Lesson 7: Sodium

Sodium Overview

  • Normal Serum Sodium Value: 135 - 145 mEq/L.

  • Role of Sodium:

    • Sodium is the primary determinant of serum osmolarity.
    • It plays a significant role in regulating extracellular fluid (ECF) volume through osmotic forces.

  • Regulation of Sodium Homeostasis:

    • Factors involved in sodium homeostasis include:
    • Glomerular filtration rate
    • Renin-angiotensin-aldosterone system
    • Antinatriuretic peptides (e.g., BNP - B-type Natriuretic Peptide)

  • Correction of Sodium Disorders:

    • Disorders of sodium balance must be corrected slowly; no faster than 1 - 2 mEq/L/hr.
    • Rapid treatment of hyponatremia can cause fluid to shift from intracellular fluid (ICF) to extracellular fluid (ECF), potentially leading to central pontine myelinolysis.
    • Rapid treatment of hypernatremia can cause fluid to shift from ECF to ICF, resulting in cerebral edema.

  • Administration of 3% Saline:

    • When treating hyponatremia with 3% saline, the serum sodium concentration should not increase faster than a defined rate (e.g., enter specific mEq/L/hr).

Disorders of Sodium Balance

Etiology

Hyponatremia (< 135 mEq/L)

  • States of Hydration:

    • Hyponatremia may occur in various states: hypovolemic, isovolemic, and hypervolemic.
    • It is crucial to evaluate plasma osmolarity and ECF volume to determine the underlying cause.

  • Causes by Total Body Sodium Content:

    • Decreased Total Body Na+ Content:

    • Diuretics

    • Salt-wasting diseases

    • Hypoaldosteronism (can also be associated with Hyperkalemia)

    • Normal Total Body Na+ Content:

    • SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion)

    • Hypothyroidism

    • Water intoxication

    • Perioperative stress

    • Increased Total Body Na+ Content:

    • Congestive Heart Failure (CHF)

    • Cirrhosis

Presentation Based on Plasma Sodium Concentration:

  • 130 - 135 mEq/L:

    • No signs to mild signs.

  • 125 - 129 mEq/L:

    • Symptoms include nausea (N/V) and malaise.

  • 115 - 124 mEq/L:

    • Symptoms include headache, lethargy, and altered level of consciousness (LOC).

  • 115 mEq/L or less (or rapid onset):

    • Severe symptoms such as seizures, coma, cerebral edema, and respiratory arrest.

  • Treatment:

    • Treatment depends on the specific cause.
    • Goal is to restore Na+ balance by managing serum osmolality and fluid balance:
    • Water restriction
    • Intravenous fluid (IVF) selection based on tonicity
    • Diuretics
Hypernatremia (> 145 mEq/L)

  • States of Hydration:

    • Hypernatremia may also exist in various hydration states: hypovolemic, isovolemic, and hypervolemic.
    • Evaluation of plasma osmolarity and ECF volume is essential for determining the cause.

  • Causes by Total Body Sodium Content:

    • Decreased Total Body Na+ Content:

    • Osmotic diuresis

    • Nausea and vomiting (N/V)

    • Adrenal insufficiency

    • Normal Total Body Na+ Content:

    • Diabetes insipidus

    • Renal failure

    • Diuretics

    • Increased Total Body Na+ Content:

    • Hyperaldosteronism

    • Increased sodium intake (e.g., 3% saline)

  • Normal Serum Osmolality Range:

    • Normal serum osmolality is typically between 280 - 290 mOsm/kg.
Hypernatremia Presentation Based on Serum Osmolality:

  • 350 - 375 mOsm/kg:

    • Symptoms include headache, agitation, confusion.

  • 376 - 400 mOsm/kg:

    • Weakness, tremors, ataxia are observed.

  • 401 - 430 mOsm/kg:

    • Symptoms include hyperreflexia and muscle twitching.

  • 431 mOsm/kg or more:

    • Severe symptoms such as seizures, coma, and potentially death.

  • Treatment:

    • Treatment is contingent on the specific underlying cause.
    • The goal is to restore Na+ balance by manipulating serum osmolality and fluid balance:
    • Sodium (Na+) restriction
    • IVF selection based on tonicity
    • Diuretics

Important Notes

  • Both extremes of sodium disorders (hyponatremia and hypernatremia) should be corrected slowly (no faster than 1 - 2 mEq/L/hr).
  • Rapid correction of either disorder can result in severe neurological complications:
    • Treating hyponatremia too quickly can lead to central pontine myelinolysis.
    • Treating hypernatremia too quickly can lead to cerebral edema.