What should be done if a sodium increase of 6 to 8 mmol/L is achieved?

Achieving a sodium increase of 6 to 8 mmol/L prompts a careful approach to fluid management. In this context, the appropriate action is to consider replacing free water. When sodium levels are elevated, especially in conditions like hypernatremia, it often indicates that the body is either losing free water or there is an imbalance in water intake.

After a controlled increase in sodium, it is crucial to ensure that the patient is adequately rehydrated to prevent complications that can arise from both too rapid changes in sodium levels and dehydration. By replacing free water, one helps to restore the body's fluid balance, allowing the sodium concentration to gradually normalize without causing cellular edema from too rapid correction.

The other responses do not directly address the need for careful fluid management after a significant increase in serum sodium. Starting additional hypertonic saline could further increase sodium levels, which is counterproductive. Stopping all fluid intake is not appropriate in cases where free water needs to be replaced, and administering calcium supplements does not relate to the management of sodium levels.