What action should a nurse take for a diabetic client with a blood glucose of 300 mg/dl?

Administering prescribed insulin is the appropriate action for a diabetic client with a blood glucose level of 300 mg/dl. When blood glucose levels are significantly elevated, such as in this case, it is crucial to lower the blood sugar to prevent acute complications associated with hyperglycemia, such as diabetic ketoacidosis (DKA) or hyperglycemic hyperosmolar state (HHS). Insulin is essential in facilitating the uptake of glucose by the cells, thus reducing the blood sugar level.

In addition, administering insulin helps stabilize the client’s condition and can prevent serious complications from occurring. It is vital to follow the healthcare provider's orders regarding the type and dosage of insulin to ensure effectiveness and safety.

The other options, while important in the broader context of diabetic care, do not address the immediate need to lower the blood glucose level. Encouraging dietary restrictions, monitoring closely, or calling for immediate help may be relevant actions under certain circumstances, but they are not as critical as ensuring that the client receives insulin in this scenario.