Water Balance

Water Balance

Water Balance

Sodium and Water balance:

Volume First!

• Serum sodium level usually reflect water balance.

• The body will normally adjust ADH and Aldosterone to protect intravascular volume, even at the expense of osmolality (reflected by serum sodium).

• When you see an abnormality of serum sodium, look at volume status and ask what ADH and Aldosterone are (or should be) doing?

Water Disorders:

• Diabetes Insipidus
• Inability of kidneys to concentrate urine appropriately
• • Due to an Anti-Diuretic Hormone (ADH) problem.
• ADH Deficiency- Central D.I.
• ADH Resistance- Nephrogenic D.I.
• • Symptoms
• – Polyuria and Polydipsia (ie: nocturnal urinating / drinking)
• • Recurrent episodes of dehydration whenever PO intake limited
• • Craving for water or Ice water.
• • Lab
• • Blood: High Sodium and High osmolality
• • Urine: Low Osmolality and variable sodium 
• • Other electrolytes and pH are normal 
• Diagnosis
• • Diabetes Insipidus
  • • High Urine output with Low Urine Osmolality and High Serum Osmolality.
  • Water Deprivation test:
  • – Restrict fluids:
  • Minimal or no change in Urine Output
  • Minimal increase in Urine Osmolality
  • inc Serum Osmolality
  • inc Serum Na+
  • • Serum ADH
  • – Low = Central DI
  • – High = Nephrogenic DI
• SIADH: Syndrome of Inappropriate Anti-diuretic Hormone
• • Inappropriately High ADH levels
• – Blood: Low sodium and Low Osmolality
• – Urine: Low volume and High osmolality
• Normal (or mild increase) in volume status
• Primary Polydipsia
• Excessive Water Intake >>> ability of kidney to excrete
• – Blood: Low sodium and Low osmolality 
• – Urine: High volume and Low osmolality
• Seen mostly with alcoholism (beer) and psychiatric disorders.

Summary

CAPACITY OF KIDNEY TO GET RID OF WATER = 16 ml/min