Amount &
Composition of body
fluids
Fundamental Concepts
 Approximately 60% of the
weight of a typical adult consists
of fluid (water and electrolytes).
 Factors that influence the
Body Fluids
amount of body fluid are age,
gender, and body fat.
 People who are obese have less
fluid than those who are thin.
 Muscle, skin, and blood have the
highest amount of water.
Intracellular
Extracellular
Fluid
Compartments
2 fluid compartments:
 intracellular space (fluid in the cells)
 extracellular space (fluid outside the cells).
Intravascular
Fluid
Fluid
Compartments
Compartments
ECF
Interstitial
ICF
Transcellular
Intravascular
Space
 Approximately
3L
of the average 6 L of blood
volume is made up of plasma.
 The remaining
3L
is made up of erythrocytes,
leukocytes, and thrombocytes.
Interstitial
Space
 The interstitial space contains the fluid that
surrounds the cell and totals about
12 L
in an adult.
 Lymph is an interstitial fluid.
11 to
 smallest division of the ECF compartment
 contains approximately 1 L
Transcellular
space
 include cerebrospinal, pericardial, synovial,
intraocular, and pleural fluids; sweat; and digestive
secretions.
 ECF transports electrolytes; it also carries other
substances, such as enzymes and hormones.
Third-Space
Fluid Shift
 Loss of ECF into a space that does not contribute to
equilibrium
Electrolytes
Fundamental Concepts
 electrically charged molecules or ions that are found
inside and outside the cells of the body
 These ions contribute to the concentration of body
solutions and move between the intracellular and
extracellular environments.
 electrolyte concentration in the body is expressed in
Electrolytes
terms of
milliequivalents
(mEq)
per liter, a measure of chemical
activity
major cations major anions
Electrolytes
•
•
•
•
•
Sodium
Potassium
Calcium
Magnesium
hydrogen ions
•
•
•
•
•
Chloride
Bicarbonate
Phosphate
Sulfate
proteinate ions
sodium (Na+)
 The major cation in extracellular fluid
 plays a major role in fluid regulation.
 As sodium is absorbed, water usually follows by osmosis.
Electrolytes
potassium (K+)
 plays a critical role by influencing the resting membrane potential, which strongly affects cells that
are electrically excitable, such as nerve and muscle cells.
 Increased or decreased levels of K+ can cause depolarization or hyperpolarization of cells, resulting
in hyperactivity or inactivity of tissues such as muscles
 Normal movement of fluids through the capillary wall
into the tissues depends on
Electrolytes
hydrostatic
pressure
(the pressure exerted
by the fluid on the walls of the blood vessel) and the
osmotic pressure exerted by the protein of plasma.
 The direction of fluid movement depends on the
differences in these two opposing forces (hydrostatic
versus osmotic pressure).
Regulation of body
Fluid compartments
Fluid & Electrolytes
Methods of Fluid & Electrolyte Movement
Diffusion
Osmosis
Active Transport
Filtration
Facilitated Diffusion
Osmosis
Osmosis and
Osmolality
- water
movement
across a membrane from an area of
low concentration to an area of high
concentration
 The magnitude of this force depends on the number of
particles dissolved in the solutions, not on their weights.
 The number of dissolved particles contained in a unit of fluid
determines the osmolality of a solution, which influences the
movement of fluid between the fluid compartments
Osmosis and
Osmolality
 Three other terms are associated with osmosis:
osmotic pressure
oncotic pressure
osmotic diuresis
,
, and
.
 Osmotic pressure is the amount of hydrostatic
pressure needed to stop the flow of water by osmosis. It
is primarily determined by the concentration of
solutes.
Osmosis
 Oncotic pressure is the osmotic pressure exerted by
proteins (eg, albumin).
 Osmotic diuresis is the increase in urine output
caused by the excretion of substances such as glucose,
mannitol, or contrast agents in the urine
 the ability of all the solutes to cause an osmotic driving
force that promotes water movement from one
compartment to another.
Tonicity
 The control of tonicity determines the normal state of
cellular hydration and cell size
 ISOTONIC, HYPOTONIC, HYPERTONIC
 ISO - means alike
Isotonic
membrane
have established equilibrium
Solution
 Means that solutions on both sides of selectively permeable
 Any solution put into body with the same osmolality as blood
plasma - 0.9% sodium chloride or 5% glucose
 Solution of lower osmotic pressure
 Less salt or more water than isotonic
Hypotonic
( can swell
& burst )
Solution
 If infused into blood, RBCs draw water into cells
 Solutions move into cells causing them to
enlarge
 Solution of higher osmotic pressure
Hypertonic
 If infused into blood, water moves out of cells &
Solution
into solution (cells wrinkle or shrivel)
 3% sodium chloride is example
 Solutions pull fluid from cells
 is the natural tendency of a substance to move from an area of higher concentration to one of lower
concentration
 It occurs through the random movement of ions and molecules
 Ex. exchange of oxygen and carbon dioxide between the pulmonary capillaries and alveoli and the
tendency
Diffusion
 Involves carrier system that moves substance across a
membrane faster than it would with simple diffusion
Facilitated
Diffusion
 Substance can only move from area of higher
concentration to one of lower concentration
 Ex. movement of glucose with assistance of insulin
across cell membrane into cell
 Hydrostatic pressure in the capillaries tends to filter fluid
out of the intravascular compartment into the interstitial fluid.
 Movement of water and solutes occurs from an area of high
hydrostatic pressure to an area of low hydrostatic pressure.
Filtration
 Ex. The kidneys filter approximately 180 L of plasma per day.
 Ex. passage of water and electrolytes from the arterial
capillary bed to the interstitial fluid; in this instance, the
hydrostatic pressure results from the pumping action of the
heart
 Moves molecules or ions uphill
against concentration & osmotic
pressure
 Hydrolysis of adenosine
Active
Transport
triphosphate (ATP) provides
energy needed
 Requires specific “carrier”
molecule as well as specific
enzyme (ATPase)
 Eg. Sodium-Potassium Pump
Systemic routes of
gains and losses
Fluid and Electrolyte Balance
 The usual daily urine volume in the adult is 1 to 2 L.
Kidneys
 general rule: output is approximately 1 mL of urine per
kilogram of body weight per hour (1 mL/kg/h) in all
age groups.
 Sensible perspiration refers to visible water and
electrolyte loss through the skin (sweating).
 The chief solutes in sweat are sodium, chloride, and
potassium.
 Actual sweat losses can vary from 0 to 1000 mL or
Skin
more every hour, depending on factors such as the
environmental temperature.
 Continuous water loss by evaporation (approximately
600 mL/day) occurs through the skin as insensible
perspiration, a nonvisible form of water loss. Fever
greatly increases insensible water loss through the
lungs and the skin, as does loss of the natural skin
barrier (eg, through major burns).
 normally eliminate water
Lungs
vapor (insensible loss) at a
rate of approximately 300 mL
every day.
 The loss is much greater with
increased respiratory rate or
depth, or in a dry climate.
Gastrointestina
l Tract
 The usual loss through the GI tract is 100 to 200 mL
daily,
Laboratory tests for
evaluation fluid status
Fluid and Electrolyte Balance
Osmolality
 the concentration of fluid that affects the movement of
water between fluid compartments by osmosis.
 measures the solute concentration per kilogram in
blood and urine.
Lab Tests
 is also a measure of a solution’s ability to create
osmotic pressure and affect the movement of water.
 Urine osmolality is determined by urea, creatinine, and
uric acid.
 Osmolality is reported as milliosmoles per kilogram of
water (mOsm/kg)
 serum osmolality - 280 to 300 mOsm/kg
* Estimate: double the
sodium level or:
Osmolality
 urine osmolality - 200 to 800 mOsm/kg
 another term that describes the concentration of
solutions
Osmolarity
 measured in milliosmoles per liter (mOsm/L).
 osmolality is used more often in clinical practice.
 The calculated value usually is within 10 mOsm of the
measured osmolality.
 measures the kidneys’ ability to excrete or conserve
water.
1.010 to
1.025
 normal range:
Urine specific
gravity
.
 varies inversely with urine volume; normally, the larger
the volume of urine, the lower the specific gravity is.
 a less reliable indicator of concentration than urine
osmolality
 increased glucose or protein in urine can cause a
 made up of urea, which is an end product of the metabolism of
protein (from both muscle and dietary intake) by the liver.
 Amino acid breakdown produces large amounts of ammonia
molecules, which are absorbed into the bloodstream.
BUN (Blood
Urea Nitrogen)
 Ammonia molecules are converted to urea and excreted in the
urine.
: 10 to 20 mg/dL
(3.6 to 7.2 mmol/L)
 Normal range
.
 end product of muscle metabolism
 a better indicator of renal function than BUN because it
does not vary with protein intake and metabolic state.
0.7 to 1.4
mg/dL (62 to 124
mmol/L)
 Normal range: approximately
Creatinine
 concentration depends on lean body mass and varies
from person to person.
 Serum creatinine levels increase when renal function
decreases.
 measures the volume percentage of red blood cells
(erythrocytes) in whole blood
 Normal range:
Hematocrit
42% to 52%
35% to 47%
for males
for females
 Conditions that increase the hematocrit value :
dehydration and polycythemia
 decrease hematocrit : overhydration and anemia
 As sodium intake increases, excretion increases; as the
circulating fluid volume decreases, sodium is conserved.
75 to
200 mEq/24 hours (75
to 200 mmol/24
hours)
 Normal urine sodium levels range from
Urine Sodium
.
 A random specimen usually contains more than 40 mEq/L of
sodium.
 Urine sodium levels are used to assess volume status and are
useful in the diagnosis of hyponatremia and acute renal
failure.
Homeostatic
mechanisms
Fluid and Electrolyte Balance
 kidneys normally filter
Kidney
Functions
180 L
1 to 2
of plasma
every day in the adult and excrete
L
of urine.
 They act both autonomously and in response to
bloodborne messengers, such as aldosterone and
antidiuretic hormone (ADH)
 Major functions in fluid balance:
 Regulation of ECF volume and osmolality by selective
retention and excretion of body fluids
 Regulation of normal electrolyte levels in the ECF by
Kidneys
selective electrolyte retention and excretion
 Regulation of pH of the ECF by retention of hydrogen
ions
 Excretion of metabolic wastes and toxic substances
 The pumping action of the heart circulates blood
Heart and
Blood Vessel
Functions
through the kidneys under sufficient pressure to allow
for urine formation.
 Failure interferes with renal perfusion and thus with
water and electrolyte regulation.
Through exhalation, the lungs remove
Lung Functions
approximately 300
mL of water daily in the
normal adult.
Also play a major role in maintaining acid–base
balance.
 Functions of ADH include:
Pituitary
Functions
 maintaining the osmotic pressure of the cells by
controlling the retention or excretion of water by the
kidneys
 regulating blood volume
Aldosterone
 mineralocorticoid
 Increased secretion causes sodium retention (and thus water
retention) and potassium loss.
 decreased secretion causes sodium and water loss and
Adrenal
Functions
potassium retention.
Cortisol
 adrenocortical hormone
 has less mineralocorticoid action
 when secreted in large quantities (or administered as
corticosteroid therapy), can produce sodium and fluid
retention.
 regulate calcium and phosphate balance by means of
Parathyroid
Functions
parathyroid hormone (PTH).
 PTH influences bone resorption, calcium absorption
from the intestines, and calcium reabsorption from the
renal tubules.
Baroreceptors
 located in the left atrium and the carotid and aortic
Other
Mechanisms
arches.
 As arterial pressure decreases, baroreceptors transmit
fewer impulses from the carotid and the aortic arches
to the vasomotor center.
Baroreceptors
stimulates the
sympathetic nervous
system
increase in cardiac
rate, conduction, and
contractility
increase in circulating
blood volume.
decrease in impulse
inhibits the
parasympathetic
nervous system.
Constriction of renal
arterioles
Baroreceptors
Sympathetic
stimulation
increases the release
of aldosterone
decreases glomerular
filtration and increases
sodium and water
reabsorption.
Antidiuretic Hormone and Thirst
 Oral intake is controlled by the
thirst center located in the
hypothalamus
Other
Mechanisms
 The presence or absence of
ADH is the most significant
factor in determining whether
the urine that is excreted is
concentrated or dilute.
serum concentration
or osmolality
increases and blood
volume decreases
neurons in the
hypothalamus are
stimulated by
intracellular
dehydration
person increases his
or her intake of oral
fluids.
thirst occurs
Other
Mechanisms
Osmorecepto
rs
 Located on the surface of the hypothalamus,
osmoreceptors sense changes in sodium concentration.
osmotic pressure
increases
neurons become
Osmoreceptors
dehydrated
quickly release
impulses to the
posterior pituitary
ADH alters
permeability to
water
ADH travels in the
blood to kidneys
Increases the release
of ADH
causing increased
reabsorption of
water and decreased
urine output.
Atrial Natriuretic
Peptide
 also called atrial natriuretic factor
Other
Mechanisms
 a peptide synthesized, stored, and released by muscle cells of
the atria of the heart in response to several factors.
 These factors include:
 increased atrial pressure
 angiotensin II stimulation
 endothelin (a powerful vasoconstrictor of vascular smooth
muscle peptide released from damaged endothelial cells in
the kidneys or other tissues)
 sympathetic stimulation
 any condition that results in
Atrial
Natriuretic
Peptide
volume expansion, hypoxia, or
increased cardiac filling
pressures increases the release of
ANP.
 The action of ANP is the direct
opposite of the reninangiotensin–aldosterone system;
ANP decreases blood pressure
and volume
Calculations
Calculate the flow rate using standard formula
Standard Formula:
Rate
=
Volume (cc) x gtt factor (gtts/cc)
Duration (hrs) x 60 min/hr
Duration
=
Volume (cc) x gtt factor (cc)
Rate (gtt/min) x 60 min/hr
If ml/hr is known:
ml/hr X drop factor
60 min
 The physician’s order reads “Administer D5LR 3L for 24
hrs”
a. To how many gtts/min will you regulate the IVF?
b. How many mls/hr will be infused?
Order: 1000 ml of D5NSS to infuse over 12 hours
Available: macrodrip set with 10 gtts/ml
a. gtts/min?
100 cc/hr
gtts/min? (Baxter/macroset)
PNSS 1L @ 120 gtts/min (Abbott)
Hours to run?
 A liter of IV fluid was started @ 9 AM and was to infuse
for 8 hours. The IV set delivers 10 gtt/ml. Four hours
later only 400 ml were absorbed.
a.
How much IV fluid was left?
b.
Recalculate the flow rate for the remaining IV
fluids.