Fluid balance

What percentage of the human body is fluid?

60%

What are two major fluid compartments?

Intracellular fluid and extracellular fluid

What portion of body water is intracellular

2/3

Where is intracellular fluid located

Inside the cells (2/3 of water in skeletal muscle is intracellular)

What portion of body water is extracellular

1/3

The 3 extracellular fluid compartments

• intravascular

• interstitial

• transcellular

How much fluid is in the intravascular compartment

6 Liters

What makes up the 6L of intravascular fluid

• 3L plasma

• 3L erythrocytes, leukocytes, and thrombocytes

What is interstitial fluid

Fluid that surrounds the cells

How much fluid is in the transcellular compartment

About 1 L

Examples of transcellular fluid

• CSF

• pericardial fluid

• synovial fluid

• pleural fluid

• digestive secretions

For major functions of water

• solvent

• transport

• thermoregulation

• lubricant

What four processes move fluid between compartments

• Diffusion

• Active transport

• Filtration

• Osmosis

Diffusion

Movements of particle from higher concentration —> lower concentration

Does diffusion require energy

No

What is active transport

Movement of particles from lower concentration —> higher concentration (against the concentration gradient)

Does active transport require energy

Yes- ATP

Filtration

Movement of water across a semipermeable membrane due to pressure differences rather than concentration differences

Osmosis

Movement of water across a semipermeable membrane from an area of lower solute concentration —> higher solute concentration

Oncotic pressure

Pressure exerted by plasma proteins (mostly albumin)

Fluid balance is maintained via…

Input and output

What regulates fluid intake

• Thirst

• Dietary intake

• Tube feeds

• Parenteral infusions

What organs regulates fluid output

• Kidneys

• Skin

• GI tract

• Lungs

How much fluid do the kidneys normally excrete per day

1-2 L/day (1.5 avg)

Insensible fluid losses

Fluid losses that occur through the skin, lungs and stool

What hormones help the kidneys maintain fluid balance

• Aldosterone

• ADH (antidiuretic hormone)

• ANP (atrial natriuretic peptide)

What does antidiuretic hormone do

Promotes water retention

Where is antidiuretic hormone made

hypothalamus; stored in pituitary gland

What does aldosterone cause

• Na+ and H2O retention

• K+ excretion

What regulates fluid balance through pressure sensing

Baroreceptors & mechanical sensor proteins

What hormonal system regulates fluid balance and blood pressure

Renin-angiotensin-aldosterone system (RAAS)

What triggers the Renin-angiotensin-aldosterone system (RAAS)

• Drop in BP

• Low blood volume

• Low Na+ levels

What natriuretic peptides are involved in fluid regulation?

• Atrial natriuretic peptide (ANP)

• Brain natriuretic peptide (BNP)

What are natriuretic peptides

Hormones released by your heart / blood vessels when the heart muscle is stretched under stress

Dehydration

Loss of body fluid

Causes of hypovolemia

• GI loss (N/V/D, GI suctioning)

• Sweating

• Hemorrhaging

• Decreased intake

Risk factors for hypovolemia

• Hyperventilation

• Third spacing

• Adrenal insufficiency

• DKA/DI

S/s of hypovolemia

• Hypotension

• Tachycardia

• Tachypnea

• Cool/clammy skin

• Oliguria

• Flattened jugular vein

• Muscle cramps

Common lab findings with hypovolemia

• increased blood and urine osmolality

• increased urine specific gravity

• increased Hgb/Hct

• increased BUN/Creatinine ratio

• Metabolic acidosis

How is hypovolemia treated

Fluids (PO or IV), specifically isotonic solutions (normal saline, lactated ringers)

Causes / risk factors of hypervolemia

• Poor fluid excretion

• Heart failure

• Kidney failure

• Cirrhosis

• Burns

• Corticosteroids

S/s of hypervolemia

• Edema

• Crackles

• JVD

• Tachycardia

• Hypertension

• Dyspnea

• Bounding pulse

Common lab findings with hypervolemia

• decreased blood and urine osmolality

• decreased urine specific gravity

• decreased Hct/Hgb

How is hypervolemia treated

• Treat the initial cause

• Diuretics

• Fluid restriction

What position is used for orthopnea with fluid overload

Semi-fowlers

What amount of weight gain should be reported in a hypervolemic patient

1-2lbs in 24 hr OR 3lbs in 1 week

Hypotonic solution

Solution that moves water in the cells and hydrates them (lower concentration of dissolved particles than the inside of a cell)

Hypertonic solution

Solution that pulls fluid out of cells and into the bloodstream (higher concentration of dissolved particles than the inside of a cell)

Isotonic solution

Solution with an equal concentration of dissolved particles compared to the inside of a cell, so it “stays in the vessel”

_________ solution infusions can be used to move water from the ECF into the ICF

Hypotonic

_______ solution can be infused into the bloodstream to pull water from the ICF into the ECF (causes dehydration of cells)

Hypertonic

Examples of isotonic IV solutions

• Lactated Ringer’s

• D5W

• 0.9% NaCl

Examples of hypertonic IV solutions

• 3% NaCl

• 5% NaCl

• D10W

Examples of hypotonic IV solutions

• 0.45% NaCl

• 0.33% NaCl

Where does water move with a hypotonic solution

into the cells; ECF —> ICF

What do hypotonic solutions do to cells?

Water rushes into the cells, causing them to swell (via osmosis)

What happens to plasma volume with isotonic solutions?

Plasma volume increases because isotonic solutions stay in the extracellular space

Common uses of hypotonic solutions

• Fluid loss post-op

• Hypernatremia

Common uses of isotonic solutions

• Dehydration

• Blood loss

• Hypotension

• Hypovolemic shock

What do colloid solutions do

Pulls fluid into the intravascular space and increases blood volume when crystalloids aren’t enough

When are colloids used

• Low albumin

• Severe edema

• Major fluid shifts

• Severe hypovolemic shock

examples of colloid solutions

• albumin

• FFP

• PRBCs