Module 4 - Fluid Imbalances

ADH (Antidiuretic Hormone)

A hormone produced in the hypothalamus and released by the posterior pituitary that regulates water reabsorption by the kidneys

SIADH Pathophysiology

Excessive release of ADH causes the kidneys to reabsorb too much water, leading to fluid overload, weight gain, and dilutional hyponatremia

Diabetes Insipidus (DI) Manifestations

Key signs include polyuria (excessive urination), polydipsia (extreme thirst), and a very low urine specific gravity

Edema

An excessive accumulation of fluid specifically within the interstitial compartment, which results in the swelling or enlargement of tissues

Causes of Edema

Major causes include increased capillary hydrostatic pressure, loss of plasma proteins (like albumin), and increased capillary permeability

Dehydration

A state of insufficient body fluid resulting from inadequate intake, excessive loss (such as through sweating or vomiting), or both

Manifestations of Dehydration

Common clinical signs include dry mucous membranes, decreased skin turgor, tachycardia, and hypotension

Third-Spacing

A situation where fluid shifts out of the blood and into a body cavity or tissue where it is trapped and no longer available as functional circulating fluid

Lab Trends in Dehydration

Typical findings include an increased hematocrit, increased serum sodium (hypernatremia), and high urine specific gravity

Lab Trends in Edema

Expected findings include a decreased hematocrit, decreased serum sodium (hyponatremia), and low serum albumin

Aldosterone

A hormone produced by the adrenal cortex that promotes the reabsorption of sodium and water in the kidney tubules to maintain blood volume

Atrial Natriuretic Peptide (ANP)

A hormone released by the heart when pressure is high

Pitting Edema

A type of swelling where applying firm pressure with a finger leaves a temporary indentation in the skin

Hydrostatic Pressure

The "pushing" force exerted by a fluid against a surface, which forces fluid out of the capillaries at the arteriolar end

Osmotic/Oncotic Pressure

The "pulling" force that draws water toward areas with higher concentrations of proteins or electrolytes, such as pulling fluid back into the venous end of a capillary

Ascites

A condition resulting from fluid accumulation within the abdominal (peritoneal) cavity, often associated with heart or liver failure

Hemoconcentration

An increase in the proportion of red blood cells in the blood that occurs when the liquid plasma is lost through dehydrationAldosterone

Anion

An ion that carries a negative electrical charge

Antidiuretic hormone (ADH)

A hormone that regulates the amount of water the kidneys reabsorb

Ascites

A condition where excess fluid accumulates within the abdominal cavity, causing swelling

Atrial natriuretic peptide (ANP)

A hormone released by the heart when pressure in its chambers is too high to prompt the kidneys to excrete sodium and lower blood volume

Baroreceptor

Specialized sensors in the walls of major arteries that detect blood pressure changes and signal the brain to adjust heart rate

Capillary permeability

The degree to which the walls of the smallest blood vessels allow water, proteins, and other substances to pass into surrounding tissues

Cation

An ion that carries a positive electrical charge

Dehydration

A state of insufficient body fluid caused by losing more water than is taken in

Diabetes insipidus

A disorder caused by a lack of ADH that produces massive amounts of dilute urine

Diffusion

The natural movement of solutes from an area of high concentration to an area of low concentration

Diuretic

A medication or substance that increases urine production to help the body eliminate excess fluid and sodium

Edema

Swelling due to excessive fluid

Extracellular fluid

Fluid in the body located outside of the cells

Filtration

The movement of water and solutes from an area of higher pressure to an area of lower pressure

Hemoconcentration

An increase in the proportion of red blood cells because plasma has been lost through dehydration

Hemodilution

A decrease in the concentration of cells in the blood due to an excess of water in circulation

Hydrostatic pressure

The pushing force exerted by a fluid against a surface

Hypernatremia

A condition where the sodium level in the blood is abnormally high due to water loss

Hypertonic/hyperosmolar

A state where fluid has a higher concentration of solutes than normal, which pulls water out of cells

Hyponatremia

A condition where the sodium level in the blood is abnormally low due to sodium dilution by excessive water

Hypovolemia

A decreased volume of circulating blood which can lead to low blood pressure

Osmosis

The movement of water across a membrane from an area with fewer solutes to an area with a higher solute concentration

Osmoreceptor

Specialized cells in the brain's hypothalamus that monitor the concentration of body fluids

Osmotic/oncotic pressure

A pulling force that draws water toward areas with high concentrations of protein or electrolytes

Pitting edema

Swelling where firm pressure leaves a temporary indentation in the skin

Third-spacing

A situation where fluid shifts out of the blood and into a body cavity where it is no longer available as circulating fluid

Three causes of dehydration

Vomiting/diarrhea, excessive sweating, and inadequate water intake

Three causes of edema

Increased capillary hydrostatic pressure, loss of plasma proteins, and increased capillary permeability

Dehydration lab trends

Increased hematocrit, increased serum sodium, and high urine specific gravity

Edema lab trends

Decreased hematocrit, decreased serum sodium, low serum albumin, and low urine specific gravity

Third-spacing lab trends

Increased hematocrit, increased BUN, and decreased urine output

Renin production and stimulus

Produced by the kidneys and stimulated by decreased renal blood flow

Angiotensin II effects if prolonged

Can lead to myocardial hypertrophy and heart failure

Cortisol production and stimulus

Produced by the adrenal cortex and stimulated by stress

Case study: Clinical signs of dehydration

Dry mouth, poor skin turgor, lightheadedness, hypotension, and tachycardia

Case study: Clinical signs of third-spacing

Hypotension, confusion, and abdominal distention

SIADH Pathophysiology

A condition where too much ADH is released, causing the kidneys to retain excessive water, which dilutes blood sodium and leads to fluid buildup

Diabetes Insipidus (DI) Pathophysiology

A condition where there is insufficient ADH or the kidneys fail to respond to it, resulting in the inability to retain water and causing excessive urine output

Common causes of SIADH

These include brain injury or infection, certain cancers like lung cancer, and specific medications like SSRIs or chemotherapy

Common causes of Diabetes Insipidus

These include damage to the pituitary gland or hypothalamus, certain medications like lithium, or kidney resistance to ADH

Manifestations of Diabetes Insipidus

Key signs include polyuria (excessive urination), polydipsia (excessive thirst), dry skin, and a low urine specific gravity

Edema

The accumulation of excess fluid in the interstitial compartment, which causes swelling or enlargement of tissue

Dehydration definition

Specifically refers to a water deficiency that often leads to increased serum sodium levels and osmolarity

Fluid Volume Deficit (FVD)

A broader term than dehydration that includes the loss of both water and electrolytes across all fluid compartments

Clinical manifestations of dehydration

Common signs include decreased blood pressure, increased heart rate, dry mucous membranes, and decreased skin turgor

Third-Spacing

A situation where fluid shifts from the blood into a "potential space" (like the peritoneum or lungs), meaning the total body fluid volume stays the same but is not available as circulating fluid

Common causes of third-spacing

These include inflammation, trauma, severe burns, infection/sepsis, and cirrhosis

Lab findings in third-spacing

Expected results include increased hematocrit and BUN (Blood Urea Nitrogen), along with decreased urine output

Signs of hypovolemia due to third-spacing

Clinical indicators include low blood pressure, increased heart rate, cool extremities, and mental status changes

Ascites

The accumulation of fluid in the peritoneal cavity, which is a common form of third-spacing