Formula for Hyponatremia and Hypernatremia

HyponatremiaEstimated Serum Osmolality Formula:

Estimated Serum Osmolality = 2 × Na (mEq/L) + (Glucose (mg/dL) / 18) + (BUN (mg/dL) / 2.8)

Hyperglycemia Adjustment in Hyponatremia:

Corrected Na = Measured Na + [(Current Glucose (mg/dL) - 100) / 100] × Δ

Δ (Delta) varies: Use 1.6 for glucose <400 mg/dL, and 2.4 for glucose ≥400 mg/dL.

IV Fluid Administration for HyponatremiaSodium Deficit Calculation:

Sodium Deficit (mEq) = (Desired Na - Actual Na) × TBW

Total Body Water (TBW) = weight (kg) × 0.6 for men or 0.5 for women.

HypernatremiaWater Deficit Calculation for Hypernatremia Correction:

Water Deficit (L) = [(Serum Na / 140) - 1] × weight (kg) × Body Water Constant

Note: Body Water Constant is 0.6 for males and 0.5 for females.