Fluid and Electrolytes Flashcards

Intracellular Fluid (ICF)

Fluid contained inside cells; major cation is potassium and major anion is phosphate; represents about 40% of body weight.

Extracellular Fluid (ECF)

Fluid outside cells; major cation is sodium and major anion is chloride; includes plasma; about 20% of body weight.

Cations

Electrolyte particles with a positive charge (e.g., Na+, K+, Ca2+, Mg2+).

Anions

Electrolyte particles with a negative charge (e.g., chloride, bicarbonate, phosphate).

Electrolytes

Chemicals in body fluids that dissociate into ions and carry charge; essential for fluid balance and nerve/muscle function.

Sodium

Major extracellular cation; regulates water distribution and fluid volume; normal serum 135–145 mEq/L.

Potassium

Major intracellular cation; essential for skeletal and cardiac muscle activity and nerve function; normal serum 3.5–5 mEq/L.

Sodium-Potassium Pump

Active transport that maintains the Na+/K+ gradient; Na+ moves out of cells and K+ moves in to depolarize and repolarize membranes.

Hyponatremia

Low extracellular sodium (often <135 mEq/L); can be hypovolemic, euvolemic, or hypervolemic; presents with neuro and non-neuro symptoms.

Hypernatremia

High extracellular sodium (>145 mEq/L); often due to water loss or excessive sodium intake; can cause dehydration and CNS symptoms; requires gradual correction.

ADH (Vasopressin)

Antidiuretic hormone; promotes water reabsorption in kidneys; released when blood volume/pressure is low; imbalances cause SIADH or DI.

SIADH

Syndrome of Inappropriate Antidiuretic Hormone; excessive ADH leading to water retention and hyponatremia.

Diabetes Insipidus (DI)

Condition of deficient ADH leading to large volumes of dilute urine and risk of hypernatremia.

Osmosis

Movement of water across a semipermeable membrane from lower to higher solute concentration.

Diffusion

Movement of solutes from higher to lower concentration across membranes.

Isotonic Solution

Solution with osmolality similar to plasma; does not cause net water movement; used to replace volume without shifting water.

Hypotonic Solution

Solution with lower osmolality than plasma; causes water to move into cells (e.g., 0.45% NaCl).

Hypertonic Solution

Solution with higher osmolality than plasma; draws water out of cells; examples include 3% NaCl, D10W, D5NS, D5LR (given slowly).

Capillary Filtration Pressure

Hydrostatic pressure that pushes water out of capillaries into the interstitial space; influenced by blood pressure and gravity.

Capillary Colloid Osmotic Pressure

Osmotic pull back into capillaries driven by plasma proteins (e.g., albumin, globulins).

Interstitial Hydrostatic Pressure

Hydrostatic pressure in the interstitial space that resists capillary filtration and pushes water back toward capillaries.

Transcellular Fluid

Small, specialized fluid compartments (CSF, pleural, peritoneal, intraocular) totaling about 1 liter.

Lymphatic System

Transports interstitial fluid back to vascular circulation; removes plasma proteins from tissue spaces; helps manage edema.

Edema

Swelling due to excess interstitial fluid; can be localized or generalized (anasarca); dependent edema; lymphedema from impaired lymph flow.

Second Space Edema

Fluid shift into nonfunctional spaces (e.g., peritoneal, pleural) making fluid unavailable for circulatory use.

Third Space

Accumulation of trapped extracellular fluid in a body space that normally does not hold fluid (e.g., ascites, effusions).

Fluid Volume Deficit (FVD)

Loss of body fluids due to GI losses, renal losses (diuretics), vascular losses, skin losses (burns), or inadequate intake.

FRIED SALT

Signs of hypernatremia: F - Flushed skin; R - Restless; I - Increased BP and fluid retention; E - Edema; D - Decreased urine output; S - Skin dry; A - Agitation; L - Low-grade fever; T - Thirst.

SALT LOST

Signs of hyponatremia: S - Stupor/coma; A - Anorexia; L - Lethargy; T - Tachycardia; L - Limp muscles; O - Orthostatic hypotension; S - Seizures/headache; S - Stomach cramping; T - Thirst.

Renin-Angiotensin-Aldosterone System (RAAS)

Hormonal system that regulates sodium reabsorption, blood pressure, and blood volume via renin, angiotensin II, and aldosterone.

Osmolarity

Concentration of solutes per liter of solution (measured in mOsm/L).

Total Body Water (TBW)

Approximately 60% of body weight; intracellular fluid ~40% and extracellular fluid ~20% of body weight.

0.9% Normal Saline (Isotonic)”

Isotonic fluid used to replace volume; contains sodium and chloride; commonly used for fluid resuscitation.

Lactated Ringers (LR)

Isotonic balanced electrolyte solution used for fluid resuscitation and to replace losses.

D5W (5% Dextrose in Water)

Causes isotonic distribution in IV fluids but becomes hypotonic once metabolized; used for gentle rehydration in some contexts.

Hypocalcemia

Low serum calcium; can cause paresthesias, cramps, tetany.

Hypercalcemia

High serum calcium; can cause weakness, confusion, bradycardia.

Hypomagnesemia

Low magnesium; can cause neuromuscular irritability, tremors, arrhythmias.

Hypermagnesemia

High magnesium; can cause hyporeflexia, hypotension, bradycardia.

Hypophosphatemia

Low phosphate; can affect energy metabolism and muscle function.

Hyperphosphatemia

High phosphate; often associated with hypocalcemia and renal dysfunction.