SCR 110 Fluid and Electrolyte Notes

FLUIDS, ELECTROLYTES & nutrients to the cells and remove waste product
from them.
ACIDE-BASE 2. Intravascular fluid is the plasma within the blood.
Its main func<on is to transport blood cells.
Body Fluid 3. Transcellular fluid includes specialized fluids, such
• Water is the primary body fluid. as cerebrospinal, pleural, peritoneal, and synovial
• Total body water content varies with age, gender, fluid; and diges<ve juices
and adipose <ssue.
• Water contains solutes
- Electrolytes - substances (e.g., sodium, potassium)
that develop an electrical charge when dissolved in
water
- Nonelectrolytes - substances (e.g., glucose, urea)
that do not conduct electricity
• Func<ons:
- Maintain blood volume.
- Regulate body temperature.
- Transport material to and from cells.
- Serve as a medium for cellular metabolism.
- Assist with diges<on of food. Third Spacing:
- Serve as a medium for excre<ng waste. • The accumula<on of fluid within body cavi<es,
intes<nal areas, or areas of the body that normally
CharacterisBcs of Body Fluids contain li`le fluid.
-> have regulatory mechanisms, which keep them in • Certain condi<ons cause fluid to move into an area
balance for normal func<on. that makes it physiologically unavailable, such as
- A healthy person has a total body water of 50-60% of into the peritoneal space (in ascites), the pericardial
body weight. (Infants have more body fluid 70- 83% space (with pericardial effusion), or into the vesicles
of BW than extracellular fluids (ECF) in adult more (blisters) with a burn wound-> This fluid is literally
prone to fluid deficits) trapped in a third compartment—not within
Fluid amount = Volume. inters<<al or the intravascular spaces.
Fluid concentraBon = Osmolality
Fluid composiBon (electrolyte concentraBon) Electrolytes and Ions
Degree of acidity = pH • Electrolytes
Compounds that separate into ions (charged par<cles)
Body Fluid Compartments (distribuBon) when they dissolve in water. Electrolytes (solutes) are
• Intracellular fluid (ICF) is contained within the cells. dissolved in plasma (solu.on). - The liquid in which a
Essen<al for cell func<on and metabolism, it accounts solute is dissolved is called a solvent.
for approximately 40% of body weight. • Ions (charged par<cles)
• Extracellular fluid (ECF) is outside the cells. ECF - CaBons: posiBvely charged (+): sodium, potassium,
carries water, electrolytes, nutrients, and oxygen to calcium, magnesium
the cells and removes the waste products of cellular - Anions: negaBvely charged (-): chloride,
metabolism. ECF accounts for 20% of body weight. bicarbonate, sulfate.
ECF exists in three main locaBons in the body: - Anions and Ca.ons combine to make salts ( ex.
Table salt: NaCl separate in water into Na+ and Cl-
Extracellular fluid (ECF) Intracellular:
1. IntersBBal fluid lies in the spaces between the Ca<ons: potassium and magnesium
body cells -> a thin layer of fluid which surrounds Anions: phosphate
the body’s cell (Excess fluid within the inters<<al Extracellular:
space is called edema) -> helps bring O2 & Ca<ons: sodium
Anions: chloride

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,Fluid Imbalances – Volume is low, because the fluid will remain in the vascular
• ECF volume imbalances space
- Hypovolemia-> ECV deficit • Hypotonic - lower osmolality than blood. When a
- Hypervolemia-> ECV excess hypotonic solu<on is infused, water moves by
• Osmolality (fluid concentraBon) imbalances osmosis from the vascular system into the cells
- Hypernatremia (Na+- major ion in the ECF) à “water • Hypertonic - contains a higher concentra<on of
deficitӈ hyperosmolality->hypertonic solutes than does blood. When a hypertonic
- Hyponatremia à “water excess”à hypoosmolality- solu<on is given to a pa<ent, water moves by
>hypotonic osmosis from the cells into the ECF
• DehydraBon (â Volume & Electrolyte changes-
hyperosmolarity) = ECV deficit • Diffusion
• OverhydraBon – ( ↑ Volume or Electrolyte - A passive process by which molecules of a solute
changes-hypoosmolarity= ECV excess move through a cell membrane from an area of
higher concentra<on to an area of lower
concentra<on. Movement occurs un<l the
concentra<ons are equivalent on both sides of the
membrane. (e.g. teabag-water)

• FiltraBon
- the movement of both water and smaller par<cles
from an area of high pressure to one of low
pressure.
- Hydrosta<c pressure is the force created by fluid
within a closed system; it is responsible for normal
circula<on of blood->blood flows from the high-
The principle of Fluids and Electrolytes Movement pressure arterial system to the lower-pressure
• Osmosis capillaries and veins.
• Diffusion
• Filtra<on AcBve Transport
• Ac<ve transport • occurs when molecules (e.g., electrolytes) move
across cell membranes against a concentra<on
Passive Transport gradient (from an area of low concentra<on to an
• Osmosis area of high concentra<on). Ac<ve transport
- Involves movement of water (or other pure solute) requires energy expenditure
across a membrane from an area of a less
concentrated solu<on to an area of more WHAT FROM AREA
PROCESS TO AREA OF
concentrated solu<on. Water moves across the MOVES OF
membrane to dilute the higher concentra<on of
Molecules High Low
solutes. (e.g strawberry- sugar/Cabbage-salt) Diffusion
(solute) concentra<on concentra<on
Ac<ve Molecules Low High
Osmolality of a fluid is a measure of the number of transport (solute) concentra<on concentra<on
par<cles (solute) per Kg of water. Fluid that contains a
Low High
large number of dissolved par<cles is more Osmosis Water
concentra<on concentra<on
concentrated than the same amount of fluid that
Water and
contains only a few par<cles. (High: dehydra<on) Filtra<on small High pressure Low pressure
par<cles
• Isotonic - same osmolality as blood; thus, no
osmosis (movement of water) will occur. Isotonic
fluids are oqen given by IV infusion if blood volume


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, RegulaBon of Fluids - Hypervolemia -> ↑ fluid pressures -> less ADH is
Fluid Intake released -> the kidneys eliminate more fluid.
• Primarily through drinking waters - ADH is also produced in response to a rise in serum
• Ins<tute of Medicine (IOM) recommenda<on osmolality, fever, pain, stress (e.g. surgery), and
- 2,700 mL/day women some opioids.
- 3,500 mL/day men
• 20% from food/metabolism of food; 80% water • Renin-angiotensin system
• Fluid intake regulated by thirst (the conscious desire - When extracellular (i.e., intravascular) fluid volume
for water-an important fluid intake regulator) is decreased, receptors in the glomeruli respond to
- Change in plasma osmolality the decreased perfusion of the kidneys by releasing
- Hypothalamus (thirst control center) renin.
- Renin: enzyme responsible for the chain of
Fluid Output reac<ons that converts angiotensinogen to
• Sensible fluid loss - measurable and/or perceived angiotensin II.
(e.g., urine, diarrhea, ostomy, and gastric drainage) - Angiotensin II: acts on the nephrons to retain
!Urine: 1,500 mL/day; at least 30 to 50 mL/hour. sodium and water and directs the adrenal cortex to
- increases as fluid intake increases, and it decreases release aldosterone.
to compensate for other fluid losses (e.g., vomi<ng
and excessive perspira<on). • Aldosterone
• Insensible fluid loss – not measurable and/or not - When aldosterone is released via the renin-
perceived - about 900 mL per day. angiotensin system, it s<mulates the distal tubules
!Skin: Perspira<on - about 600 mL/day; fever, of the kidneys to reabsorb sodium and excrete
exercise potassium. Sodium reabsorp<on results in passive
!Lungs: Exhala<on - about 300 mL/day reabsorp<on of water, thereby increasing plasma
!Feces: 100 to 200 mL/day volume and improving kidney perfusion. When fluid
! Some disease processes increase metabolic ac<vity excess is present, renin is not released, and this
and heat produc<on, leading to increased fluid loss. process stops.

SBmulants that cause THIRST: • Other Hormones:
- Thyroid hormone affects fluid volume by
influencing cardiac output. An increase causes an
increase in cardiac output, thereby increasing
glomerular filtra<on rate and urine output. A
decrease has the opposite effect
- PepBde hormones promote diuresis, natriuresis
(sodium excre<on), vasodila<on of the system,
reduc<on of circula<on of aldosterone
- Brain natriureBc pepBde promote diuresis,
natriuresis, vasodila<on of the systemic and
pulmonary vasculature, and reduc<on of circula<ng
Hormonal RegulaBon levels of endothelin and aldosterone->detect
The kidneys are the principal regulator of fluid and cardiac, renal, and pulmonary disease
electrolyte balance.
• AnBdiureBc hormone (ADH) - Pressure sensors in Primary Organs of Homeostasis
the vascular system -> s<mulate or inhibit the • Kidneys normally filter 170 L of plasma and excrete
release of ADH-> 1.5 L of urine.
- Hypovolemia-> ↓ fluid pressures within the system • Cardiovascular system pumps and carries nutrients
-> releasing ADH from the pituitary gland-> the and water in body.
kidneys reabsorb more fluid. • Lungs regulate oxygen and carbon dioxide levels of
the blood.

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