Fluid and Electrolytes Lecture Review

Comprehensive vocabulary flashcards covering fluid and electrolyte balance, compartment distributions, pressures, tonicity, and various IV fluid classifications based on the lecture transcript.

Homeostasis

The maintenance of a constant internal equilibrium in a biologic system.

Solvent

A fluid medium that is part of a solution.

Solutes

Particles that are dissolved or suspended in a solvent within a solution.

Plasma

The liquid component of blood, composed of $92\%$ water, which contains proteins (mainly albumin), glucose, lipoproteins, and electrolytes.

Blood Cells

Components of blood including erythrocytes, leukocytes, and thrombocytes (platelets).

Intracellular Fluid (ICF) Compartment

Fluid located inside the cells, accounting for approximately two thirds of total body fluid.

Extracellular Fluid (ECF) Compartment

Fluid located outside the cells, accounting for approximately one third of body fluid, and further divided into intravascular, interstitial, and transcellular spaces.

Intravascular Space

The fluid within the blood vessels that contains plasma; in adults, it accounts for approximately $3\,L$ of the average $6\,L$ of blood volume.

Interstitial Space

The area containing the fluid that surrounds the cells, totaling about $11$ to $12\,L$ in an adult; lymph is an example of fluid in this space.

Transcellular Space

The smallest division of the ECF compartment ($\approx 1\,L$), containing fluids such as cerebrospinal, pericardial, synovial, intraocular, and pleural fluids, as well as sweat and digestive secretions.

Third-Space Fluid Shift (Third Spacing)

The loss of ECF into a space (such as the peritoneal cavity or pleural space) that does not contribute to equilibrium between the ICF and ECF spaces.

Cations

Electrolytes in body fluids that carry positive charges, such as sodium, potassium, calcium, magnesium, and hydrogen ions.

Anions

Electrolytes in body fluids that carry negative charges, such as chloride, bicarbonate, phosphate, sulfate, and negatively charged protein ions.

Milliequivalent (mEq)

A measure of chemical activity defined as being equivalent to the electrochemical activity of $1\,mg$ of hydrogen.

Sodium ($Na^+$)

The most abundant cation in the ECF that regulates the volume of body fluid because water follows its movement.

Potassium ($K^+$)

One of the major electrolytes in the ICF; changes in its concentration in the ECF can cause cardiac rhythm disturbances or cardiac arrest.

Sodium–Potassium Pump

A cell membrane pump that expends energy to maintain high extracellular sodium levels and high intracellular potassium levels.

Osmosis

The diffusion of water through a selectively semipermeable membrane from a region of less concentrated solution to a more concentrated solution.

Osmolality

The number of milliosmoles of solute per kilogram of solvent ($mOsm/kg$); it is the preferred term for evaluating solutes in blood or urine.

Osmolarity

The number of milliosmoles per liter of solution ($mOsm/L$).

Hydrostatic Pressure

The pressure exerted by fluid on the walls of the blood vessel (also called hydraulic pressure) which pushes fluid out of the capillary toward the ICF.

Osmotic Pressure

The pressure exerted by the solutes within the plasma which pulls fluid into the capillary from the ICF.

Colloid Oncotic Pressure

Osmotic pressure specifically exerted by albumin within the bloodstream.

Crystalloid Solutions

Mineral ions dissolved in water, such as $0.9\%\text{ NaCl}$, $0.45\%\text{ NaCl}$, and lactated Ringer’s solution.

Colloid Solutions

Fluids containing nonsoluble substances evenly distributed in a solvent (volume expanders), such as albumin, dextran, or hyperoncotic starch.

Tonicity

The ability of solutes to cause an osmotic driving force that promotes water movement between compartments, determined by comparison to physiologic fluid ($0.9\%\text{ NaCl}$).

Isotonic Solutions

Solutions with the same sodium and chloride concentration as the bloodstream (e.g., $0.9\%\text{ NaCl}$) that expand plasma volume without provoking water movement between ICF and ECF.

Hypotonic Solutions

Solutions containing less solute but more water than the bloodstream (e.g., $0.45\%\text{ NaCl}$), used to move water from the ECF into the ICF to hydrate cells.

Hypertonic Solutions

Solutions with a greater concentration of $NaCl$ compared to blood (e.g., $3\%\text{ NaCl}$ or $5\%\text{ NaCl}$), used to pull water from the ICF into the ECF to treat cerebral edema or severe hyponatremia.

Mannitol

A nonresorbable sugar alcohol used as an IV solution to move water rapidly from the ICF to the ECF and induce osmotic diuresis, primarily to decrease cerebral edema.

Osmotic Diuresis

An increase in urine output caused by the excretion of solutes such as glucose or mannitol that pull water from the ICF into the bloodstream to be filtered by the kidneys.

$$5\%\text{ Dextrose in Water (D5W)}$$

An isotonic solution providing $170\,cal/L$ that converts to a hypotonic solution as dextrose is metabolized; used for hypernatremia and dehydration but contraindicated in head injuries.

Dextran

A colloid solution used as a plasma expander that affects clotting by coating platelets and is used to treat hypovolemia in early shock.