Fluid and Electrolyte Overview

Vocabulary flashcards covering core concepts of fluid and electrolyte balance, fluid spacing, endocrine and renal responses, hemodynamics, and IV fluid classifications.

Intracellular Fluid (ICF)

Also known as cytosol or cytoplasm, it is the fluid located inside cells that contains water, proteins, dissolved solutes, potassium, magnesium, and phosphorus.

Extracellular Fluid (ECF)

Fluid located outside of cells composed of intravascular plasma and interstitial fluid, containing dissolved solutes such as sodium, chloride, bicarbonate, and calcium.

Osmosis

The movement of water across a semi-permeable cell membrane from an area of low solute concentration to an area of high solute concentration.

Hydrostatic Pressure

The force of fluid against vessel walls that squeezes fluid out of the plasma (vascular system) into surrounding tissues.

Oncotic Pressure

The pressure that forces fluid from the surrounding tissue back into the plasma (vascular system).

Osmolality

The number of solutes per kilogram (weight) of water.

Osmolarity

The number of solutes per liter (volume) of solution.

Serum Osmolarity Normal Range

The normal concentration of solutes in blood serum, measured between $270\text{--}300\text{ mOsm/L}$.

First Spacing

Normal fluid distribution between intracellular fluid (ICF) and extracellular fluid (ECF) compartments achieving homeostasis.

Second Spacing

An accumulation of excess fluid in the interstitial space, such as peripheral edema, that can still be mobilized and reabsorbed by the body.

Third Spacing

Fluid trapped in body compartments where it is inaccessible to maintain normal fluid balance, such as in ascites or blisters.

Anti-Diuretic Hormone (ADH)

Also called vasopressin, a hormone released by the pituitary gland in response to high osmolarity or low volume detected by baroreceptors.

Renin

A peptide hormone released by the kidneys in response to low blood pressure or low sodium levels to initiate the RAAS cycle.

Mean Arterial Pressure (MAP)

An indicator of perfusion calculated using the formula $\text{MAP} = \frac{2(\text{DBP}) + \text{SBP}}{3}$, with normal levels ranging between $70\text{--}110\text{ mmHg}$.

Hypotonic Solution

An IV solution with an osmolarity less than $270\text{ mOsm/L}$ that causes fluid to shift from the intravascular space into cells, causing cells to swell.

Isotonic Solution

An IV solution with an osmolarity equal to body fluids ($270\text{--}300\text{ mOsm/L}$) that expands intravascular volume without shifting fluid into or out of cells.

Hypertonic Solution

An IV solution with a high solute concentration that shifts fluid from cells into the intravascular lumen.

Colloid

A plasma volume expander, such as Albumin, that pulls fluid from interstitial (2nd) space into the intravascular space.

0.45% Normal Saline

A hypotonic IV solution with an osmolarity less than $270\text{ mOsm/L}$ ($77\text{ mEq/L}$ $Na^+$ and $77\text{ mEq/L}$ $Cl^-$) used as a maintenance fluid.

0.9% Normal Saline

An isotonic IV solution with an osmolarity of $308\text{ mOsm/L}$ that is compatible with blood products, antibiotics, potassium, and insulin.

Lactated Ringer's (LR)

An isotonic IV solution with an osmolarity of $273\text{ mOsm/L}$ containing sodium, chloride, potassium, calcium, and lactate, which is NOT compatible with blood products.

5% Dextrose in Water (D5W)

An IV solution that is isotonic in the bag but becomes hypotonic inside the body once glucose is metabolized.

3% NaCl

A hyperosmotic (hypertonic) IV solution administered via a central line for severe or symptomatic hyponatremia to reduce cerebral edema.