The Appropriate Remifentanil Dose for Optimal Insertion of Laryngeal Mask Airway in Adult Patients During Induction of General Anesthesia Using Remimazolam.

1.Screening Method:

• Subject screening is conducted based on the results of general preoperative tests, including checking the patient's medical and medication history, routine blood tests, general chemistry and coagulation tests, electrocardiogram (ECG), chest X-ray, etc.
• Subjects are selected from adult patients undergoing elective surgery under general anesthesia using the LMA within 3 hours.
• Patients are visited the day before the surgery. Information about the study is provided and patients are allowed sufficient time for deciding participation until arriving at the operating room. Informed consent for the participation is achieved on the morning of surgery.

2.Research Method:

• Monitoring devices, including electrocardiogram, non-invasive blood pressure monitor, pulse oximeter, and SedLine® brain function monitor (Masimo, Irvine, CA), are applied for patient monitoring according to standard care.
• Proper insertion of the intravenous catheter in the patient is confirmed. The intravenous line is connected to remifentanil and remimazolam (diluted to concentrations of 20μg/mL and 1mg/mL respectively) using syringe pumps.

(3)100% oxygen is administered at 6L/min for 3 minutes for preoxygenation. (4)Continuous infusion of remifentanil is started using Target-Controlled Infusion (TCI) with the Minto model, adjusting the effect-site concentration based on the biased-coin up-and-down method. The initial concentration for the first patient is 3.0μg/mL. Subsequent doses are determined based on the success or failure of the previous subject's LMA insertion. 0.3mg/kg of remimazolam is simultaneously administered over approximately 10-20 seconds.

(5)100% oxygen is supplied through a facemask and manual ventilation is performed if necessary. When the desired effect-site concentration of remifentanil is confirmed 120 seconds after remimazolam administration, LMA is inserted. The LMA used for the procedure is Ambu®AuraGainTM (Ambu A/S, Ballerup, Denmark). The size of the LMA is selected according to the manufacturer's guide and lubricating jelly is applied on the LMA before the insertion.

(6)If the LMA is determined to obstruct the airway or be malpositioned, it is removedand mask ventilation is reengaged. The effect-site concentration of remifentanil is increased by 0.3μg/mL, and one minute later, the LMA is inserted for the second time using the same procedure. If the insertion proves unsuccessful despite three attempts following the same approach, tracheal intubation is performed.

(7)Data are collected during LMA insertion and maintenance. Continuous infusion of remimazolam and remifentanil is conducted to maintain PSI score in the range of 25-50 during the surgery. Infusion of the anesthetic agents are stopped when the surgery is finished. The LMA is removed after spontaneous breathing is confirmed and the patient is transferred to the recovery room.

Inclusion criteria

• Patients aged 19 years or older and less than 65 years
• ASA physical status classification I, II, or III
• Scheduled for elective surgery lasting within 3 hours under general anesthesia using a laryngeal mask

Exclusion criteria

• Refusal to participate in the study
• Unable to read the consent form or comprehend the research process (e.g., illiteracy, foreign nationality, cognitive impairment)
• Anatomic structures that are anticipated to cause difficulty in mask ventilation
• History of difficulty in airway management
• Upper respiratory infections or respiratory conditions (e.g., asthma, pneumonia)
• Risk of aspiration (e.g., gastroesophageal reflux)
• Allergies to anesthesia-related drugs, such as benzodiazepines or opioid analgesics
• Impaired liver or kidney function
• Pregnant or breastfeeding patients
• Obesity (body mass index > 30 kg/m2)
• History of drug or alcohol abuse.