13 - Concepts of Fluid and Electrolyte Balance & Imbalance

anion

a negatively charged electrolyte

calcium

an important body electrolyte ion having two positive charges (divalent cation)

cation

a positively charged electrolyte

dehydration

a body fluid volume (especially plasma volume) deficit caused by fluid intake or retention below what is needed to meet the body’s daily fluid needs

diffusion

the movement of particles (solute) across a permeable membrane from an area of higher particle concentration to an area of lower particle concentration (down a concentration gradient)

electrolyte

a solute particle that expresses an overall electrical charge (positive or negative)

extracellular fluid (ECF)

the compartment composed of fluids outside of the cells (interstitial fluid and plasma volumes)

facilitated diffusion

the movement across a cell membrane that requires a membrane-altering system

filtration

the movement of fluid through a cell or blood vessel membrane because of hydrostatic pressure (water pressure) differences

fluid and electrolyte balance

the regulation of body fluid volume, osmolarity, and composition; the regulation of electrolytes by the processes of filtration, diffusion, osmosis, and selective excretion

hydrostatic pressure

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

hypercalcemia

a total serum calcium level above 10.5 mg/dL or 2.62 mmol/L

hyperkalemia

a serum potassium level higher than 5.0 mEq/L (mmol/L)

hypermagnesemia

a serum magnesium level above 2.1 mEq/L or 1.05 mmol/L

hypernatremia

a serum sodium level over 145 mEq/L (mmol/L)

hyperosmotic / hypertonic

describes a fluid with an osmolarity greater than 300 mOsm/L

hypervolemia

a fluid overload

hypocalcemia

a total serum calcium (Ca2+) level below 9.0 mg/dL or 2.25 mmol/L

hypokalemia

a serum potassium level below 3.5 mEq/L (mmol/L)

hypomagnesemia

a serum magnesium (Mg2+) level below 1.3 mEq/L or 0.65 mmol/L

hyponatremia

a serum sodium (Na+) level below 136 mEq/L (mmol/L)

hypoosmotic / hypotonic

describes a fluid with an osmolarity less than 270 mOsm/L

hypovolemia

a lower than normal circulating blood volume

insensible water loss

a body water loss that has no mechanisms for control, including losses through the skin, the lungs, GI tract, salivation, and drainage from fistulas and drains

interstitial fluid

the part of extracellular fluid present between cells, also called the third space; it includes blood, lymph, water in the bones and connective tissue, and transcellular fluids

intracellular fluid (ICF)

the compartment composed of fluid inside the cells (cellular fluid)

isosmotic / isotonic

describes a fluid that has the solute (particle) concentration (osmolarity) within the normal range for human body fluids (270 to 300 mOsm/L)

magnesium

an ion that is stored mostly in bones and cartilage

obligatory urine output

the minimum amount of urine output per day needed to excrete toxic waste products (400 to 600 mL)

osmolality

the number of milliosmoles in a kilogram of solution

osmolarity

the number of milliosmoles in a liter of solution

osmosis

the movement of water only through a selectively permeable (semipermeable) membrane to achieve an equilibrium of osmolarity

potassium

the major cation of the intracellular fluid (ICF)

sodium

the major cation (positively charged particle) in the extracellular fluid (ECF)

solute

a particle dissolved in the solvent of body fluids

solvent

a water portion of body fluids