Fluid and Electrolyte Balance Lecture Notes

Flashcards covering fluid and electrolyte balance, including body compartments, transport mechanisms, and various IV solution types.

Solvent

The substance, usually a liquid, that does the dissolving to create a uniform, homogeneous mixture (e.g., water).

Solute

The substance that is being dissolved in a liquid, gas, or solid (e.g., sugar, sodium, potassium).

Solution

A uniform, homogeneous mixture of two or more substances, consisting of a solute (smaller amount) and a solvent (larger amount).

Homeostasis

The maintenance of a constant internal equilibrium in a biologic system, essential for sustaining life.

Total Body Weight (TBW)

The total amount of water in the body, constituting $50-60\%$ of total body weight in adults and $80\%$ in newborns.

Intracellular Space (ICF)

The fluid found inside the cells, accounting for approximately $2/3$ of total body fluid or $40\%$ of total body weight ($28\,L$ in a $70\,kg$ male).

Extracellular Space (ECF)

The fluid found outside the cells, accounting for approximately $1/3$ of total body fluid or $20\%$ of total body weight ($14\,L$). IT is divided into intravascular, interstitial, and transcellular spaces.

Intravascular Space

The fluid found within the blood vessels, specifically the plasma, which makes up about $5\%$ of TBW ($3.5\,L$).

Interstitial Space

The space containing the fluid that surrounds the cell, accounting for $15\%$ of TBW ($10.5\,L$).

Transcellular Fluid Spaces

The smallest division of the ECF, including fluids such as saliva, sweat, cerebrospinal, synovial, intraocular, and pleural fluids.

Osmosis

The movement of solvent molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Diffusion

The net movement of particles (atoms, molecules, ions) from a region of higher concentration to a region of lower concentration until equalization occurs.

Active Transport

A cellular process that moves molecules across the cell membrane against their concentration gradient (low to high), requiring energy in the form of ATP.

Primary Active Transport

A type of transport where the movement of molecules is directly powered by ATP hydrolysis, such as the $Na^+-K^+$ pump.

Secondary Active Transport

A process where the transport of a substance (like glucose) against its gradient is driven by the energy stored in the concentration gradient of another ion (like $Na^+$).

Nutrient Solutions

IV solutions containing carbohydrates (e.g., dextrose, glucose) and water, used to supply calories, prevent dehydration, and prevent ketosis.

Electrolyte Solutions

IV solutions containing varying amounts of cations and anions used to replace fluid and electrolytes for clients with continuing losses (e.g., $0.9\%\,NaCl$, Ringer's Solution).

Alkalinising Solutions

Solutions administered to treat metabolic acidosis, such as Lactated Ringer's Solution (LRS).

Acidifying Solutions

Solutions used to counteract metabolic alkalosis, such as $D51/2NS$ and $0.9\%\,NaCl$.

Volume Expanders

Solutions used to increase blood volume after severe blood or plasma loss, including dextran, human albumin, and plasma.

Crystalloid Solution

Solutions with a short half-life ($30-60\,min$) containing small molecules that freely cross capillary walls; excessive use can cause peripheral and pulmonary edema.

Colloid Solution

Solutions with a half-life of several hours/days containing large molecules that remain in the intravascular space, used for volume-for-volume replacement.

Isotonic Solutions

Solutions with the same osmolality as body fluids, intended to expand ECF volume, such as $0.9\%\,NaCl$ ($308\,mOsm/L$) and Lactated Ringer's ($273\,mOsm/L$).

Hypotonic Solutions

Solutions with lower osmolality than body fluids, used to replace water and treat hypernatremia, such as $0.45\%\,NaCl$ ($154\,mOsm/L$).

Hypertonic Solutions

Solutions with higher osmolality than body fluids, used for severe hyponatremia or cerebral edema, such as $3\%\,NaCl$ ($1030\,mOsm/L$) or $D50W$ ($2523\,mOsm/L$).

Dextrose 5% in Water (D5W)

Initially isotonic ($252\,mOsm/L$) solution that becomes hypotonic as dextrose is metabolized, used to treat hypernatremia and provide free water.

Normal Saline Solution (NSS)

An isotonic solution of $0.9\%\,NaCl$ containing $154\,mEq/L$ of Sodium and Chloride, used for ECF volume expansion and alongside blood products.

Lactated Ringer's Solution (LRS)

An isotonic solution ($273\,mOsm/L$) containing sodium, potassium, calcium, chloride, and lactate, used to correct dehydration and metabolic acidosis.