Hyponatremia

Patient's baseline Na ***. Duration likely ***. Patient appears to be hypo/hyper-volemic*** given physical exam***. Patient's urine output ***. Patient is on *** medications/IV infusions that could result in hyponatremia.

Serum evaluation: Chem 10, osms, glucose, Corrected Na = measured Na + [(serum glucose - 100)/100]*1.6
Consider total protein and/or lipids for pseudohyponatremia
Consider uric acid, TSH, AM cortisol
Urine studies: Urine lytes (Na, K), uUrea, uCr, uOsms, urine volume
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Determine if ADH is being secreted:
- ADH present: uOsm > 150 (300-500) mosm, uNa <20-25
- ADH absent: uOsm <100, uNa >20-40
- Unsure: give small isotonic fluid challenge and recheck sNa

If ADH present, determine if ADH secretion is appropriate:
- Appropriate: Volume depletion (bleeding, GI and Renal fluid loss), or decreased effective circulating volume (CHF, cirrhosis, nephrotic syndrome)
- Inappropriate: SIADH, pulmonary disease (pneumona, PE, lung Ca), pain, stress, nausea, spinal cord injury/CNS pathology, medications (SSRI, diuretics, ectasy, chemotherapy)
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Determine patient's capacity to excrete free water.
- Ensure adequate osmole intake and generation to allow for free water intake (good intake, r/o polydipsia), assess thyroid and adrenal function
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SIADH is a diagnosis of exclusion: 1) Patient is euvolemic, 2) Normal thyroid and adrenal function with no recent diuretic use, 3) Labs with uOsm >150, sOsm <275, uNa >20-40 with normal dietary salt intake. Often sUric acid <4, BUN <10, FeNA >2% or FeUrea >45%.
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Treatment:
- <48h: rapid correction appropriate.
- >72h:
HYPOVOLEMIC: volume expand with IVF

EUVOLEMIC:
- Asymptomatic: Use effective free water clearance:
ECFW= urine volume * [1- (uNa +K)/ sNa]
- If >0, is excreting free water. If free water intake is < output, hypoNa will correct
- If <0, actively reabsorbing free water and osm supplementation is required
--> Treatment = 500mg -2g PO 2-3x daily

HYPERVOLEMIC:
- Free water restrict (1-1.5L/day or less than calculated EFWC)
- Loop diuretics
- Emergent dialysis

RATE OF CORRECTION:
- Max rate 6-8/day
- If neuro sx present: 1-2/hr until sx resolve
- If hypertonic saline, check every 2-4h initially

IF OVERCORRECTION:
- IV D5 alone or with desmopressin
- Do not use demopressin in volume overload or self-induced water intox