Module 4 Pathopharmacology: Fluid, Electrolyte, and Acid-Base Balance

Flashcards covering fluid and electrolyte balance, tonicity, IV fluids, electrolyte imbalances with normal lab values, cirrhosis, and diuretic pharmacology based on the Module 4 Learning Guide.

Electrolytes

A compound that forms ions whenever they are in a solution.

Intracellular fluid (ICF)

Fluid within the cell that accounts for 2/3 of body weight.

Extracellular fluid (ECF)

Fluid outside of the cell that accounts for 1/3 of body weight, including interstitial fluid, blood plasma, lymph, transcellular, and organ fluids.

Interstitial fluid

Fluid located between cells and outside of the blood vessels.

Membrane permeability

The degree to which a membrane allows substances to pass through it.

Semipermeable membrane

A membrane that allows some but not all molecules to pass.

Diffusion

The movement of substances from high concentration to low concentration until a uniform distribution is reached.

Osmosis

The movement of water molecules from low concentration to higher concentration.

Hydrostatic pressure

The pressure the fluid mass pushes outwards against its container.

Colloid osmotic pressure

The osmotic forces that influence fluid movement between the intracellular fluid (ICF) and extracellular fluid (ECF).

Tonicity

The ability of an extracellular solution to make water move in or out of a cell by osmosis.

Isotonic

A solution with an osmolarity of $275-295\,mOsm/kg$ that matches the blood; it treats the blood vessels by expanding volume and stabilizing blood pressure without altering cell size.

Hypertonic

A solution with an osmolarity $>295\,mOsm/kg$; it pulls water out of the cell and into the bloodstream, often used to treat dehydrated cells or brain swelling.

Hypotonic

A solution with an osmolarity $<275\,mOsm/kg$; it causes water to move into the cell, treating tissues and pulling excess fluid out of swollen tissues.

Osmolarity

The total concentration of all solutes in a solution; it is the property to which tonicity is related.

Lactated Ringers (LR)

An isotonic fluid used for dehydration, burns, hypovolemia, and diarrhea; it contains sodium, chloride, calcium, and lactate, but should be avoided in renal failure or liver disease.

D5W (Dextrose 5% in water)

A fluid used for fluid loss, dehydration, and hypernatremia; it is isotonic in the bag but becomes hypotonic as the cells use the dextrose for energy.

Normal Saline (0.9% sodium chloride)

An isotonic fluid used for shock, hyponatremia, fluid challenges, metabolic alkalosis, hypercalcemia, and DKA; it is the only fluid that can be infused with blood products.

D5 ½ NS (Dextrose 5% in half normal saline)

A hypertonic fluid used for DKA and the prevention of hypoglycemia and cerebral edema.

D5 NS (Dextrose 5% in normal saline)

A hypertonic fluid used for shock, SIADH, and Addisonian crisis; contraindicated in cardiac or renal patients due to the danger of heart failure and pulmonary edema.

3% NaCl

A hypertonic, high-alert saltwater used for critical hyponatremia and cerebral edema; must be infused slowly via a central line to avoid central pontine myelinolysis.

0.45% sodium chloride (half-normal saline)

A hypotonic fluid used for water replacement, sodium and chloride depletion, and diabetes insipidus; it may increase intracranial pressure.

Third spacing of fluids

A condition where too much fluid moves from the intravascular space to the interstitial space, leading to edema, hypotension, and potentially cardiac arrest.

Edema

The palpable swelling caused by the accumulation of fluid in interstitial spaces from the vascular space; causes include decreased oncotic pressure and increased capillary permeability.

Sodium ($Na^+$) Lab Value

The normal range is $135-145\,meq/l$; changes primarily affect the brain, causing confusion, lethargy, or seizures.

Potassium ($K^+$) Lab Value

The normal range is $3.5-5.0\,meq/l$; it is responsible for nerve impulse conduction and muscle contraction, and imbalances are cardiotoxic.

Calcium ($Ca^{2+}$) Lab Value

The normal range is $9.0-10.5\,mg/dl$; it is essential for bone/teeth and regular muscle contraction.

Chvostek’s sign

A sign of hypocalcemia characterized by twitching of the facial muscle in response to tapping over the area of the facial nerve.

Trousseau sign

A sign of hypocalcemia characterized by a carpopedal spasm caused by inflating a blood pressure cuff above systolic pressure for 3 minutes.

Magnesium ($Mg^{2+}$) Lab Value

The normal range is $1.3-2.1\,meq/L$; it acts as a muscle relaxant and regulates neuromuscular function.

Phosphate ($PO_4^{3-}$) Lab Value

The normal range is $3.0-4.5\,mg/dl$; it typically has an inverse relationship with calcium levels.

Cirrhosis

Late-stage hepatic fibrosis resulting in widespread distortion of hepatic architecture, characterized by regenerative nodules and dense fibrotic tissue.

Ascites

The accumulation of fluid in the abdominal cavity, a common late manifestation of cirrhosis.

Hydrochlorothiazide

A Thiazide diuretic prototype that increases excretion of $Na^+$, $Cl^-$, $K^+$, and $Mg^{2+}$ while decreasing calcium excretion; used for hypertension and edema.

Furosemide

A Loop diuretic prototype that works in the Loop of Henle to promote excretion of sodium, chloride, water, and potassium; can cause ototoxicity if infused rapidly via IV.

Spironolactone

A Potassium-sparing diuretic prototype that increases diuresis and decreases edema while maintaining potassium levels; interacts toxically with digoxin and lithium.

Mannitol

An osmotic diuretic used to manage oliguria/anuria and decrease intracranial pressure by pulling water from extravascular sites into the bloodstream.