Electrolytes Calculators

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Electrolytes are ions dissolved in body fluids that carry electrical charges and perform essential physiological functions — from maintaining membrane potential in neurons to regulating fluid balance and muscle contraction. The major electrolytes in the human body are sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), bicarbonate (HCO₃⁻), calcium (Ca²⁺), magnesium (Mg²⁺), and phosphate (PO₄³⁻). Electrolyte balance is tightly regulated by the kidneys, hormones, and multiple feedback systems, and disturbances can have life-threatening consequences.

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What Are Electrolytes?

Electrolytes are substances that dissociate into ions when dissolved in water, enabling the solution to conduct electricity. In biological contexts, electrolytes are the ions present in blood plasma, interstitial fluid, and intracellular fluid that maintain osmotic pressure, support nerve and muscle function, regulate pH, and enable enzymatic reactions.

Major Electrolytes and Their Functions

Sodium (Na⁺) — Normal range: 136–145 mEq/L

The primary extracellular cation. Sodium controls extracellular fluid volume and osmolality — water follows sodium. The Na⁺/K⁺-ATPase pump maintains the steep Na⁺ gradient that drives action potentials in neurons and muscles.

Potassium (K⁺) — Normal range: 3.5–5.0 mEq/L

The primary intracellular cation (~140 mEq/L inside cells). The K⁺ gradient across cell membranes establishes the resting membrane potential. Critical for cardiac rhythm — hypo- or hyperkalemia causes potentially fatal arrhythmias.

Chloride (Cl⁻) — Normal range: 98–106 mEq/L

Major extracellular anion, closely follows sodium. Important for maintaining electrical neutrality and producing stomach acid (HCl).

Bicarbonate (HCO₃⁻) — Normal range: 22–29 mEq/L

The primary buffer of blood pH (bicarbonate buffer system). Regulated by the kidneys and respiratory system to maintain blood pH 7.35–7.45.

Calcium (Ca²⁺) — Normal range: 8.5–10.5 mg/dL (total)

Required for muscle contraction (including cardiac muscle), nerve transmission, blood clotting, and bone mineralization. Most calcium is bound to albumin; ionized Ca²⁺ is the biologically active form.

Magnesium (Mg²⁺) — Normal range: 1.7–2.2 mg/dL

Cofactor for hundreds of enzymes, including all ATPases and kinases. Required for DNA replication, protein synthesis, and neuromuscular function.

Osmolality and Electrolytes

Plasma osmolality (normal: 275–295 mOsm/kg) is primarily determined by sodium:

Estimated osmolality = 2[Na⁺] + glucose/18 + BUN/2.8

Sodium accounts for approximately 90% of extracellular osmolality. Osmolality is monitored by hypothalamic osmoreceptors and regulated via ADH (antidiuretic hormone) and thirst.

Electrolyte Imbalances

  • Hyponatremia (Na⁺ <136): Confusion, seizures, coma — often from overhydration or SIADH
  • Hyperkalemia (K⁺ >5.5): Cardiac arrhythmias, peaked T waves on ECG — emergency
  • Hypocalcemia (Ca²⁺ <8.5): Tetany, muscle cramps, paresthesias, prolonged QT interval

Glossary

Electrolyte
An ion dissolved in body fluids (Na⁺, K⁺, Cl⁻, HCO₃⁻, Ca²⁺, Mg²⁺, PO₄³⁻) that carries electrical charge and is essential for osmotic regulation, nerve and muscle function, pH buffering, and enzymatic activity.
Osmolality
The concentration of solute particles per kilogram of solvent, expressed in mOsm/kg. Plasma osmolality (275–295 mOsm/kg) is primarily determined by sodium and is the key driver of water movement between body compartments.
Hyponatremia
A serum sodium concentration below 136 mEq/L. Causes water to shift into brain cells (cerebral edema), producing symptoms ranging from nausea and headache to confusion, seizures, and coma in severe cases.

Frequently Asked Questions

The major electrolytes are: sodium (Na⁺, 136–145 mEq/L — primary extracellular cation), potassium (K⁺, 3.5–5.0 mEq/L — primary intracellular cation), chloride (Cl⁻, 98–106 mEq/L), bicarbonate (HCO₃⁻, 22–29 mEq/L), calcium (Ca²⁺), magnesium (Mg²⁺), and phosphate (PO₄³⁻). Each has distinct distribution and physiological roles.

Potassium is critical for maintaining the resting membrane potential of cardiac cells (-90 mV). The K⁺ gradient (high inside, low outside) drives K⁺ out of cells through leak channels, generating the negative resting potential. Hypokalemia (low K⁺) makes cells more excitable — causing arrhythmias and PVCs. Hyperkalemia (high K⁺) reduces the gradient, depolarizes membranes, and can cause life-threatening ventricular fibrillation.

Common causes include: excessive sweating (sodium, potassium, chloride loss); vomiting and diarrhea (sodium, potassium, chloride, bicarbonate loss); kidney disease (impaired regulation of all electrolytes); hormonal disorders (Conn syndrome — excess aldosterone causing hypernatremia/hypokalemia; Addison's disease — opposite pattern); certain medications (diuretics, ACE inhibitors); and overhydration or dehydration.

Sports drinks contain sodium, potassium, and chloride — the electrolytes lost primarily in sweat — along with carbohydrates for energy. Sodium replacement is most important for endurance athletes (>1 hour of exercise) because sweat sodium losses can be significant. Simple water rehydration without sodium replacement can cause hyponatremia (exercise-associated hyponatremia) in prolonged events. Most sports drinks contain 20–30 mEq/L sodium and 5–10 mEq/L potassium.