II. Pathophysiology
- Hypovolemia with Decreased Total Body Sodium (but extracellular Hypernatremia)
III. Causes: Renal Sodium Loss (impaired renal concentrating ability)
- Findings
- Urine Osmolality 300-600 mOsm/kg
- Urine Sodium >20 meq/liter
- Causes (Hypotonic Polyuria)
- Diuretics
- Interstitial Nephritis (Nephrogenic DIabetes)
- High urine flow states
- Severe protein Malnutrition
- Hypokalemia
- Hypercalcemia
- Osmotic diuresis (usually results in Hyponatremia)
- Hyperosmolar nonketotic coma
- Glycosuria (excess Urine Glucose)
- Mannitol
- Postobstructive diuresis
- Enteral Feedings
- Non-oliguric Acute Tubular Necrosis (ATN) - recovery phase
IV. Causes: Extra-renal Sodium Loss
- Findings
- Urine Osmolality >600-800 mOsm/kg water
- Urine Sodium <10-20 meq/liter
- Causes
- Gastrointestinal losses
- Vomiting
- Osmotic Diarrhea
- Nasogastric suction
- Respiratory losses
- Skin losses
- Heat Illness
- Adrenal Insufficiency
- Gastrointestinal losses
V. Management
- Reverse underlying causes (especially renal underlying causes)
-
Sodium correction (moderate to severe Hypernatremia)
- Calculate Free Water Deficit
- Replace Free Water Deficit with D5W over 48 hours
- Chronic Hypernatremia (>48 hours) should be replaced slowly (esp. in under age 30-40 years)
- Limit Serum Sodium reduction to 12 mEq/L per day
- Correction rate
- Acute: 1 mEq/hour
- Chronic: 0.5 mEq/hour (do not decrease Sodium >8-10 mEq in 24 hours)
- Delivery
- Enteral water sources are preferred (e.g. Feeding Tube)
- D5W is an alternative (avoid 1/2NS due to risk of volume overload)
- Monitor Electrolytes closely while administering D5W
- Serum Sodium
- Serum Osmolality
- Do not decrease faster than 1-2 mOsm/kg water/hour
- Initial: Restore extracellular fluid volume to correct Hypotension
- Administer Normal Saline (0.9%)
- Next: Correct Serum Sodium
- Administer free water as above
- Treat underlying renal causes
- Losses from fever or Mechanical Ventilation
- Treat underlying renal causes
- Central Diabetes Insipidus
- Replace ADH (Desmopressin)
- Nephrogenic Diabetes Insipidus
- Treat primary problem (e.g. withdraw offending agent)
- Central Diabetes Insipidus