SIADH vs Diabetes Insipidus (DI): Key Differences and Understanding ADH

Introduction

• Presenter: Sarah, RN from register nurse rn.com
• Objective: Explain differences between Syndrome of Inappropriate Antidiuretic Hormone (SIADH) and Diabetes Insipidus (DI) focusing on the role of Antidiuretic Hormone (ADH)
• Purpose: Clarify concepts for NCLEX and nursing exams
• Recommendation: Visit the website for a quiz to test knowledge

Role of Antidiuretic Hormone (ADH)

• Also Known As: Vasopressin
• Function:
  • Regulates water in the body
  • Constricts blood vessels
  • Works with kidneys: Causes renal tubules to retain water
• Brain Areas Involved:
  • Hypothalamus: Produces ADH
  • Posterior Pituitary Gland: Stores and secretes ADH

SIADH vs DI Overview

• SIADH: Increased ADH
• DI: Decreased ADH
• Mnemonic: SIADH contains 'I' which stands for "increase" in ADH

Causes

SIADH

• Primary Causes:
  • Lung cancer, particularly small cell lung cancer
  • Damage to hypothalamus/posterior pituitary
  • Infections (e.g., pneumonia, meningitis)
  • Medications (e.g., Chlorpropamide)

DI

• Primary Causes:
  • Kidney issues where kidneys are not responsive
  • Medication-induced (e.g., Declomycin)
  • Pregnancy (gestational DI)
  • Brain trauma affecting ADH production

Signs and Symptoms

SIADH

• Water retention leading to fluid overload
• Manifestations:
  • Edema
  • Weight gain
  • Hypertension
  • Tachycardia
  • Hyponatremia due to dilution
  • Confusion, risk of seizures
  • Low urine output, concentrated urine

DI

• Excessive urination and dehydration
• Manifestations:
  • Polyuria (4-24L/day)
  • Polydipsia (excessive thirst)
  • Dehydrated appearance (dry skin, mucous membranes)
  • Hypotension
  • Diluted urine, low specific gravity
  • Hypernatremia due to fluid loss

Nursing Interventions

• General:
  • Monitor daily weights
  • Strict intake and output measurement
  • Ensure patient safety (risk of falls/confusion)

SIADH-Specific

• Implement fluid restriction
• Monitor for fluid overload

DI-Specific

• Avoid diuretic foods (e.g., caffeine, watermelon)
• Monitor for dehydration

Medical Treatment

SIADH

• Loop Diuretics (e.g., Lasix):
  • Promote diuresis, watch for hypokalemia
• Hypertonic IV Solution:
  • Used with caution to draw fluid out of cells
  • Risk of exacerbating fluid overload
• Declomycin: Inhibits ADH

DI

• Chlorpropamide (Diabinese):
  • Increases ADH, monitor for hypoglycemia
  • Photosensitivity precautions
• Desmopressin:
  • Synthetic vasopressin to replace ADH
  • Monitor for hyponatremia

Conclusion

• Understanding the role and regulation of ADH is crucial to managing SIADH and DI
• Visit register nurse rn.com for additional resources and quizzes