II. Indications
III. Calculation: Normal Total Body Water (TBW)
IV. Calculation: Current Total Body Water (TBW)
 Current TBW = Normal TBW * (140 / sNa)
 Where 140 mEq/L is the normal Serum Sodium, and sNa is the current Serum Sodium
 Adjust measured Serum Sodium (sNa) for Hyperglycemia
V. Calculation: Free Water Deficit (Hypernatremia)
 Free Water Deficit (FWD in L) = (Normal TBW)  (Current TBW)
 Free Water Deficit (FWD in L) = (Normal TBW) * (sNa  140) / 140
 Free Water Deficit (FWD in L) = (Normal TBW) * (sNa/140  1)
 Where 140 mEq/L is the normal Serum Sodium, and sNa is the current Serum Sodium
 Adjustments to Total Body Water
 Decrease Total Body Water by 10% in Hypernatremia (multiply TBW * 0.9)
 Some equations use 0.5 * LbmKg as TBW for both men and women in Hypernatremia
VI. Calculation: Total Body Sodium Deficit or Water Excess (Hyponatremia)
 Excess Total Body Water (TBW)
 Excess TBW = Current TBW  Normal TBW

Sodium delivered by various crystalloid solutions (ivNa)
 Hypertonic Saline (3% NaCl): 513 meq/L
 Normal Saline or NS (0.9% NaCl): 154 meq/L
 Lactated Ringers or LR: 130 meq/L
 1/2 Normal Saline or 1/2NS (0.45% NaCl): 77 meq/L
 Total Body Sodium Deficit (NaDeficit)
 Sodium deficit (meq) = Normal TBW * (140  sNa)
 Where 140 mEq/L is the normal or desired Serum Sodium, and sNa is the current Serum Sodium
 IV Fluid rate (IVrate) to achieve a given rise in Sodium per hour (sNaChangePerH )
 IVrate = (1000 * sNaChangePerH * (TBWnorm + 1)) / (ivNa  sNa)
 where sNaChangePerH = Desired change per hour (typically <0.25 to <0.50 meq/h)
 where TBWnorm = Normal Total Body Water (see above for calculation)
 where ivNa = Sodium per Liter of IV fluid (see above)
 where sNa = Serum Sodium

Serum Sodium change per liter of IV fluids (sNaChangePerL)
 sNaChangePerL = (ivNa  sNa) / (TBWnorm + 1)
 where TBWnorm = Normal Total Body Water (see above for calculation)
 where ivNa = Sodium per Liter of IV fluid (see above)
 where sNa = Serum Sodium
VII. Resources
 Medscape Hyponatremia correction infusate rate
VIII. References
 Marino (2014) ICU Book, Wolters Kluwer, p. 65372
 Rose (1989) Clinical Physiology of Acid Base and Electrolytes, p. 81619
 Braun (2015) Am Fam Physician 91(5): 299307 [PubMed]