Effect of Simethicone on Bowel Preparation for Colonoscopy

1. Study design: endoscopist-blinded, prospective, randomized controlled trial 2. Subjects \- A single-center, randomized, observer-blinded study was performed at Korea University Hospital in Anam. Outpatients were prospectively enrolled. Each group of the patients will receive PEG-Asc or PEG-Asc with simethicone before colonoscopy. 3. Sampling design: Consecutive recruitment of consenting patients 4. Variables Predictor 1. group 1 (PEG-Asc) received 1 L solution of PEG-Asc at 7 p.m the evening before colonoscopy and another 1 L solution of PEG-Asc at 5 hours before procedure; 2. group 2 (PEG-Asc with simethicone) received 1 L solution of PEG-Asc at 7 p.m the evening before colonoscopy and another 1 L solution of PEG-Asc at 5 hours before procedure;Two packs (200 mg/10 mL each) of simethicone (400 mg) was mixed with last 500 mL of additional clear fluid. 5. Primary Outcome: Quality of bowel preparation \[Boston Bowel Preparation Scale, bubble score\] 6. Secondary Outcome: Patients and endoscopists' compliance\[Tolerability, palatability of patient, fatigue score of endoscopist\]