Studies have attempted to control pain and increase patients' recovery satisfaction following many kinds of operations by using as small an opioid analgesic dose as possible and adding a nonopioid analgesic to reduce the side effects of narcotic analgesics. Among nonopioid analgesics, lidocaine and magnesium are drawing attention, having been shown to be helpful in controlling postoperative pain by lowering pain hypersensitivity to surgical stimuli. Lidocaine acts as an antagonist of the N-methyl-D-aspartate (NMDA) receptor. An intraoperative intravenous injection of lidocaine has been reported to improve postoperative pain control by reducing postoperative pain and opioid consumption. Another report showed that an intraoperative intravenous injection of lidocaine improved the quality of postoperative functional recovery after general anesthesia in a laparoscopic cholecystectomy patient. In addition, a review article on the effect of intraoperative intravenous injection of magnesium found it to be an effective analgesic that may be added to conventional opioid-based therapy because it generally reduces opioid consumption, decreases pain assessment for 24 hours after surgery, and lacks severe side effects in relation to magnesium administration. However, there has been insufficient research comparing the intraoperative intravenous injection of lidocaine or magnesium in terms of which is more helpful for general functional recovery and decreased postoperative pain. Recently, the scope of research on anesthesia has come to embrace postanesthetic recovery; to help patients return to daily life, the research trend is now shifting from the improvement or resolution of a specific symptom to the measurement of general recovery. Postoperative recovery is a complicated process related to such catamnestic factors as physiological end-points, the incidence of adverse events, and changes in psychological status. A widely used method to measure postoperative recovery is the Quality of Recovery 40 (QoR-40) survey. The QoR-40 includes a total of 40 questions that may be divided into five sub-categories: emotional state, physical comfort, psychological support, physical independence, and pain. The respondent answers each question on a 5-point scale, with one being worst and five being best. The QoR-40 takes 6.3 minutes on average to complete and is known to have good test-retest reliability, internal consistency, and split-half reliability. With respect to anesthetic recovery, the QoR-40 has been used in various studies to investigate how the surgery type, anesthesia method, administration of an additional drug, and gender affect anesthesia and surgery. The validity of the QoR-40 for research purposes has already been established.

Therefore, in this study, we investigated the intraoperative intravenous injection of lidocaine and the intravenous injection of magnesium to compare these drugs' helpfulness in the functional recovery of thyroidectomy patients after general anesthesia.

Inclusion Criteria:

• Patients aged between 20 and 65 who have undergone thyroidectomy due to thyroid cancer and of American Society of Anesthesiologists (ASA) Physical Status Class 1 or Class 2

Exclusion Criteria:

• Patients experiencing pain for any cause or taking an analgesic
• Pregnant patients
• Patients with severe heart, kidney, or liver disease
• Patients with a psychiatric or neurological disorder
• Patients with a contraindication or allergic response to lidocaine
• Patients with a contraindication or allergic response to magnesium