• Surgical difficulty [ Time Frame: Intraoperatively ]
  Score of the difficulty of the surgery by the surgeon through the Thyroidectomy Difficulty Scale.
• Intraoperative hemorrhage [ Time Frame: Intraoperatively ]
  Amount of blood lost during the thyroidectomy in dL.
• Surgical time. [ Time Frame: Intraoperatively. ]
  Time from surgical incision to skin closure in minutes.
• Intraoperative neuromonitoring. [ Time Frame: Intraoperatively. ]
  Rate of patients with loss of electromyographic signal during intraoperative neuromonitoring.
• Postoperative Long of Stay [ Time Frame: 30 days after surgery ]
  Days to hospital discharge after surgery.
• Readmissions [ Time Frame: 30 days after surgery. ]
  Rate of readmissions.
• Permanent complications [ Time Frame: 180 days after surgery ]
  Rate of patients with permanent complications, including hypoparathyroidism or recurrent laryngeal nerve injury.
• Adverse events [ Time Frame: 180 days after surgery ]
  Number of patients with an adverse event after administration of Lugol solution.

Currently, both the American Thyroid Association and the European Thyroid Association recommend the use of Lugol Solution (LS) in the preparation of patients undergoing thyroidectomy for Graves' disease (GD), but their recommendations are based on a low level of evidence. This means that its use is not generalized among the different endocrine surgery units.

Methods:

Study population: 270 patients (135 patients in each arms) undergoing total thyroidectomy (TT) due to GD in Spanish hospitals, which perform a minimum of 100 thyroidectomies a year, at least 10 of them for GD.

Variables:

Preoperative variables

• Demographic variables: birthdate, gender and ethnicity.
• Drugs allergies. Allergy to iodine.
• Personal history and usual treatment.
• Aspects related to the GD: date of diagnosis, use of AT drugs and/or radioiodine, existence of ophthalmopathy, existence of cervical compression symptoms and indication of surgery.
• Physical exploration: body mass index, pulse at rest and blood pressure and cervical palpation.
• Laboratory tests: hematocrit, leukocytes, neutrophils, platelets, international normalized ratio(INR), creatinine, potassium, total calcium, albumin, total proteins, parathormone (PTH), 25-hydroxide-vitamin D, free T4 and / or free T3, TSH, thyroid stimulating immunoglobulin (TSI).
• Classification of the anesthetic risk of ASA.
• Cervical ultrasound: existence of thyroid nodules and volume of the thyroid.
• Mobility of the vocal cords evaluated by laryngoscopy.
• Compliance with assigned treatment: the patient assigned to the LS arm must have consumed at least 80% of the total dose indicated.

Intraoperative variables

• Surgical time.
• Antibiotic prophylaxis
• Intraoperative hemorrhage.
• Thyroidectomy Difficulty Scale.
• Loss of electromyographic signal during neural intraoperative monitorization.
• Accidental parathyroidectomy.
• Section or obvious lesion of the recurrent laryngeal nerve.
• Trachea or esophagus perforation.
• Weight of the gland.
• Electrosurgical hemostasis system used during the intervention.
• Maneuvers used to check hemostasis.
• Hemostats used during the intervention.
• Use of drainage.
• Definitive surgical technique: TT, unilateral or bilateral subtotal thyroidectomy or hemithyroidectomy.

Postoperative variables

• Early complications: hypoparathyroidism, paralysis of the recurrent laryngeal nerve, postoperative hematoma, surgical site infection or death.
• Debit for surgical drains.
• Postoperative hospital long of stay.
• Anatomopathological variables: histological diagnosis compatible with GD and existence of parathyroid glands in the surgical specimen.
• Long-term complications: hypocalcemia and/or permanent vocal cord paralysis longer than 6 months

• Experimental: Preoperative Lugol Solution preparation
  Patients will receive Lugol Solution preparation for 10 days before thyroidectomy
  Intervention: Drug: Lugols Strong Iodine
• No Intervention: No preparation
  Patients will not receive preparation before thyroidectomy

Inclusion Criteria:

Patients who meet all of the following criteria will be eligible:

• The age of the patient must be over 18 years of age.
• The patient or his / her tutor, in cases where this is the case, has the capacity to understand the study and agrees to participate in it, by signing the corresponding informed consent document.
• Patients who have been diagnosed with GD, defined as the existence of hyperthyroidism (TSH < lower limit of laboratory normality associated with TSI > upper limit of laboratory normality) that present ultrasonographic data (diffuse vascularization increase) and / or scintigraphy (diffuse uptake of the radioisotope) compatible with GD.
• Euthyroid patients (free T4 and / or free T3 within the normal range of the laboratory) at the time of randomization, and under treatment with AT drugs (propylthiouracil, carbimazole or methimazole).
• The patient must be proposed for total thyroidectomy, using a transcervical approach.

Exclusion Criteria:

The participant can not participate in the study if he / she presents any of the following circumstances:

• Prior cervicotomy by surgical intervention on the thyroid or parathyroid gland.
• Associated hyperparathyroidism that requires associating a parathyroidectomy in the same surgical act.
• Associated thyroid cancer that requires adding a lymph node dissection of the central or lateral compartment in the same surgical time.
• Iodine allergy.
• Consumption of lithium or amiodarone between randomization and administration of LS.
• Patients with category IV of the anesthetic risk classification of the American Society of Anesthesiologists (ASA).
• Women who breastfeed during the administration of the LS or in the month after it.
• Preoperative palsy of a vocal cord verified by laryngoscopy.
• Surgery performed by training specialists, or by staff not specifically dedicated to endocrine surgery.
• Surgery not performed under general anesthesia.
• Endoscopic surgery, video assisted or by remote approach.
• Surgery performed in out-patient settings.
• Current drug consumption or alcohol abuse that could interfere with meeting the study requirements.
• Participation in any other trial with medications in the month prior to randomization.