Sodium Disorders Lecture Notes

Introduction

• Discussion on sodium disorders: Hyponatremia and Hypernatremia.
• Part of the clinical medicine section.
• Encouragement to engage with content and use supplemental resources available on website.

Hyponatremia

• Definition: Sodium level less than 135 meq/L.

Pathophysiology

• Water vs. Sodium: Excess water relative to sodium, often due to increased ADH (antidiuretic hormone).
• ADH Regulation:
  • Secreted under low blood volume/pressure conditions through renin-angiotensin system.
  • Stimulates water reabsorption in kidneys, increasing blood volume and diluting sodium.

Urine Osmolality

• High urine osmolality indicates high ADH levels.
• Appropriate ADH Increase: Low blood volume/pressure.
• Inappropriate ADH Increase (SIADH): Unrelated to blood pressure/volume; caused by diseases, drugs, etc.

ADH Suppression

• High water intake or low solute intake suppresses ADH.
• Results in high urine output and low urine osmolality.

Volume Assessment

• Categorize into hypovolemic, euvolemic, and hypervolemic states.
• Hypovolemic Hyponatremia: Sodium loss greater than water loss; caused by diuretics, adrenal insufficiency, etc.
• Euvolemic Hyponatremia: Often SIADH; normal blood volume, excessive ADH production.
• Hypervolemic Hyponatremia: High total body water and sodium, conditions like CHF and cirrhosis.

Hypernatremia

• Definition: Sodium level greater than 145 meq/L.

Pathophysiology

• Decreased ADH Release: Central or nephrogenic diabetes insipidus.
• High Aldosterone Levels: Results from adrenal tumors or excessive RAS activation.

Water Loss

• Causes include renal (diuretics) and extrarenal (sweating, diarrhea) sources.
• Insufficient water consumption exacerbates condition.

Volume Assessment

• Hypovolemic Hypernatremia: Water loss greater than sodium loss; treat with fluid resuscitation and free water.
• Euvolemic Hypernatremia: ADH dysfunction; treat with desmopressin or thiazides.
• Hypervolemic Hypernatremia: High sodium intake; treat with loop diuretics.

Complications

Hyponatremia

• Cerebral Edema: Water influx into brain tissue; causes increased intracranial pressure.
• Osmotic Demyelination Syndrome: Rapid correction of sodium leads to pontine demyelination.

Hypernatremia

• Cerebral Edema: Occurs if sodium is corrected too quickly (>12 meq/L in 24 hours).

Management

Hyponatremia

• Acute/Symptomatic: Hypertonic saline to manage cerebral edema or seizures.
• Hypovolemic: Normal saline to restore volume and sodium.
• Euvolemic: Water restriction, loop diuretics, or ADH antagonists (e.g., tolvaptan).
• Hypervolemic: Fluid and sodium restriction, use of loop diuretics.

Hypernatremia

• General Approach: Replace free water deficit.
• Hypovolemic: Initial fluid resuscitation with normal saline followed by free water.
• Euvolemic: Use of desmopressin for central DI; thiazides for nephrogenic DI.
• Hypervolemic: Utilize loop diuretics and possibly thiazides to manage sodium and water overload.

Conclusion

• Emphasis on understanding underlying pathophysiology and careful management of sodium disorders to avoid complications.