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Isovolemic HypernatremiaAka: Hypernatremia with Normal Total Body Sodium

Pathophysiology
1. Decreased Total Body Water (TBW)
2. Normal Total Body Sodium
3. Normal Extracellular Fluid
Extra-renal Water Loss
1. Findings
  1. Urine Osmolality increased
2. Causes
  1. Skin loss
  2. Pulmonary loss
  3. Iatrogenic Example of excess sodium administration
    1. Febrile, tachypneic patient
    2. Hypotonic insensible loss replaced with 0.9% saline
  4. Rhabdomyolysis
    1. Damaged cells extract water from ECF
Renal Water Loss
1. Central Diabetes Insipidus
2. Nephrogenic Diabetes Insipidus
Management
1. Calculate Free Water Deficit
2. Replace Free Water Deficit with D5W over 48 hours
3. Monitor electrolytes closely while administering D5W
  1. Serum Sodium
  2. Serum Osmolality
    1. Do not decrease faster than 1-2 mOsm/kg water/hour
4. Treat Diabetes Insipidus specifically
  1. Central Diabetes Insipidus: Replace ADH
  2. Nephrogenic Diabetes Insipidus: Treat primary problem

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 6/1/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.