Fluid Volume Balance & IV Fluids

Vocabulary-style flashcards covering fluid compartments, mechanisms of fluid movement, hormonal regulation, fluid volume deficits and excesses, IV solutions, and key clinical concepts.

Homeostasis

A state of equilibrium maintained by adaptive responses involving fluids, electrolytes, and acid/base balance.

Intracellular Fluid (ICF)

Fluid located inside the cells, making up approximately $\frac{2}{3}$ of total body fluid and primarily residing in skeletal muscle.

Extracellular Fluid (ECF)

Fluid found outside the cells, constituting about $\frac{1}{3}$ of body fluid, which includes intravascular, interstitial, and transcellular compartments.

Intravascular Fluid

The liquid component of extracellular fluid located within blood vessels, primarily consisting of blood plasma.

Interstitial Fluid

The portion of extracellular fluid occupying the spaces surrounding individual tissue cells.

Transcellular Fluid

Specialized extracellular fluid contained within specific epithelial-lined spaces, such as cerebrospinal, pericardial, synovial, and intraocular fluids.

Osmosis

The passive movement of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Diffusion

The passive movement of solutes from an area of higher solute concentration to an area of lower solute concentration across a permeable membrane.

Active Transport

The energy-requiring process that moves solutes and water across a cell membrane against a concentration gradient, such as the $\text{Na}^+/\text{K}^+$ pump.

Hydrostatic Pressure

The physical force exerted by fluid pushing outward against capillary walls to drive water and solutes across membranes.

Oncotic Pressure

The osmotic force exerted by plasma proteins (such as albumin) that holds water inside the vascular compartment.

Osmolality

A measurement of serum fluid concentration reflecting hydration status, with normal values ranging from $280 - 295\,\text{mOsm/kg}$.

Renin-Angiotensin-Aldosterone System (RAAS)

A multi-organ hormonal feedback mechanism triggered by low blood pressure or low kidney perfusion that causes sodium and water retention along with vasoconstriction to elevate blood pressure.

Antidiuretic Hormone (ADH)

A pituitary hormone released in response to high plasma osmolality or low blood volume that increases renal reabsorption of water.

Atrial Natriuretic Peptide (ANP)

A hormone secreted by heart atrial cells in response to wall stretching that promotes renal sodium and water excretion.

Brain Natriuretic Peptide (BNP)

A peptide released by cardiac ventricular cells due to increased stretch and fluid overload, used clinically as a diagnostic marker for heart failure.

Hypovolemia

An isotonic fluid volume deficit characterized by loss of water and electrolytes from the intravascular space.

Oliguria

A pathologically diminished production of urine, typically defined as less than $0.5\,\text{mL/kg/hr}$ or approximately less than $30\,\text{mL/hr}$.

Isotonic Fluids

Intravenous fluids with an osmolality equal to body serum (e.g., $0.9\%$ Normal Saline, Lactated Ringer's) that expand intravascular volume without shifting water into or out of cells.

Hypertonic Fluids

Intravenous fluids with a higher osmolality than serum (e.g., $3\%$ NaCl, $5\%$ NaCl) that draw fluid out of cells into the vascular space, causing cells to shrink.

Hypotonic Fluids

Intravenous fluids with a lower osmolality than serum (e.g., $0.45\%$ Normal Saline) that cause fluid to move out of blood vessels into body cells, causing them to swell.

Plasma Volume Expanders (PVEs)

Colloid solutions or blood products that remain in the intravascular space and raise oncotic pressure to pull and retain fluid within blood vessels.

Hypervolemia

Fluid volume excess caused by abnormal retention of water and sodium in extracellular compartments.

Jugular Venous Distension (JVD)

Visible bulging of the jugular veins in the neck caused by elevated central venous pressure and intravascular volume excess.

Pitting Edema

Accumulation of excess fluid in interstitial tissues that leaves a persistent depression or indentation when pressure is applied.

Third Spacing

The abnormal shifting and trapping of fluid into body compartments or transcellular spaces where it is functionally unavailable for metabolic processes or exchange.

Euvolemic

The physiological state of possessing a normal, healthy volume of body fluids.