Which is an example of isovolemic hypernatremia?

Which is an example of isovolemic hypernatremia?

• A. Seawater ingestion
• B. Cushings
• C. Diabetes insipidus
• D. Lack of water intake

Answer: (C)

Isovolemic hypernatremia occurs when free water is lost or not replaced, so serum sodium rises while extracellular fluid volume stays essentially normal. The body loses water but does not lose sodium in the same proportion, so the overall volume remains euvolemic. Diabetes insipidus fits this pattern because lack of ADH effect (central DI) or kidney insensitivity to ADH (nephrogenic DI) causes large amounts of dilute urine and free water loss. As water is lost, serum sodium climbs, but the extracellular fluid volume does not become significantly depleted or expanded, since sodium balance is preserved and thirst/polydipsia can help maintain volume. Seawater ingestion, Cushings, and lack of water intake involve different volume changes. Ingesting seawater adds salt and water, but the net effect is usually hypervolemia with hypernatremia due to excess sodium. Cushings causes sodium and water retention, also hypervolemic. Lack of water intake tends toward hypovolemia from inadequate total body water, not isovolemic hypernatremia.

Isovolemic hypernatremia occurs when free water is lost or not replaced, so serum sodium rises while extracellular fluid volume stays essentially normal. The body loses water but does not lose sodium in the same proportion, so the overall volume remains euvolemic. Diabetes insipidus fits this pattern because lack of ADH effect (central DI) or kidney insensitivity to ADH (nephrogenic DI) causes large amounts of dilute urine and free water loss. As water is lost, serum sodium climbs, but the extracellular fluid volume does not become significantly depleted or expanded, since sodium balance is preserved and thirst/polydipsia can help maintain volume.

Seawater ingestion, Cushings, and lack of water intake involve different volume changes. Ingesting seawater adds salt and water, but the net effect is usually hypervolemia with hypernatremia due to excess sodium. Cushings causes sodium and water retention, also hypervolemic. Lack of water intake tends toward hypovolemia from inadequate total body water, not isovolemic hypernatremia.