Final answer:
The laboratory result indicating an effective treatment regimen for hypotonic dehydration would be increased blood sodium levels, as this reflects a correction in the electrolyte imbalance and restoration of osmotic balance.
Step-by-step explanation:
A nurse caring for a child with hypotonic dehydration who is receiving an oral rehydration solution would look for specific changes in lab results that indicate successful treatment. Hypotonic dehydration is a condition where the level of salt, or sodium, in the blood is too low. Given that an effective treatment should aim to correct this imbalance, the laboratory result indicating an effective treatment regimen would be increased blood sodium levels (c). This means that sodium in the bloodstream is being replenished, and the osmotic balance is being restored, diminishing the risk of cells swelling from excessive water intake. It is important to monitor for changes in blood pressure and other solute levels such as potassium and glucose, to ensure overall electrolyte and fluid balance is being maintained.