Correction of hypervolaemic hypernatraemia by inducing negative Na+ and K+ balance in excess of negative water balance: a new quantitative approach.

BACKGROUND: Hypervolemic hypernatremia is caused by an increase in total exchangeable Na(+) and K(+) in excess of an increment in total body H(2)O (TBW). Unlike patients with hypovolemic or euvolemic hypernatremia, treatment needs to be targeted at correcting not only the elevated plasma Na(+) concentration, but also there is an additional requirement to achieve negative H(2)O balance to correct the increment in TBW.

METHODS: Correction of hypervolemic hypernatremia can be attained by ensuring that the negative Na(+) and K(+) balance exceeds the negative H(2)O balance. These seemingly conflicting therapeutic goals are typically approached by administering intravenous 5% Dextrose (IV D5W) and furosemide.

RESULTS: Currently, there is no quantitative approach to predicting the volume of IV D5W (V(IVF)) that needs to be administered that satisfies these requirements. Therefore, based on the principle of mass balance and the empirical relationship between exchangeable Na(+), K(+), TBW, and the plasma Na(+) concentration, we have derived a new equation which calculates the volume of IV D5W (V(IVF)) needed to lower the plasma Na(+) concentration ([Na(+)](p1)) to a targeted level ([Na(+)](p2)) by achieving the desired amount of negative H(2)O balance (V(MB)): V(IVF) = {([Na(+)](p1) + 23.8) (TBW(1)) - ([Na(+)](p2) + 23.8)(TBW(1) + V(MB)) + 1.03 ([E](input) x V(input) - [E](output) x V(output) - [E](urine) (V(input) - V(output) - V(MB)))}/1.03 x [E](urine) where [E] = [Na(+) + K(+)] and input and output refer to non-infusate and non-renal input and output respectively.

CONCLUSION: This new formula is the first quantitative approach for correcting hypervolemic hypernatremia by achieving negative Na(+) and K(+) balance in excess of negative H(2)O balance.