Fluid and Electrolytes Eli

Normal distribution of total body water

ICF

ECF (Blood plasma, interstitial fluid)

Filtration

The movement of fluid through a cell or blood vessel membrane because of hydrostatic pressure differences on both sides of the membrane

Hydrostatic pressure

The pressure exerted by water molecules against the surfaces (membranes or walls) of a confining space

Why does heart failure cause edema or fluid build up in the tissue

The volume of blood in the right side of the heart increases because the right ventricle is too weak to pump blood into lung blood vessels. Since blood (fluid) is backed up in the capillaries and veins, it increases the hydrostatic pressure within the veins and forces fluids into the surrounding tissues

Osmosis

The movement of water only through a selectively permeable membrane to achieve equilibrium

A membrane must have two fluid spaces, and one space must have particles that cannot travel through the membrane

What determines how fast osmosis occurs

The amount of particles in the fluid space which would increase the difference in the hydrostatic pressures

Osmolality vs. osmolarity

Osmolality = number of particles in a Kg of solution

Osmolality = number of particles in a Liter of solution

Isotonic or Isosmotic

When the fluid space is close to 300 mOsm/L. It would be considered normal in pressure

Hypertonic or Hyperosmotic

When the fluids have osmolarity ex greater than 300 mOsm/L

Due to the higher solute concentration, it would pull water from hypotonic or isotonic spaces

Sodium (Na+)

135-145

Elevated: hypernatremia, dehydration, kidney disease, hypercortisolism

Low: Hyponatremia, fluid overload, liver disease, adrenal insufficiency

Potassium (K+)

3.5-5

Elevated: Hyperkalemia, Dehydration, Kidney disease, Acidosis, Adrenal insufficiency, crush injuries

Low: Hypokalemia, fluid overload, diuretics, alkalosis, insulin administration, hyperaldosteronism

Calcium (Ca2+)

9-10.5

Elevated: Hypercalcemia, hyperthyroidism, hyperparathyroidism

Low: Hypocalcemia, Vit. D deficiency, hypothyroidism, hypoparathyroidism, kidney disease, excessive intake of phosphorus

Chloride (Cl-)

98-106

Elevated: hypochloremia, metabolic acidosis, respiratory alkalosis, hypercortisolism

Low: Hypochloremia, fluid overload, vomiting or diarrhea, adrenal insufficiency, diuretics

Magnesium (Mg2+)

1.3-2.1

Elevated: hypermagnesemia, kidney disease, hypothyroidism, adrenal insufficiency

Low: hypomagnesemia, malnutrition, alcoholism, ketoacidosis

What causes the activation of thirst

When osmoreceptors within the brain experience a higher solute concentration in the blood due to dehydration, it causes the fluid in the cells to get pulled out and shrink. This shrinking triggers the response of thirst

electrolytes (ions)

Dissolved substances, that express an electrical charge

Cations (+)

Anions (-)

The difference in electrolytes between semipermeable membranes is what creates membrane excitability and allows nerve impulse transmission

Who is at the greatest risk for electrolyte imbalance

Older pts. (Due to age-related organ changes and they have less total body water)

Pts. With chronic kidney or endocrine disorders

Those taking drugs that alter fluid or electrolyte levels

Age-related changes in fluid balance: skin

> Loss of elasticity And Decreased skin turgor

• Skin becomes an unreliable indicator of fluid status

> Decreased Oil Production

• Dry, easily damaged skin

Age-related changes in fluid balance: Kidneys

> Decreased GFR

• Poor excretion of waste products

> Decreased concentration capacity

• Increase water loss and dehydration

Age-related changes in fluid balance: Neurologic

> reduced thirst reflex

• decreased fluid intake

Age-related changes in fluid balance: Muscular

> Decreased muscle mass

• Decreased total body water which increases risk of dehydration

Age-related changes in fluid balance: Endocrine

> Adrenal atrophy

• Poor Na+ and K+ regulation, increasing risk of hypernatremia and hyperkalemia

Why are women at a higher risk for dehydration

Because they have less total body water due to more fat and less muscle

Measurable versus unmeasurable routes of fluid intake

Measureable: oral fluids, parenteral fluids, enemas, irrigation fluids

Unmeasurable: Solid foods and metabolism

Obligatory Urine Output

400 to 600 mL

The minimum amount of urine output per day needed to excrete toxic waste products

Any less and wastes are retained and can cause lethal electrolyte imbalances , acidosis, and toxic buildup of nitrogen

Insensible water loss

Water loss that no mechanism controls like through the skin, lungs, and intestinal tract

Thyroid crisis, trauma, burns, states of extreme stress, and fever can increase this loss

Which 3 hormones control fluid and electrolyte balance

Aldosterone

Natriuretic peptide

Antidiuretic hormone

Aldosterone

Secreted by the adrenal cortex when sodium levels in ECF get too low

Prevents sodium and water loss

Promotes kidney potassium excretion

Antidiuretic hormone (Vasopressin)

Released from posterior pituitary gland in response to changes in blood osmolarity

tells nephrons to hold onto water only

Natriuretic peptides

Secreted by cells within the lining of the atria within the heart in response to changes in blood pressure

Binds to nephrons and do the opposite of ADH. Stop water from being reabsorbed

What stimulates the secretion of renin and the cascade of the RAAS system?

Low blood pressure

Low blood volume

Low blood sodium

Low blood oxygen

Function of renin

Converts into angiotensin 1 which is then converted into angiotensin 2

What does angiotensin stimulate?

1) constriction of arteries and veins which would increase blood pressure

2) Contricts afferent arterioles in the nephrons which would decrease GFR. This increases water and sodium retention which then increases blood volume

3) Stimulates secretion of aldosterone which would cause sodium and water reabsorption

Role of sodium

Most common cation and maintains ECF osmolarity

Difference in Na+ levels in the ECF and ICF allow for muscle contraction, cardiac contraction, and nerve impulse transmission

Influences water movement

Regulated by ADH, NP, and aldosterone

Role of potassium

Most common cation of the ICF

The major difference in concentration between the ICf and the ECF is critical for excitable tissues to be able to depolarize and generate action potentials

Most of potassium is excreted and removed through the kidneys

Role of Calcium

Either bound (connected to serum proteins like Albumin) or unbound which is an active form and must be kept in a narrow range within the ECF

Important for maintaining bone strength/density, activating enzymes, allowing skeletal and cardiac muscle contraction, controlling nerve impulse transmission, and clotting blood

Regulated by parathyroid hormone and thyrocalcitonin

Role of magnesium

Stored in bones and cartilidge and more common in the ICF

Important for skeletal muscle contraction, carb metabolism, generation of energy stores, vitamin activation, blood coagulation, and cell growth

Vascular dehydration

When water shifts from the plasma in blood to the interstitial space

Why are older adults at more of a risk for dehydration?

• Less total body water

• Decreased thirst reflex

• Difficulty with ADLs needed to obtain fluids

• May take fluid loss meds

Isotonic dehydration

The loss of both water and electrolytes

VS changes due to dehydration

• Increased RR

• Increased HR

• Decreased BP

Neuro and kidney changed with dehydration

• Confusion, lethargy, weakness

• Low-grade fever

• Urine volume and increased concentration

Lab changes due to dehydration

• Increased H/H

• Increased BUN

• Increased osmolarity

• Increased most everything that is common in blood

Pt safety and quality care when dealing with dehydration

• Offer and ensure ingestion of fluids every 2 hours throughout 24 hours

• Teach pt not to withhold fluids due to incontinence

• Infuse IV fluids at a rate consistent with hydration needs

• Monitor for giving too much and leading to fluid overloa

What are the two most important areas to monitor during rehydration

I/O and pulse rate/quality

Is 0.9% saline isotonic or hypotonic?

Isotonic

Hypervolemia

Excessive fluid in the extracellular space

Cardiovascular changes due to fluid overload

• Increased HR

• Bounding Pulse

• Elevated BP

• Decreased Pulse pressure

• Elevated central venous pressure

• Distended neck and hand veins

• WEIGHT GAIN

Respiratory changes due to fluid overload

• Increased RR

• Shallow respirations

• SOB

• Crackles in lungs

Skin changes due to fluid overload

• Pitting edema

• Skin cool and pale to the touch

Neuromuscular changes due to fluid overload

• Altered LOC

• Headache

• Visual disturbances

• Skeletal muscle weakness

• Paresthesia

GI changes due to fluid overload

Increased motility

Enlarged Liver

Assessing pts. fluid overload

• Check every 2 hours for pulmonary edema due to rapid onset

• Contact PCP is overload s/s are worsening

What is the best indicator for fluid deficit or overload

Daily weights