Dysnatremias are challenging problems in patients undergoing renal replacement therapy. The ability to manipulate sodium concentration in the dialysate or replacement solutions is limited.
Below are simple formulas developed by Drs. Tinawi and Bastani. They help determine the rate of hypotonic or hypertonic solutions needed to mitigate rapid correction of dysnatremias. These formulas can be used readily by the clinician at bedside.
Formula 1: Change in serum sodium at the end of hemodialysis session
Formula 2: Blood flow rate (Qb) needed for a slow rise in serum sodium
Formula 3: Volume of D5W needed to slow down the rate of serum sodium rise
Formula 4: Volume of 3% saline needed to slow down rapid the rate of serum sodium decline
Formula 5: Volume of D5W needed to slow the rate of serum sodium rise in CVVH
Formula 6: Volume of D5W needed to slow the rate of serum sodium rise in CVVHDF
Formula 7: Increase in serum na after 1 hour of CRRT
Formula 8: Volume of 3% saline to slow the decline in serum sodium in CVVHDF
Formula 9: Decrease in serum sodium after 1 hour of CRRT
Tinawi, Mohammad, and Bahar Bastani. “A mathematical approach to severe hyponatremia and hypernatremia in renal replacement therapies.” Seminars in Dialysis. 2020.