
and to assess its magnitude more accurately. Question
Table 5-3. PERCENTAGES OF DETECTABLE
DEHYDRATION
Dehydration Signs
<5% Not detectable on physical exam; history is 
suggestive of losses; acute body weight 
changes
5% Subtle loss of skin elasticity
6\u20138% Mild delay of skin tent, slight prolongation of 
CRT, dry mucous membranes
8\u201310% Obvious delay of skin tent, slight prolongation 
of CRT, dry mucous membranes, eyes slightly 
sunken in orbits
10\u201312% Severe prolongation of skin tent, eyes sunken in 
orbits, dry mucous membranes, signs of shock 
likely present (prolonged CRT, tachycardia, 
weak pulses etc.)
>12% Moribund
*CRT, capillary refill time.
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86 Section 1 / Patient Management
the owner about volume of intake (adipsia, hypodipsia,
polydipsia, or normal intake of water). Because volume
of water intake may, in part, be a function stimulated by
food intake, note also the presence or absence of
anorexia. Abnormal losses of body fluid may be deter-
mined from owner responses to questions about vomit-
ing, diarrhea, polyuria, panting, excessive salivation, or
other bodily discharge. The duration of these historical
signs and the magnitude of losses affect the magnitude
of clinically detectable dehydration.
Physical Examination
Physical examination provides general guidelines for
detecting dehydration but is subjective (see Table 5-3).
Signs of listlessness and depression may occur from
dehydration but may be partially attributable to the
underlying disease or to concomitant electrolyte and
acid-base abnormalities. As dehydration becomes more
severe, decreased skin turgor, sunken eyes, dryness of
mucous membranes, tachycardia, diminished capillary
refill, and signs of shock may occur. An accurate and
recent body weight, when available, can be used for
comparison to evaluate change in body weight as an
indicator of body water change.
\ufffd Key Point An acute increase or decrease in an
animal\u2019s body weight often reflects acute gain or
loss of body water. This is the most sensitive 
clinical tool for assessment of dehydration and
rehydration. An acute loss or gain of 1 kg is the
equivalent of losing or gaining 1 L of fluid.
Skin Turgor
Skin turgor assessment during physical examination is
important for estimating the percentage of body weight
loss due to dehydration. Skin turgor is evaluated by
determining the time required for skin gently lifted
from the body to return to its original position (referred
to as the skin pinch or skin tent). Normal skin pliabil-
ity (skin turgor) depends on hydration of the tissues in
the area tested. Skin turgor is largely determined by
hydration status of the interstitial tissues, although both
vascular and intracellular hydration also contribute.
Elastin and adipose within skin and subcutaneous
tissues will also influence the apparent skin turgor.
Choose skin from the trunk as a test area. Avoid depen-
dent areas and skin from the neck. Normal skin returns
immediately to its initial position when lifted a short dis-
tance and released. Dehydrated skin shows varying
degrees of slow return to the original position. As dehy-
dration progresses, the time required for the return of
the skin pinch to its initial position becomes greater.
The clinician assigns increasing percentages of dehy-
dration to abnormal skin turgor of increasing severity
(see Table 5-3).
Skin Turgor Artifacts
Many artifacts confuse interpretation of skin turgor.
\u2022 Skin turgor of obese animals may appear normal
despite dehydration, owing to the large amounts of
subcutaneous fat.
\u2022 The skin of an emaciated animal with normal hydra-
tion may fail to return to its normal position owing
to a lack of subcutaneous fat and elastic tissue. Con-
sequently, underestimating dehydration in obese
animals and overestimating dehydration in emaci-
ated animals can occur.
\u2022 Avoid testing cervical skin because redundant skin in
the neck area confuses the result.
\u2022 Skin turgor changes in longhaired animals are more
difficult to detect than those in shorthaired animals.
\u2022 Differences in turgor assessment can occur in the
same animal in the standing versus recumbent 
positions.
\ufffd Key Point Dehydration may be as much as 5% of
body weight loss in lean dogs and 10% or more 
in obese dogs before loss of skin turgor is 
detected.
Other Physical Examination Artifacts
\u2022 Dry mucous membranes may occur in animals that
pant continually and in those given anticholinergics.
\u2022 Sunken eyes may be seen with catabolic diseases that
decrease the soft tissue behind the globe or with
atrophy of the muscles of mastication.
\ufffd Key Point Assessment of fluid, electrolyte, and acid-
base status will frequently be in error if only the
history and physical examination are available for
interpretation. The more seriously ill an animal is,
the more important evaluation of laboratory data
becomes.
Laboratory Assessment of Dehydration
Packed Cell Volume and Total Plasma Protein
Simple laboratory testing is helpful in evaluation of
intravascular hydration. Packed cell volume (PCV)
recorded in percentages (SI unit: L/L) and total plasma
protein (TPP) recorded in gm/dl (SI unit: g/L) can be
rapidly and inexpensively determined using microhe-
matocrit tubes and a refractometer. These two tests
require only a few drops of blood and can be taken by
capillary action from a 25-gauge venipuncture. TPP 
concentration may be more helpful in the detection of
dehydration than PCV. Increased TPP and PCV provide
documentation for intravascular dehydration. Simulta-
neous evaluation of PCV and TPP is recommended 
in order to minimize interpretation errors due to pre-
existing anemia or hypoproteinemia. (Table 5-4) Addi-
tional value is obtained when PCV and TPP are followed
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Chapter 5 / Fluid Therapy for Dogs and Cats 87
Anticipation of Dehydration with Specific Diseases
Dehydration should be anticipated in sick animals with
certain disease syndromes known to predispose a
patient to dehydration regardless of physical exam or
laboratory findings. For example, a collapsed diabetic is
very likely to be dehydrated, as is an animal with
advanced chronic renal failure or a patient with upper
intestinal obstruction.
Correction (Replacement) of Dehydration
The volume of fluid to be replaced is calculated as follows
based on the assessed percentage of dehydration and
the patient\u2019s present body weight:
\u2022 % dehydration ¥ weight (kg) = L of fluid to be
replaced.
\u2022 % dehydration ¥ weight (lbs) ¥ 500 = ml of fluid to
be replaced.
\u2022 Alternatively, if a known recent body weight is avail-
able for comparison, replace 1 L of fluid for every
kilogram (500 ml/lb) of acute body weight loss.
\u2022 The type of fluid
Bruno
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