Postoperative sore throat (POST) is a common complication following general anesthesia involving endotracheal intubation, often leading to decreased patient satisfaction. The TaperGuard™ endotracheal tube (ETT) features a tapered-shaped cuff designed to reduce micro-aspiration and has been shown to result in a lower incidence of POST compared to conventional cylindrical ETTs. While previous studies using standard cylindrical ETTs suggested that a smaller inner diameter (ID) reduces the risk of POST, this relationship has not been fully established specifically for the TaperGuard™ ETT.

This study aims to compare the incidence of POST between a standard-sized TaperGuard™ ETT (ID 7.0 mm) and a smaller-sized TaperGuard™ ETT (ID 6.0 mm) in female patients. The investigators hypothesize that using a smaller ID TaperGuard™ ETT will significantly reduce the occurrence of POST within 24 hours after surgery.

Patients will be randomly assigned to either the control group (ID 7.0 mm) or the small group (ID 6.0 mm). Throughout the procedure, cuff pressure will be strictly maintained at 22 cmH2O to minimize mucosal damage. The primary outcome is the presence of sore throat, and secondary outcomes include the severity of the pain and the incidence of hoarseness at several time points up to 24 hours postoperatively.

1. Background and Rationale Postoperative sore throat (POST) is a frequent complication following general anesthesia with endotracheal intubation, significantly impacting patient satisfaction. The mechanism of POST involves localized trauma and subsequent inflammatory responses or mucosal edema caused by the endotracheal tube (ETT) and its cuff. The TaperGuard™ ETT, designed with a tapered polyvinyl chloride cuff, aims to reduce micro-aspiration compared to conventional cylindrical ETTs. Previous studies have demonstrated that the TaperGuard™ ETT results in a lower incidence of POST than cylindrical ETTs. Additionally, while research on cylindrical ETTs has shown that a smaller inner diameter (ID) correlates with a lower incidence of POST, this effect has not been specifically validated for the TaperGuard™ ETT. This study aims to evaluate whether using a one-size smaller TaperGuard™ ETT (ID 6.0 mm) further reduces POST compared to a standard size (ID 7.0 mm) in female patients.

2. Study Population and Randomization Female patients aged 19 to 70 with an ASA physical status of I-III scheduled for surgery under general anesthesia in the supine or lithotomy position will be enrolled. Participants will be randomly assigned to either the Control Group (Group C: ID 7.0 mm) or the Small Group (Group S: ID 6.0 mm) using a computer-generated random number sequence.

3. Anesthesia Protocol Induction: After 5 minutes of preoxygenation, anesthesia will be induced using intravenous lidocaine (40 mg), propofol (2 mg/kg), and rocuronium (0.8 mg/kg).

   Intubation: Tracheal intubation will be performed using direct laryngoscopy. The ETT position will be confirmed via a fiberoptic bronchoscope to be 4 cm above the carina. The cuff will be inflated with air, and the pressure will be strictly adjusted to 22 cmH2O using a manometer.

   Maintenance: Anesthesia will be maintained with sevoflurane (1.5-3.0%) and remifentanil (Target-Controlled Infusion, 2-3 ng/mL). Mechanical ventilation will be set to a tidal volume of 8 ml/kg and a respiratory rate of 10-12 cycles/min to target an EtCO2 of 30-35 mmHg.

4. Emergence and Recovery Five minutes before the end of surgery, fentanyl (50 mcg) will be administered intravenously. Upon completion of surgery, sevoflurane and remifentanil will be discontinued, and sugammadex (100 mg) will be administered for neuromuscular blockade reversal. Extubation will be performed when the patient's spontaneous tidal volume exceeds 200 ml and they follow verbal commands to open their eyes.

5. Outcome Assessment A blinded co-investigator, who is not involved in the anesthesia administration, will assess the presence and severity of POST and hoarseness. Assessments will be conducted at four time points: immediately upon arrival at the Post-Anesthesia Care Unit (PACU), and at 1, 6, and 24 hours postoperatively. The severity of POST will be recorded using an 11-point Numerical Rating Scale (NRS).

Inclusion Criteria:

• Female patients.
• Aged between 19 and 70 years.
• American Society of Anesthesiologists (ASA) physical status I, II, or III.
• Patients scheduled to undergo elective surgery under general anesthesia requiring endotracheal intubation.
• Patients undergoing surgery in the supine or lithotomy position.
• Patients who voluntarily provide written informed consent after receiving a full explanation of the study's purpose and procedures

Exclusion Criteria:

• Predicted difficult intubation.
• Confirmed diseases or anatomical abnormalities of the head and neck, including the pharynx and larynx.
• Presence of preoperative sore throat.
• Risk of pulmonary aspiration.
• Requirement for the prone position or other surgical positions where airway management with a TaperGuard™ ETT is difficult.
• Scheduled for head and neck surgery or other procedures where the use of a TaperGuard™ ETT is challenging.
• Potential pregnancy.
• Inability to provide informed consent or make a decision to participate after receiving the study explanation

Only female patients are included in this study to ensure a homogeneous study population and to minimize confounding factors related to gender-specific differences in airway anatomy and the incidence of postoperative sore throat (POST). This approach allows for a direct comparison with previous clinical data that established the standard endotracheal tube (ETT) size (ID 7.0 mm) for female adults as a reference point for investigating the effects of a smaller ETT size.

De-identified individual participant data that underlie the results reported in this article (text, tables, figures, and appendices) will be made available.

Beginning 6 months and ending 3 years following article publication.

Researchers whose proposed use of the data has been approved by an independent review committee identified for this purpose. Proposals should be directed to the corresponding author.