SIADH vs. DI Key Differences

Overview

This lecture explains the key differences between SIADH (Syndrome of Inappropriate Antidiuretic Hormone) and DI (Diabetes Insipidus), focusing on pathophysiology, lab findings, clinical signs, and nursing interventions.

SIADH: Key Features and Management

• SIADH means excessive ADH causes the body to retain water, resulting in fluid overload.
• Memory trick: "SI soaked inside"—body is swollen with fluid.
• Key lab findings: low serum osmolality and low sodium (hyponatremia, <135), high urine specific gravity (>1.030).
• Urine output is low; urine is thick, sticky, and concentrated.
• Major symptoms: headache, confusion, agitation (early hyponatremia signs), seizures, and increased blood pressure.
• Nursing interventions: fluid restriction, monitor for seizures, add sodium (3% saline if needed), monitor strict input/output, and daily weights.

Diabetes Insipidus (DI): Key Features and Management

• DI means lack of ADH, leading to the body losing large amounts of water and dehydration.
• Memory trick: "DI dry inside"—body is dehydrated.
• Key lab findings: high serum osmolality and high sodium (hypernatremia, >145), low urine specific gravity (<1.005).
• Urine output is very high (up to 20L/day); urine is diluted and clear.
• Major symptoms: increased thirst, dry mucous membranes, poor skin turgor, low blood pressure, and weight loss.
• Treatment: desmopressin (synthetic ADH), monitor sodium closely to avoid hyponatremia.

Causes: SIADH vs. DI

• Both can be caused by brain damage (tumors, trauma, surgery) affecting the posterior pituitary where ADH is produced.
• SIADH specific cause: also associated with small cell lung cancer and some lung tumors secreting ADH.
• DI is often linked to direct brain/pituitary injury.

Nursing Care and NCLEX Tips

• Always monitor strict input/output and daily weights (not weekly) for both conditions.
• In SIADH, avoid adding fluids; restrict fluids and monitor for low sodium symptoms/seizures.
• In DI, expect high urine output, dehydration, and need for ADH replacement.
• Key NCLEX terms: low sodium and seizure precautions for SIADH; high sodium, high urine output, and increased thirst for DI.

Key Terms & Definitions

• ADH (Antidiuretic Hormone) — hormone from the posterior pituitary regulating body water by controlling kidney water reabsorption.
• SIADH — excessive ADH release, leading to water retention and dilutional hyponatremia.
• Diabetes Insipidus (DI) — insufficient ADH, leading to excessive water loss and dehydration.
• Osmolality — concentration of solutes in blood or urine; low in SIADH, high in DI.
• Specific Gravity — measure of urine concentration; high in SIADH, low in DI.
• Desmopressin — synthetic ADH used as treatment, especially in DI.

Action Items / Next Steps

• Review and memorize the "seven S’s" for SIADH and "seven D’s" for DI.
• Practice identifying NCLEX key terms for each condition.
• Study strict differences in lab values, symptoms, and nursing priorities for SIADH vs. DI.
• Complete assigned study guide and NCLEX-style practice questions from the membership portal.