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Introduction
Physiologic homeostasis depends on normal fluids and
electrolyte and acid-base balance. Both are required for
normal cellular functions and to sustain life.
Fluid-electrolyte, acid-base balances commonly
accompany illness. Severe imbalances may result in
death. Such imbalances affect not only the acutely and
chronically ill but also clients faulty diets or those who
take selected medications such as diuretics and steroids.
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Body Fluids
Water= most important nutrient for life.
Water= primary body fluid.
Adult weight is 55-60% water.
Loss of 10% body fluid = 8% weight loss SERIOUS
Loss of 20% body fluid = 15% weight loss FATAL
Fluid gained each day should = fluid lost each day
(2 -3L/day average)
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Body Fluid Compartments
About 60% of the adult human body is water.
Most body water is located within cells (intracellular fluid).
The rest is outside cells (extracellular fluid). Extra-cellular fluid includes the water
between cells (interstitial fluid) and in the plasma (serum) portion of blood
(intravascular fluid).
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In healthy adults, oral fluid intake averages about 2500 mL/
day; however, it can range between 1800 and 3000 mL/day,
with a similar volume of fluid loss.
Intake and Output
A standard formula for calculating daily fluid intake
is as follows:
100 mL/kg for the first 10 kg of weight, plus
50 mL/kg for the next 10 kg of weight, plus
15 mL/kg per remaining kilograms of weight
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Intake and Output
The primary sources of body fluid are food
and liquids.
As fluid volume increases, the body loses
fluid, primarily through:
Urination, in a proportionate volume to
maintain or restore equilibrium.
Other mechanisms of fluid loss include
bowel elimination, perspiration, and
breathing.
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Intake and Output
Losses from sweat and the vapor in exhaled air are
referred to as insensible losses because they are, for
practical purposes, unnoticeable and unmeasurable
Percentage of Body Fluids According to
Age and Sex
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Regulation of Fluids
Hypothalmus –thirst receptors (osmoreceptors)
continuosly monitor serum osmolarity
(concentration). If it rises, thirst mechanism is
triggered.
+Vasopressin (AKA ADH )– increasing H20
reabsorption
Pituitary regulation- posterior pituitary releases
ADH (antidiuretic hormone) in response to
increasing serum osmolarity. Causes renal
tubules to retain H20.
Thirst is a late sign of water deficit
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Renal regulation- Nephron receptors sense decreased
pressure (low osmolarity) and kidney secretes RENIN.
Renin – Angiotensin I – Angiotensin II
Angiotensin II causes Na and H20 retention by kidneys
AND…..
Stimulates Adrenal Cortex to secrete Aldosterone which
causes kidneys kidneys to excrete K and retain Na and H20.
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● Age variations exist in regards to H20 content of fluid
compartments
● Infants =
60% of H20 is found in ECF
40% of H20 is found in ICF
● What might this mean in regards to fluid loss for an
infant?
Reverse of adults!
Infant MORE PRONE to fluid LOSS!
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Distribution of Fluids and Electrolytes
Translocation (movement back and forth) of fluid and exchange of
chemicals including electrolytes, acids, and bases is continuous in and
among all areas where water is
located.
Physiologic processes govern the movement and relocation of fluids and
chemicals at the cellular level. These processes include:
osmosis,
filtration,
Diffusion
active transport.
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Active Transport
Active transport requires an energy source, a substance called
adenosine triphosphate (ATP), to drive dissolved chemicals from
an area of low concentration to an area of higher concentration
the opposite of passive diffusion.
Its function is to move potassium from lower concentrations in
the extracellular fluid into cells where potassium is highly
concentrated.
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Solvent (H20) Movement
Cell membranes are semipermeable allowing water
to pass through
Osmosis- major way fluids transported Water shifts
from low solute concentration to high solute
concentration to reach homeostasis (balance).
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Osmolality
Concentration of particles in solution
The greater the concentration (Osmolarity) of a solution, the greater
the pulling force (Osmotic pressure)
Normal serum (blood) osmolarity = 280-295 mOSM/kg
A solution that has HIGH osmolarity is one that is > serum osmolarity =
HYPERTONIC solution
A solution that has LOW osmolarity is one that is < serum osmolarity =
HYPOTONIC solution
A solution that has equal osmolarity as serum = ISOTONIC solution
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Hypertonic Fluids
Hypertonic fluids have a higher concentration
of particles (high osmolality) than ICF
This higher osmotic pressure shifts fluid from
the cells into the ECF
Therefore Cells placed in a hypertonic
solution will shrink
