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Interstitial fluid: Interstitial fluid is the ECF that surrounds cells (fluid in tissue spaces). It is outside the blood vessels; plasma is inside the blood vessels.

Intracellular fluid: Intracellular fluid is the fluid inside cells (largest compartment). Plasma is extracellular and intravascular, not intracellular.

40% of total body fluid: Rough approximations: total body water ≈ 60% of body weight; intracellular ≈ 2/3 of TBW, extracellular ≈ 1/3. Plasma is only a portion of the ECF (about ~5% of body weight, roughly 20–25% of the ECF), not 40% of TBW.

Diffusion is the passive movement of solute particles from an area of higher concentration to an area of lower concentration (down their concentration gradient). It refers to solute movement, not solvent movement specifically.

Active transport moves substances against their concentration gradient and requires energy (ATP) - e.g., the Na⁺/K⁺ pump. It’s not the passive movement of water from low to high solute concentration.

Filtration is movement of fluid and solutes across a membrane driven by hydrostatic pressure (for example, blood pressure forcing plasma across glomerular membranes). It’s pressure-driven, not osmosis.

The chief electrolyte of extracellular fluid: Sodium (Na⁺) is the chief extracellular electrolyte/cation, not potassium.

The most abundant electrolyte in the body: Potassium is the major intracellular cation and, by total body content (because the intracellular compartment is large), potassium is present in large amounts

The chief extracellular anion: Chloride (Cl⁻) is the chief extracellular anion; potassium is a cation and is primarily intracellular.

Intake and output: I&O monitoring is important, but it’s subject to recording errors, misses insensible losses (sweat, respiration), and doesn’t account for fluid shifts between compartments. It’s helpful trend data but less precise than weight.

Skin turgor: Skin turgor can be affected by age, nutrition, and skin elasticity; it’s a supportive physical sign but insensitive for small changes in total body fluid.

Complete blood count: Hematocrit/hemoglobin can reflect hemoconcentration or hemodilution but are influenced by bleeding, anemia, transfusion, and other factors; they’re not the best single indicator of fluid balance.

Renal: The kidneys participate in calcium balance (via reabsorption and vitamin D activation), but immediate nursing interventions for hypocalcemia are less often renal-directed. Renal issues are important for long-term calcium management but are not the highest acute priority.

Gastrointestinal: GI symptoms (nausea, abdominal cramps) can occur with electrolyte disturbances, but they are not the most urgent systems to monitor for acute hypocalcemic complications.

Neuromuscular: Hypocalcemia commonly causes paresthesias, muscle cramps, tetany, and positive Chvostek/Trousseau signs. These are important and potentially severe (e.g., laryngospasm), but cardiac complications take precedent because they are immediately life-threatening.