Ch. 12 Fluid Volume and Electrolytes

Total Body Water (TBW)

60% of body weight in adults

Intracellular Fluid

Fluid contained within cells.

Extracellular Fluid (ECF)

Fluid outside the cells, including interstitial fluid, transcellular fluids, and intravascular fluid.

Interstitial fluid

Fluid found in the spaces between cells.

Transcellular fluids

Fluids that are contained within specialized compartments.

Intravascular fluid

Fluid found within blood vessels.

electrolytes

chemicals or nutrients in the body's fluid compartment ands have important functions (impact fluid volume, regulate cardiac contractions, and provide stimulation to skeletal muscle)

Fluid Output

Loss of fluids through kidneys, lungs, feces, sweat, and skin.

Fluid Intake

The consumption of fluids, not specified in the notes.

Two Populations at Risk for Dehydration

Pediatrics and aging (older adults).

Pediatrics

TBW 75-80% of body weight at birth, susceptible to significant changes in body fluids.

Aging

Decreases % of TBW, decreases free fat, and decreased muscle mass.

Homeostasis

Anions/cations balanced, fluid compartments in osmotic equilibrium, fluid/particle movement.

Osmosis

Movement of water across a semipermeable membrane.

Diffusion

Movement of particles from an area of higher concentration to an area of lower concentration.

Hydrostatic pressure

Pressure exerted by a fluid at equilibrium due to the force of gravity.

Active transport

Energy-dependent process of moving substances across a cell membrane.

Osmolality

A measure of the number of particles dissolved in a fluid, typically blood or urine, per kg of solvent.

Edema

Accumulation of fluid within the interstitial spaces.

Causes of Edema

Increase in capillary hydrostatic pressure, decrease in plasma oncotic pressure, increase in capillary permeability, lymph channel obstruction.

What is the primary cation in extracellular fluid (ECF)?

Sodium (Na+)

What is the normal range for sodium levels in extracellular fluid (ECF)?

136 to 145 mEq/L

What role does sodium play in nerve impulse conduction?

It regulates osmotic balances.

How does sodium affect water balance in the body?

Where sodium goes, water follows.

What is the effect of sodium on extracellular fluid volume?

It maintains ECF volume via effects on osmotic pressure.

What happens to fluid volume and other electrolyte levels when sodium levels change?

They also change; high sodium levels in the ECF pull water out of the cell.

How does sodium move between vascular and interstitial fluid?

By active transport through the sodium-potassium pump.

What is the role of sodium in maintaining electrical neutrality in the body?

Levels must equal anions (negative charge) to maintain an electrically neutral state.

What percentage of ECF solute is sodium needed for muscle contraction and nerve transmission?

About 90%

What is the impact of sodium on ECF osmolarity?

It determines where water moves.

What is the primary role of chloride (Cl-) in the body?

major anion. Regulates osmotic balance and plays a role in acid-base balance.

What is the concentration range of chloride (Cl-) in the body?

98-106 mEq/L

What type of ion is chloride (Cl-)?

Negatively charged anion

What is hypochloremia?

Defined as a low serum chloride level (<98 mmol/liter)

What is hyperchloremia?

Defined as a high serum chloride level (>105 mmol/liter)

What are some causes of hypochloremia?

Alkalosis from vomiting, excess sweating, fluid overload, diarrhea, adrenal insufficiency, diuretics

What are some causes of hyperchloremia?

Hypernatremia, low plasma bicarbonate levels, increased intake of sodium chloride

What may hypochloremia lead to?

Hyponatremia and dehydration

What is the typical treatment for hypochloremia?

Fluid replacement

What may hyperchloremia lead to?

Development of edema and weight gain

What is the treatment for hyperchloremia based on?

The cause of the condition

What ion does chloride (Cl-) tend to follow in the body?

Sodium (Na+)

What is the relationship between high sodium levels and chloride levels?

High sodium levels are accompanied by high chloride levels.

Which ions can switch with chloride ions in circulating blood to assist in maintaining acid-base balance?

Bicarbonate ions (HCO3)

Renin-angiotensin-aldosterone system

Aldosterone controls Na+ concentration; natriuretic peptides increase Na+ and water excretion.

Water Balance Maintained by

ADH (antidiuretic hormone) secretion.

Isotonic Alteration

Fluid loss or gain that does not change the osmotic balance.

Hypertonic Alterations

Increase in osmolality, hypernatremia, H2O deficiency in ECF (dehydration).

Hypotonic Alteration

Decrease in osmolality, hyponatremia, H2O excess in ECF (cerebral edema).

What is hypernatremia?

Hypernatremia is defined as a high blood sodium level (more than 145 mEq/L).

What happens to aldosterone secretion when serum sodium levels are high?

Aldosterone secretion is decreased.

What hormones are stimulated by high serum sodium levels?

ADH (Antidiuretic Hormone) and NP (Natriuretic Peptide) are stimulated.

What is the effect of ADH and NP on the kidneys in hypernatremia?

They cause the kidneys to increase their excretion of sodium and reabsorption of water.

What are some causes of hypernatremia?

Increased sodium intake without equivalent water intake, body water loss faster than sodium loss, decreased ADH secretion, watery diarrhea, and loss of sensation of thirst.

What are some symptoms of increased sodium levels?

Weakness, agitation, thirst, dry mucous membranes, decreased urine output, or edema.

Where does edema typically occur in the body due to increased sodium levels?

Common areas for edema include the lungs, brain, and dependent body areas like the legs and lower back.

What are the most common areas for edema?

The ankle and foot.

What is hyponatremia?

Low blood sodium.

What blood sodium level is considered hyponatremia?

Below 136 mEq/L.

What are some causes of hyponatremia?

Excess ADH, rapid IV fluids without added sodium, vomiting, diarrhea, GI suction, burns, diuretics, low-sodium diets with diuretics, excessive sweating.

How can rapid IV fluids lead to hyponatremia?

5% dextrose in water forms a hypotonic solution and dilutes sodium.

What can excessive water intake due to thirst lead to?

Sodium dilution and hyponatremia.

What conditions can impair water excretion?

Renal failure, heart failure, or cirrhosis.

What happens to total body water and sodium levels in hyponatremia?

Total body water increases while sodium levels do not increase proportionately, leading to hypervolemia.

What symptoms can decreased sodium levels disrupt?

Nerve conduction, leading to fatigue, muscle cramps, nausea, or vomiting.

What can fluid shifts due to hyponatremia cause?

A drop in blood pressure and swelling of brain cells.

What are potential severe consequences of untreated hyponatremia?

Coma and death.

What neurological symptoms can occur due to fluid shifts into brain cells?

Headache, confusion, weakness, seizures.

What effect does low serum sodium have on antidiuretic hormone (ADH) secretion?

Low serum sodium levels decrease the secretion of antidiuretic hormone (ADH).

What effect does low serum sodium have on natriuretic peptide (NP) secretion?

Low serum sodium levels decrease the secretion of natriuretic peptide (NP).

What hormone is triggered by low serum sodium levels?

Aldosterone is triggered by low serum sodium levels.

What is the effect of aldosterone on sodium and water reabsorption?

Aldosterone increases reabsorption of sodium by the kidneys and increases loss of water through the kidneys.

What is the overall result of the hormonal changes due to low serum sodium?

The overall result is an increase in the sodium level.

Cerebral edema

Excess accumulation of fluid in the intracellular/extracellular spaces of the brain.

Fluid Replacement General Considerations

Includes all routes, fluid intake & loss, daily H2O, electrolyte, protein, patient's weight and caloric needs, body surface area, illness, and surgery.

Types of Intravenous Solutions

Crystalloids and colloids.

Crystalloids

Used for short-term maintenance therapy to treat dehydration and electrolyte imbalance.

Colloids

Plasma expanders containing large molecules that increase osmolarity.

Tonicity

The ability of an extracellular solution to make water move into or out of a cell by osmosis.

Isotonic Solution

No net flow of water into or out of the cell, cell volume remains stable.

Hypotonic Solution

Net flow of water into the cell, causing the cell to gain volume.

Hypertonic Solution

Net flow of water out of the cell, causing the cell to lose volume.

Hypertonic Solution

A solution will be hypertonic to a cell if its solute concentration is higher than that inside the cell, and the solutes cannot cross the membrane.

Isotonic IV Fluids Contradictions

Used with caution for cardiac/renal patients; do not administer to patients with increased intracranial pressure (ICP).

Hypotonic IV Fluids Contradictions

Do not administer to ICP (increased cranial pressure) patients.

Hypertonic IV Fluids Contradictions

Use with caution; give slowly via pump, monitor fluid and electrolytes; contraindicated in cardiac, renal, dehydration.

Ins & Outs

If we give you a fluid, we expect a fluid to come out.

IV Fluid Example

A patient is prescribed IV fluids: 1000ml of 5% Dextrose in 0.45% sodium chloride (D51/2NS). This type of fluid is hypertonic.

Electrolyte Values

Na+: 135-145 mEq/L, K+: 3.5 - 5.0 mEq/L, Mg+: 1.5 - 2.5 mEq/L, Ca2+: 8.6 - 10.2 mg/dL, Cl-: 96 - 106 mEq/L, P-: 2.4 - 4.4 mEq/L.

Chloride (Cl-)

Principal anion in Extracellular Fluid (ECF); major contributor of acid-base balance.

Hypochloremia Cues

Cues include tremors and twitching.

Hyperchloremia Cues

Cues include weakness and lethargy.

Sodium (Na+) Purpose

Maintains fluid volume balance, neuromuscular irritability, plasma osmolality, and conduction of nerve impulses.

Hypernatremia

Serum sodium >145 mEq/L; related to Na+ gain or water loss; manifestations include dehydration and dry, sticky mucous membranes.

Hyponatremia

Serum sodium < 135 mEq/L; related to Na+ loss or water gain; manifestations include muscle weakness, headaches, and confusion.

What is the symbol for potassium?

K+

What is the major intracellular cation?

Potassium (K+)

What maintains the concentration of potassium in cells?

Na+/K+ ATPase pump

What is the total potassium content in the body?

4000 mEq

What percentage of potassium is stored in bone?

60%