II. Pathophysiology
- Decreased Total Body Water (TBW)
- Normal Total Body Sodium
- Normal Extracellular Fluid
III. Causes: Extra-renal Water Loss
- Findings
- Urine Osmolality increased
- Causes
- Skin losses
- Respiratory losses
- Iatrogenic Example of excess Sodium administration
- Febrile, tachypneic patient
- Hypotonic insensible loss replaced with 0.9% saline
- Rhabdomyolysis
- Damaged cells extract water from ECF
- Sickle Cell Anemia
IV. Causes: Renal Water Loss
-
Central Diabetes Insipidus
- Secondary to CNS injury
- Desmopressin results in return of urinary concentrating function
-
Nephrogenic Diabetes Insipidus
- Desmopressin does not result in improvement of urinary concentrating function
- Results from nephrotoxic medications (e.g. Amphotericin, Lithium, Demeclocycline)
V. Management
- Mild to moderate Hypernatremia
- Increase free water intake
-
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)
- Monitor Electrolytes closely while administering D5W
- Serum Sodium
- Serum Osmolality
- Do not decrease faster than 1-2 mOsm/kg water/hour
- Delivery
- Enteral water sources are preferred (e.g. Feeding Tube)
- D5W is an alternative (avoid 1/2NS due to risk of volume overload)