The propofol is administered until the patients loss of consciousness. Then 0.2 mg/kg esketamine is then administered by the anesthesiologist. After the administration of 0.2 mg/kg esketamine is completed, the endoscopist will begin the colonoscopic procedure.

The propofol is administered until the patients loss of consciousness. Then normal saline is then administered by the anesthesiologist. After the administration of normal saline is completed, the endoscopist will begin the colonoscopic procedure.

Both groups continued to receive the usual standard of gastroenterology care throughout the study period. The patients undergo preoperative preparation according to the requirements of colonoscopy. After entering the endoscopy room, the routine monitoring including electrocardiogram, heart rate, noninvasive blood pressure (BP), respiratory rate, and oxygen saturation (SpO2) are applied for patients. All monitoring data including HR, BP and SpO2 will be recorded at intervals of 3min. Safety assessments will be performed throughout the the research process. As a risk mitigation measure, esketamine should not be administered in patients with systolic blood pressure (SBP) > 140 mmHg or diastolic blood pressure (DBP) >90 mmHg prior to administration.

After the right upper limb venous access is opened, the patients is placed in the left lateral position. The oxygen mask is placed near the patients' nose and oxygen is provided by the mask for 6L/min during the colonoscopy.

The IBS Severity Scoring System (IBS-SSS) at baseline and at 6 weeks after colonoscopy, which incorporates five typical symptoms of IBS (intensity of abdominal pain, frequency of abdominal pain, intensity of bloating, dissatisfaction with bowel habits, associated interference with daily life) [54-56]. Each symptom score ranges from 0 to 100 and a higher score indicates a more severe symptoms of IBS. The parenteral symptoms incorporates nausea/vomiting, early satiety, heartburn, headache, backache, body aches, thigh pain, lethargy, excess wind, and urinary symptoms. Patients with IBS may be categorized according to IBS-SSS, which are asymptomatic (<75), mild (75-175), moderate (176-300), and severe (>300). A reduction of ≥50 points is considered clinical improvement.

The IBS Quality of Life (IBS-QOL) questionnaire at baseline and at 6 weeks after colonoscopy, which consists of 8 subscales (dysphoria, activity interference, personal image, health concerns, food avoidance, social reaction, sexuality, social relationship), with a total of 34 questions. Each subscale score ranges from 0 to 100 points. A higher score indicates a better quality of life.