What is the most important preoperative nursing intervention for a patient undergoing subtotal thyroidectomy for a large multinodular goiter causing tracheal deviation and stridor?

The patient, Abena, has a large multinodular goiter causing tracheal deviation and stridor, and is scheduled for a subtotal thyroidectomy. The question asks for the most important preoperative nursing intervention.

• A. Teach head support after surgery: This is a crucial postoperative teaching point to prevent strain on the surgical site and protect the airway.
• B. Administer Lugol's iodine as prescribed: Lugol's iodine (potassium iodide) is often administered preoperatively for thyroidectomy. Its purpose is to decrease the vascularity and size of the thyroid gland, which reduces the risk of hemorrhage during surgery and can make the procedure safer, especially with a large goiter. This is a direct preoperative intervention aimed at preparing the gland for surgery.
• C. Place a tracheostomy tray at the bedside: A tracheostomy tray is kept at the bedside postoperatively as a precaution in case of airway obstruction due to edema or hematoma, which are potential complications of thyroidectomy.
• D. Monitor for hypocalcemia: Hypocalcemia is a potential complication postoperatively if the parathyroid glands are inadvertently damaged or removed during surgery. Monitoring for this is a postoperative intervention.

Given that the question asks for the most important preoperative intervention, administering Lugol's iodine directly addresses the preparation of the thyroid gland for surgery, reducing surgical risks associated with a large, vascular goiter.

The final answer is $\boxed{\text{B}}$.