What is the most important action for a nurse to take for a preschool-aged child experiencing polyuria and low blood pressure?

The most important action for a nurse to take in this situation is to start an intravenous infusion of normal saline. Polyuria in a preschool-aged child, combined with low blood pressure, suggests that the child may be experiencing dehydration or fluid loss that requires immediate attention.

Administering normal saline IV provides a rapid rehydration solution that can help restore the child's blood volume and improve blood pressure. This is particularly crucial in children, as they are more vulnerable to the effects of dehydration than adults. Expanding vascular volume through IV fluids can improve perfusion to vital organs, stabilize blood pressure, and prevent further complications.

While inserting an indwelling urinary catheter may assist in monitoring the child’s output more accurately, it does not address the immediate problem of low blood pressure and dehydration. Documenting the child's findings and vital signs is important for record-keeping and clinical assessment, but it does not provide the necessary intervention to resolve the child's potentially critical condition. Reviewing serum electrolyte results is relevant for understanding the child's overall status and guiding further treatment, but it is not an immediate action. Starting IV fluids takes priority to manage the acute symptoms of polyuria and hypotension.