Fluid Balance & Electrolyte Imbalances

Comprehensive vocabulary flashcards covering fluid compartments, tonicity, diagnostic fluid status parameters, and electrolyte imbalances.

Homeostasis

The state of equilibrium in the internal environment of the body, naturally maintained by keeping the composition and volume of body fluids within narrow limits of normal.

Intracellular Fluid (ICF)

Fluid located within cells that constitutes $42\%$ of total body weight (or approximately $67\%$ of total body fluid), in which potassium ($\text{K}^+$) is the most prevalent cation and phosphate ($\text{PO}_4^-$) is the most prevalent anion.

Extracellular Fluid (ECF)

Body fluid outside cells divided into interstitial fluid ($2/3$ of ECF) and intravascular plasma ($1/3$ of ECF), where sodium ($\text{Na}^+$) is the major cation and chloride ($\text{Cl}^-$) is the major anion.

Transcellular Fluid

A specialized fluid compartment of approximately $1\,\text{L}$ that includes cerebrospinal, gastrointestinal, pleural, synovial, and peritoneal fluids.

Hypotonic Solution

A solution with a lower solute concentration than the cell (e.g., $0.45\%\,\text{NaCl}$, $0.33\%\,\text{NaCl}$, $2.5\%$ Dextrose in water) that causes water to move into cells, resulting in swelling or potential lysis.

Hypertonic Solution

A solution with a higher solute concentration than the cell (e.g., $3\%\,\text{NaCl}$, $5\%\,\text{NaCl}$, $10\%$ Dextrose in water, Mannitol) that draws water out of cells into the ECF, causing cells to shrink (crenation).

Isotonic Solution

A solution possessing the same solute concentration as the cell (e.g., $0.9\%\,\text{NaCl}$, Lactated Ringer's, $5\%$ Dextrose in water, Plasma-Lyte), causing no net water shift and keeping cell size constant.

Osmolality

A measure of solute concentration per kilogram of solvent ($\text{mOsm/kg}$) evaluated in blood ($280\text{--}300\,\text{mOsm/kg}$) and urine ($200\text{--}800\,\text{mOsm/kg}$), serving as the clinical gold standard for fluid concentration.

Osmolarity

The concentration of an osmotic solution expressed per liter of solution ($\text{mOsm/L}$), commonly referenced when describing intravenous (IV) fluids.

Urine Specific Gravity

A measurement ($1.010\text{--}1.025$) reflecting the kidney's ability to excrete or conserve water, varying inversely with urine volume.

Blood Urea Nitrogen (BUN)

The end product of protein metabolism from muscle and dietary intake with a normal range of $10\text{--}20\,\text{mg/dL}$ ($3.6\text{--}7.02\,\text{mmol/L}$), which elevates in dehydration, gastrointestinal bleeding, fever, and sepsis.

Creatinine

The end product of muscle metabolism with a normal level of $0.7\text{--}1.4\,\text{mg/dL}$ ($62\text{--}124\,\mu\text{mol/L}$), serving as a more reliable indicator of renal function than BUN because it increases as renal function decreases.

Hematocrit

The volume percentage of red blood cells in whole blood, normally measuring $42\%\text{--}52\%$ in males and $35\%\text{--}47\%$ in females.

Fluid Volume Deficit (FVD)

Hypovolemia occurring when the loss of extracellular fluid exceeds intake, with water and electrolytes lost in proportional balance to normal body fluids.

Dehydration

The loss of body water alone, accompanied by an increased serum sodium level, which may occur in isolation or with other electrolyte imbalances.

Fluid Volume Excess (FVE)

Hypervolemia defined by an abnormal expansion of the extracellular fluid compartment due to the retention of water and sodium.

Sodium ($\text{Na}^+$)

The primary extracellular cation (normal range: $135\text{--}145\,\text{mEq/L}$) responsible for regulating ECF volume, maintaining osmolality, transmitting nerve impulses, and maintaining acid-base balance.

Hypernatremia

A serum sodium level exceeding $145\,\text{mEq/L}$ caused by water deficit or sodium excess, leading to cellular dehydration, thirst, lethargy, agitation, seizures, and potential coma.

Hyponatremia

A serum sodium concentration below $135\,\text{mEq/L}$ resulting from sodium-containing fluid loss or water excess, manifesting with confusion, nausea, vomiting, seizures, and coma.

Potassium ($\text{K}^+$)

The primary intracellular cation (normal range: $3.5\text{--}5.5\,\text{mmol/L}$) essential for neuromuscular transmission, maintaining normal cardiac rhythms, skeletal muscle contraction, and acid-base regulation.

Hyperkalemia

A serum potassium level above $5.5\,\text{mmol/L}$ characterized by impaired cardiac depolarization, accelerated repolarization, ventricular fibrillation, muscle weakness, and diarrhea.

Hypokalemia

A serum potassium level below $3.5\,\text{mmol/L}$ caused by increased renal or GI excretion, manifesting as potentially lethal ventricular arrhythmias, muscle breakdown (myoglobinuria), and heightened digoxin toxicity.

Calcium ($\text{Ca}^{2+}$)

An essential mineral (normal range: $8.6\text{--}10.2\,\text{mg/dL}$) concentrated largely in bones ($>99\%$), holding an inverse relationship with phosphorus and stabilizing cell membranes by blocking sodium influx.

Hypercalcemia

A serum calcium concentration exceeding $10.2\,\text{mg/dL}$ (often $> 11\,\text{mg/dL}$) commonly caused by hyperparathyroidism or malignancy, manifesting with impaired memory, confusion, disorientation, and fatigue.

Hypocalcemia

A serum calcium deficit presenting with increased neuromuscular excitability, laryngeal stridor, circumoral numbness, paresthesias, positive Chvostek's sign, and positive Trousseau's sign.

Chvostek's Sign

A physical assessment sign of hypocalcemia characterized by involuntary twitching or contraction of the facial muscles elicited by tapping the facial nerve anterior to the ear.

Trousseau's Sign

A physical indicator of hypocalcemia manifesting as a carpal spasm when a blood pressure cuff is inflated above systolic blood pressure for a few minutes.

Magnesium ($\text{Mg}^{2+}$)

The second most abundant intracellular cation (normal range: $1.3\text{--}2.3\,\text{mg/dL}$ or $0.62\text{--}0.95\,\text{mmol/L}$) necessary for carbohydrate and protein metabolism and the regulation of neuromuscular contractility.

Hypomagnesemia

A serum magnesium concentration below $1.3\,\text{mg/dL}$ resulting from alcoholism or GI losses, presenting with neuromuscular irritability, tremors, dysphagia, athetoid movements, and ECG dysrhythmias.

Hypermagnesemia

An elevated serum magnesium state typically caused by renal failure or excessive administration, characterized by flushing, hypotension, hypoactive reflexes, drowsiness, and respiratory depression.