What is the function of Lugol's (potassium iodide) iodine preoperatively?

Function of Lugol's Iodine Preoperatively

Preoperative Lugol's iodine solution is primarily used to reduce thyroid vascularity and hormone release before thyroid surgery, particularly in patients with Graves' disease or hyperthyroidism, resulting in decreased intraoperative bleeding and improved surgical outcomes.

Mechanism of Action

Lugol's solution contains potassium iodide and iodine in water, which works through several mechanisms:

1. Reduction in thyroid vascularity:

   • Decreases blood flow to the thyroid gland
   • Reduces the risk of intraoperative bleeding 1
   • Makes the thyroid gland firmer and less friable during surgery

2. Blockade of thyroid hormone release:

   • Saturates the thyroid gland with non-radioactive iodine
   • Inhibits thyroid hormone synthesis (Wolff-Chaikoff effect)
   • Rapidly reduces circulating thyroid hormone levels 2

Clinical Evidence

Research demonstrates significant benefits of preoperative Lugol's solution:

• A randomized controlled trial showed that Lugol's solution treatment resulted in a 7.40-fold decrease in intraoperative blood loss during thyroidectomy 1
• Another study demonstrated that after 10 days of treatment with Lugol's solution (combined with dexamethasone and beta-blockers), free T4 and free T3 levels were significantly reduced, and all patients became clinically euthyroid 2
• However, a recent 2024 randomized clinical trial challenges some of these findings, showing that while Lugol's solution significantly reduced FT3 and FT4 levels, it did not decrease intraoperative/postoperative blood loss or thyroid vascularization 3

Clinical Applications

Lugol's solution is most commonly used in:

1. Preoperative preparation for thyroidectomy in Graves' disease:

   • Typically administered 7-10 days before surgery
   • Helps achieve euthyroid state before surgery
   • Reduces risk of thyroid storm during surgery

2. Management of thyrotoxic crisis/thyroid storm:

   • Used as part of emergency treatment protocol
   • Rapidly blocks release of thyroid hormones

3. Rescue treatment in uncontrolled hyperthyroidism:

   • When antithyroid drugs cause adverse effects (agranulocytosis, hepatotoxicity)
   • When patients have poor adherence to medication 4

Dosing and Administration

• Typical protocol: 2-3 drops of Lugol's solution (8 mg iodide per drop) three times daily for 7-10 days before surgery
• Should be administered as soon as possible before surgery for maximum effect
• Often combined with beta-blockers and sometimes corticosteroids for optimal control

Potential Complications and Cautions

1. Side effects:

   • Allergic reactions (rash, swelling) in approximately 15% of patients 4
   • Metallic taste, nausea, vomiting
   • Rarely can cause chemical esophagitis

2. Paradoxical effects:

   • Can rarely cause painless thyroiditis with initial thyrotoxicosis followed by hypothyroidism 5
   • Prolonged use is not recommended due to potential adverse effects

3. Contraindications:

   • Known iodine allergy
   • Pregnancy (unless specifically indicated)
   • Caution in patients with renal insufficiency

Clinical Pearls

• Lugol's solution should not be used long-term for non-surgical indications
• The solution should be diluted in water or juice to improve palatability
• Maximum effect on thyroid hormone levels typically occurs within 10-14 days
• Adrenal function should be monitored if combined with corticosteroids, as secondary adrenal insufficiency may occur 2
• Patients should be monitored for signs of iodine-induced hyperthyroidism, especially in iodine-deficient areas 6

While recent evidence shows mixed results regarding its effect on intraoperative bleeding, Lugol's solution remains a valuable tool in the preoperative management of hyperthyroid patients, particularly when rapid control of thyroid hormone levels is needed before surgery.