Ch. 7 - Fluid and Electrolyte Imbalances

Pathophysiology Exam 2

What percentage of an adult’s body weight is water?

Approximately 60% (varies on age, sex, and body composition)

What are the two major fluid compartments in the body?

Intracellular fluid (ICF) and extracellular fluid (ECF)

Where is intracellular fluid (ICF) located?

Inside the body’s cells

Approximately what percentage of total body water is intracellular?

About two thirds

Where is extracellular fluid located?

Outside the body’s cells

What are the two main components of extracellular fluid?

Interstitial fluid and intravascular (plasm) fluid

What is interstitial fluid?The

fluid that surrounds and bathes the body’s cells

What is intravascular fluid?

The plasma portion of blood that remains inside blood vessels

What is the primary electrolyte in the extracellular fluid?

Sodium (Na+)

What is the primary electrolyte in the intracellular fluid?

Potassium (K+)

Why is sodium the major extracellular electrolyte?

It is the primary determinant of extracellular fluid volume and helps regulate water balance

Why is potassium the major intracellular electrolyte?

It is essential for normal nerve conduction, muscle contraction, and cardiac function

What is osmosis?

The movement of water across a semipermeable membrane from an area of lower solute to an area of higher solute concentration

Why does water move during osmosis?

To equalize solute concentrations on both sides of the membrane

What is diffusion?

The movement of solute particles from an area of higher concentration to an area of lower concentration

What is filtration?

The movement of water and small solutes across a membrane due to pressure differences

What is active transport?

The movement of substances across a membrane against their concentration gradient using energy (ATP)

What is the sodium-potassium pump?

An ATP-dependent pump that moves 3 sodium ions out of the cell and 2 potassium ions into the cell

Why is the sodium-potassium pump important?

It maintains normal intracellular and extracellular electrolyte concentrations and is essential for nerve impulses and muscle contraction

What is osmolality?

A measure of the concentration of dissolved particles in a solution

What happens to water when plasma osmolality increases?

Water moves out of cells and into the extracellular space

What happens to water when plasma osmolality decreases?

Water moves into cells

What is hydrostatic pressure?

The pressure exerted by fluid that pushes water out of blood vessels into the surrounding tissues

What is oncotic (colloid osmotic) pressure?

The pulling force created primarily by plasma proteins, especially albumin, that draws water into blood vessels

Which plasma protein contributes most to oncotic pressure?

Albumin

What is the relationship between hydrostatic and oncotic pressure?

Hydrostatic pressure pushes fluid out of capillaries, while oncotic pressure pulls fluid back into capillaries

What happens if hydrostatic pressure becomes too high?

Excess fluid moves into the tissues, causing edema

What happens if oncotic pressure becomes too low?

Fluid remains in the tissues because there is not enough protein to pull it back into the bloodstream, causing edema

What conditions can decrease oncotic pressure?

Liver disease, kidney disease (protein loss), malnutrition, and severe burns

What is edema?

Excess accumulation of fluid in the interstitial tissues

What is hyponatremia?

A serum sodium level less than 135 mEq/L

What is hypernatremia?

A serum sodium level greater than 145 mEq/L

What is sodium’s primary role in the body?

Sodium is the major extracellular electrolyte that regulates water balance, extracellular fluid volume, nerve impulse transmission, and muscle function

Why is sodium important for fluid balance?W

äter follows sodium, so changes in sodium concentration affect where water moves in the body

What happens to water during hyponatremia?

Water moves into cells by osmosis, causing cellular swelling

Which cells are most affected by hyponatremia?

Brain cells, because swelling inside the rigid skull can rapidly increase intracranial pressure

Why is hyponatremia especially dangerous?

Cerebral edema can lead to confusion, seizures, coma, and brain herniation in severe cases

What are common causes of hyponatremia?

Diuretics, vomiting, diarrhea, heart failure, kidney disease, SIADH, excessive water intake, adrenal insufficiency, and severe burns

What are common signs and symptoms of mild hyponatremia?

Nausea headache, fatigue, muscle cramps, and weakness

What are common signs and symptoms of severe hyponatremia?

Confusion, decreased level of consciousness, seizures, coma, and respiratory arrest

Why does hyponatremia cause confusion?

Brain swelling interferes with normal neuronal function

How is mild hyponatremia treated?

Treat the underlying cause and correct sodium gradually, often with fluid restriction id appropriate (such as in SIADH)

How is severe symptomatic hyponatremia treated?

Carefully monitored hypertonic saline (3% sodium chloride) may be used to raise sodium safely

Why must hyponatremia be corrected slowly?

Correcting sodium too rapidly can cause osmotic demyelination syndrome (ODS, resulting in severe neurological injury

What happens to water during hypernatremia?

Water moves out of cells into the extracellular fluid, causing cellular dehydration

Why does hypernatramia cause neurological symptoms?

Brain cells shrink as water leaves them, impairing normal brain function

What are common causes of hypernatremia?

Dehydration, diabetes insipidus, inadequate water intake, fever, excessive sweating, severe burns, and excessive sodium intake

What are common signs and symptoms of hypernatremia?

Intense thirst, dry mucous membranes, irritability, weakness, confusion, muscle twitching, seizures, and coma

Why is thirst a hallmark symptoms of hypernatremia?

Increased serum osmolality stimulates the hypothalamic thirst center

How is hypernatremia treated?

Gradual replacement of free water and treatment of the underlying cause

Why must hypernatremia also be corrected slowly?

Rapid correction can cause cerebral edema as water moves back into brain cells too quickly

What neurological symptoms can occur in both hyponatremia and hypernatremia?

Confusion, seizures, decreased level of consciousness, and coma

What is the major difference between brain cells in hyponatremia and hypernatremia?

In hyponatremia, brain cells swell; in hyponatremia, brain cells shrink

Which condition causes cellular swelling?

Hyponatremia

Which condition causes cellular dehydration?

Hypernatreamia

Which endocrine disorder commonly causes hypernatremia?

Diabetes insipidus

Which endocrine disorder commonly causes hyponatremia?

SIADH

Why does SIADH cause hyponatremia?

Excess ADH causes water retention which dilutes the sodium concentration in the blood

Why does diabetes insipid commonly cause hypernatremia?

Excessive water loss concentrates sodium in the blood stream

What is the key thing to remember from ch. 7?

Sodium controls water movement, low sodium causes water to move into cells (swelling), while high sodium causes water to move out of cells (shrinkage)

What is fluid volume deficit (hypovolemia)?

A decrease in the amount of fluid within the extracellular compartment, especially the intravascular space

What are common causes of fluid volume deficit?

Vomiting, diarrhea, hemorrhage, burns, excessive sweating, diuretics, dehydration, and diabetes insipidus

What are the signs and symptoms of fluid volume deficit?

Hypotension, tachycardia, dry mucous membranes, poor skin turgor, decreased urine output, dizziness, thirst, and weight loss

Why does hypovolemia cause tachycardia?

The heart beats faster to maintain cardiac output when blood volume is decreased

Why does hypovolemia cause hypotension?

Reduced circulating blood volume decreased venous return, stroke volume, and cardiac output, lowering blood pressure

Why is urine output decreased in hypovolemia?

The kidneys conserve water by decreasing urine production to help restore blood volume

What laboratory values are commonly seen in dehydration?

Increased hematocrit, increased blood urea nitrogen (BUN), increased serum osmolality, and sometimes hypernatremia, depending on the cause

How is hypovolemia treated?

Replace fluids with oral hydration if appropriate or intravenous fluids, and treat the underlying cause

What is fluid volume overload (hypervolemia)?

An excess of fluid in the extracellular compartment

What are common causes of fluid volume overload?

Heart failure, kidney failure, liver disease, excessive IV fluids, and excess sodium intake

What are the signs and symptoms of fluid volume overload?

Edema, weight gain, hypertension, jugular venous distention (JVD), pulmonary crackles, dyspnea, and bounding pulses

Why does fluid overload cause edema?

Increased hydrostatic pressure pushes excess fluid from the capillaries into the tissues

Why does fluid overload cause pulmonary edema?

Excess fluid leaks from pulmonary capillaries into the lung tissue and alveoli, impairing gas exchange

What are the signs of pulmonary edema?

Dypnea, crackles, orthopnea, hypoxemia, and pink frothy sputum in severe cases

How is fluid volume overload treated?

Treat the underlying cause, restrict sodium and fluids when indicated, and administer diuretics if appropriate

What are the three categories of IV fluids based on tonicity?

Isotonic, hypotonic, and hypertonic solutions

What is an isotonic IV solution?

A solution with approximately the same osmolality as plasma, causing little or no net movement of water into or out of cells

What is a common isotonic IV solution?

0.9% normal saline (NS) or lactated ringers (LR)

When are isotonic fluids commonly used?

To expand intravascular volume in patients with hypovolemia, dehydration, or blood loss

What is a hypotonic IV solution?

A solution with a lower osmolality than plasma that causes water to move into cells

What is a common hypotonic IV solution?

0.45% normal saline

When are hypotonic fluids used?

To treat cellular dehydration, such as some cases of hypernatremia, when appropriate

Why must hypotonic fluids be used cautiously?

They can cause excessive cellular swelling and worsen cerebral edema

What is a hypertonic IV solution?

A solution with a higher osmolality than plasma that pulls water out of cells into the blood stream

What are examples of hypertonic IV solutions?

3% normal saline, 5% normal saline, and D10W (10% dextrose in water)

When are hypertonic solutions commonly used?

For severe symptomatic hyponatremia or certain situations requiring rapid expansion of intravascular volume under close monitoring

Why can hypertonic solutions be dangerous?

They can cause fluid overload, pulmonary edema, and rapid shifts in sodium and water if not carefully monitored

Which IV fluid is usually the first choice for treating hypovolemic shock?

An isotonic crystalloid such as 0.9% normal saline or lactated ringers unless there is a specific reason to choose another fluid

Why are isotonic fluids preferred fro initial blood volume replacement?

They remain primarily in the extracellular space, helping restore circulating blood volume without causing major fluid shifts into or out of cells

What is the key concept of IV fluid tonicity?

Isotonic = no major fluid shift

Hypotonic = water moves into cells

Hypertonic = water moves out of cells

What is the primary function of the Renin-Angiotensin-Aldosterone System (RAAS)?

To maintain blood pressure, blood volume, and sodium imbalance

What is the primary function of the Renin-Angiotensin-Aldosterone System (RAAS)?

Decreased blood pressure, decreased blood volume, decreased kidney perfusion, or decreased sodium delivery to the kidneys

Which organ releases renin?

The kidneys (juxtaglomerular cells)

What stimulates the kidneys to release renin?

Low blood pressure, low blood volume, decreased renal blood flow, or sympathetic nervous system activation

What does renin do?

It converts angiotensinogen (made by the liver) into angiotensin I

Where is angiotensinogen produced?

The liver

Which enzyme converts angiotensin I into angiotensin II?

Angiotensin-converting enzyme (ACE, found mainly in the lungs and vascular endothelium

What is the major active hormone of the RAAS?

Angiotensin II

What are the major actions of angiotensin II?

Vasoconstriction, stimulation of aldosterone release, stimulation of ADH release, and stimulation of thirst

Why does angiotensin II increase blood pressure?

It causes vasoconstriction and increases blood volume through aldosterone and ADH