FLUIDS AND ELECTROLYTES
AMOUNT OF FLUID IN THE BODY:
Fetus – 100%
Baby – 80-85% (no muscles yet)
Adult – 70%
Elderly – 50%
> amount of water taken must be equal to the amount of
water lost
WATER INTAKE
Food and drink – 2300 mL
Cell Metabolism – 200 mL
Total: 2500 mL
OUTPUT
Kidneys – 1800 mL
Skin (sweat) – 300 mL
Lungs (expiration) – 300 mL (ᛏ RR, more fluid lost)
GI Tract (feces) – 100 mL
TOTAL: 2500 mL
FLUID COMPARTMENT
Intracellular – 40% (cytoplasm/protoplasm)
Extracellular – 20%
Intravascular – 5%
o Plasma (light yellow)
o Cellular components (darkish red)
Interstitial - 15% (third space)
MECHANISMS OF FLUID BALANCE
1. ANTI-DIURETIC HORMONE (ADH)
- Stored in the posterior pituitary gland
- Causes renal tubules to reabsorb water so
that kidneys will not form too much urine
- Released when dehydrated
dehydrated > hypothalamus will feel that
there is ᛎ in circulating blood volume >
stimulate post. pituitary gland to release
ADH > ADH will have an effect on the renal
tubules to reabsorb water >> ᛎ urine output
no reabsorption of NA
>> output is less because body is compensating after surgery
2. THIRST MECHANISM
- Compensatory mechanism
perspire > excrete lots of body fluids > thirst
center in the brain (hypothalamus) will be
stimulated > tells us to drink water
ᛎ blood volume (d/t vomiting, diarrhea, etc)
will cause ᛎ BP > ᛎ BP = less blood going to
the kidneys > kidneys will compensate by
releasing renin > RAAS mechanism >
angiotensin 2 > angiotensin 2 stimulates
thirst center
- thirst mechanism MAY NOT work (ex. Patient is
unconscious)
- unconscious patient should receive IV fluids (N/I: do not
slow down)
FLUID INGESTION
Stretch receptors (stomach & intestine) will
send inhibitory signals to the thirst center
Thirst mechanism will stop if stomach and
intestines are stretched (by eating)
3. ALDOSTERONE
- From the adrenal cortex
- Causes reabsorption of NA > water follows
- Hypovolemia > RAAM
hypovolemia (d/t bleeding/vomiting) >
there will be ᛎ in circulating blood volume =
priority is primary organs = less blood to
secondary organs > kidney will compensate
by releasing renin > renin goes to liver and
converts a precursor protein
(angiotensinogen) to angiotensin 1 (mild
vasoconstrictor) > angiotensin 1 goes to
lungs and converts ACE to angiotensin 2
(potent vasoconstrictor) > angiotensin 2 >
produce aldosterone > reabsorb NA >>
water retention > ᛏ BP
4. SYMPATHETIC STIMULATION (SNS)
- ᛎ in blood volume > ᛎ BP > SNS is stimulated
> trigger adrenal glands > adrenal medulla >
epinephrine and norepinephrine will be
released
Epinephrine – causes ᛏ in cardiac rate > more blood
will be pumped by the heart > more blood will go to
the different organs of the body
Norepinephrine – will cause vasoconstriction, ∴ ᛏ
BP → more blood will go to the priority organ (brain)
** if less blood is going to the kidneys > less oxygen and
nutrients > less urine
If there is vasoconstriction, assess:
Pale and cold skin – because blood is being
directed to the brain
ATRIAL NATRIURETIC PEPTIDE
- cardiac hormone stored in the cells of the atria
- released when atrial pressure is increased
