الفهرس 
Physiology of water balance
Daily Loss of Body WaterOnly 14 pages are availabe for public view
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Abstract
The relative constancy of the body fluids is remarkable
because there is continuous exchange of fluid and solutes
with the external environment, as well as within the different
body compartments. Intake of water is highly variable among
different people and even within the same person on different
days, depending on climate, habits, and level of physical
activity.
The kidneys are faced with the task of adjusting the
excretion rate of water and electrolytes to match precisely the
intake of these substances, as well as compensating for
excessive losses of fluids and electrolytes that occur in
certain disease states.
Blood contains both extracellular fluid (the fluid in
plasma) and intracellular fluid (the fluid in the red blood
cells) .
The distribution of fluid between intracellular and
extracellular compartments, in contrast, is determined mainly
by the osmotic effect of the smaller solutes especially
sodium, chloride, and other electrolytes acting across the cell
membrane .The osmolal concentration of a solution is
called osmolality when the concentration is expressed
as osmoles per kilogram of water, it is called osmolarity
when it is expressed as osmoles per liter of solution .
If a cell is placed into a hypotonic solution, water will
diffuse into the cell, causing it to swell; water will continue
to diffuse into the cell, diluting the intracellular fluid while
also concentrating the extracellular fluid until both solutions
have about the same osmolarity. Solutions of sodium
chloride with a concentration of less than 0.9 percent are
hypotonic and cause cells to swell. If a cell is placed in
a hypertonic solution, water will flow out of the cell into the
extracellular fluid, concentrating the intracellular fluid and
diluting the extracellular fluid. In this case, the cell will
shrink until the two concentrations become equal. Sodium
chloride solutions of greater than 0.9 percent are hypertonic .
A measurement that is readily available to the clinician
for evaluating a patient’s fluid status is the plasma sodium
concentration. When plasma sodium concentration is reduced
more than a few milliequivalents below normal (135 - 145
mEq/L), a person is said to have hyponatremia.When plasmasodium concentration is elevated above normal, a person is
said to have hypernatremia .
Hyponatremia is the most common electrolyte disorder
encountered in clinical practice and may occur in up to 15%
to 25% of hospitalized patients .
Some IV fluids are designed to stay in the intravascular
space to increase the intravascular volume, or volume of
circulating blood. Other IV fluids are specifically designed so
the fluid leaves the intravascular space and enters the
interstitial and intracellular spaces .
Echocardiography has the advantage of being noninvasive and it can provide a quick ‗snapshot‘ of the fluid
status of the patient .
Absence of symptoms does not exclude mild to
moderate hypovolemia, especially if the volume loss has
occurred gradually .
The choice of oral or intravenous replacement fluids (or
both) for hypovolemic states is dictated by the integrity of
gastrointestinal absorptive function, by the magnitude of the
volume deficit, and by the disturbances in other electrolyte
and acid-base parameters .In addition to replacement fluids, maintenance fluids
must be provided to counteract ongoing losses. Such ongoing
losses may be a continuation of the underlying disease state
(e.g., continued vomiting, diarrhea, polyuric states, or severe
burns). The volume, rate of administration, and composition
of these replacement fluids are best determined by actual
measurements of the corresponding ongoing fluid losses,
with appropriate adjustments for the patient’s clinical
assessment parameters .
The most important step in hypervolemia management
is ameliorating renal sodium retention by recognition and
treatment of the underlying disease. Three treatment
modalities are available to reduce ECF volume directly by
inducing negative sodium balance: dietary sodium restriction,
diuretics, and extracorporeal fluid removal by ultrafiltration .