During thyroid surgery, Intraoperative Neuromonitoring (IONM) plays a crucial role in preventing serious complications such as bilateral vocal cord paralysis. It achieves this by detecting damage to the recurrent laryngeal nerve (RLN) and predicting the RLN's functional status. The utilization of Nerve Integrity Monitoring tubes (NIM tubes) is on the rise for effective IONM. As IONM relies on observing electromyographic (EMG) responses to direct electrical nerve stimulation, the routine use of neuromuscular blocking agents (NMBAs) in general anesthesia can impact the interpretation of IONM results and potentially reduce sensitivity to nerve responses to stimulation. However, the use of NMBAs is essential for ensuring smooth endotracheal intubation in patients undergoing general anesthesia. Numerous studies suggest that NMBA usage provides superior intubation conditions and reduces vocal cord complications compared to scenarios without NMBA.

Various regimens for neuromuscular blockade methods are employed during IONM in thyroid surgery, ranging from not using NMBAs at all to using a full dose of NMBA for intubation. This is followed by the administration of sugammadex, an NMBA reversal agent, before nerve monitoring. One of the methods known for providing satisfactory intubation conditions while ensuring the quality of EMG signals during IONM in thyroid surgery is using rocuronium at an ED95 dose of 0.3 mg/kg. This approach is considered suitable for most IONM scenarios. However, when adequate muscle relaxation is not achieved, not all patients can undergo intubation, necessitating a strategy for appropriate intubation conditions.

Historically, it has been reported that achieving satisfactory intubation conditions without the use of NMBA during general anesthesia requires higher amounts of propofol and opioids. Therefore, the assumption is made that using remifentanil, an opioid used in total intravenous anesthesia (TIVA), at an appropriate concentration can provide acceptable intubation conditions with minimal NMBA use for patients undergoing IONM.

This study aims to determine the optimal concentration of remifentanil needed to achieve excellent intubation conditions in patients undergoing thyroid surgery with IONM using rocuronium 0.3 mg/kg as the NMBA during TIVA

Inclusion Criteria:

• All female aged 20-60
• ASA (American Society of Anesthesiologists) physical status I or II
• who scheduled for thyroidectomy under intraoperative neuromonitoring with a nerve integrity monitoring tube (NIM tube)

Exclusion Criteria:

• Patients anticipated to experience challenging intubation.
• Patients who have had an upper respiratory tract infection within the past 2 weeks.
• Patients with a history of heart, lung, and kidney diseases.
• Patients with a body mass index (BMI) of 30 kg/m² or higher.
• Patients currently taking analgesics.
• Patients expressing a desire not to participate in the study.

This is one arm non-randomized approach. Since it is a sequential approach of medication administration, the anesthesiologist and patients were blinded to whatever dose was given.