In the case of desalination from renal salt loss

• Usually occurs since ~Day 3 of DDAVP-HTS treatment
  • 
    • (↑ renal Na excretion gradually following ↑ Na intake, usually peak at around day 3)
• Often with ↑Urine [Na+K] leading to ↑UO despite UOsm remains high
  1. E.g. UO >150ml/h & Urine [Na+K] >150mmol/L
• Can compensate this loss with ↑HTS infusion rate
  1. Needed rate of compensation can be calculated by Edelman equation
     • Can use Dr Stern's calculator to get the desire rate directly (= actual rateto prescribe)
       • otherwise you can use the calculator attached below to obtain the rate to compensate renal loss only
         • (if a negative number is generated it means compensation is unnecessary)

  2. CAUTION: this approach is safe ONLY IF UO & Urine [Na+K] relatively static over the past 6 hours

  3. as you raise Na input rate, Urine [Na+K] may further increase gradually so calculation may need to be repeated to adjust  HTS rate accordingly.

Calculator by the legend nephrologist (and expert in hypoNa) Dr Richard Sterns:

Calculator | Mysite (richardsternsmd.com) 

Junior members are suggested to discuss with on duty consultant before increasing HTS rate drastically (e.g. more than double of the current rate & >60ml/h)

Calculator for the HTS / NaCl needed to compensate renal loss

NB: I created this calculator before Dr Sterns published his site. This calculator may also be particularly useful for the transition from HTS to NaCl tab (which isn't incorporated in Dr Sterns' calculator), and before DDAVP effect completely wears off after stopping its regular administration.

Reference: Chen S, Shey J, Chiaramonte R. Ratio Profile: Physiologic Approach to Estimating Appropriate Intravenous Fluid Rate to Manage Hyponatremia in the Syndrome of Inappropriate Antidiuresis. Kidney360. 2022 Dec;3(12):2183.