Premedication With Simethicone and N-acetylcysteine in Improving Mucosal Visibility During Upper Endoscopy - a Prospective Double-blinded Randomized Controlled Trial

a. Study type: prospective, randomized, double-blinded, placebo-controlled trial: i. Prospective inclusion of patients; ii. Randomization by computer generated tables; iii. Allocation concealment by sealed, opaque envelopes; iv. Double-blinded - nurse instructed not to reveal treatment; patient and doctor unaware of treatment;

b. Patient selection: consecutive series of patients scheduled for upper gastrointestinal endoscopy; Exclusion criteria - sedation, previous total gastrectomy, known neoplasia or stenosis, allergies to simethicone or N-acetylcysteine, therapeutic or urgent procedures;

c. Sample size: 270 (3 groups of 90 patients): to improve "excellent" preparations from 20% (value from our own database) to 40% and assuming a normal distribution and a power of 80% (α=0.05), the calculated sample size of each of the 3 groups was 82; allowing for a 10% dropout rate, the sample size is 90 (270 patients overall); Groups: Group A - 100mL of water (placebo); Group B - 100mL of water plus 100mg Simethicone; Group C - 100mL of water plus 100mg Simethicone plus 600mg N-acetylcysteine;

d. Data collection methods: form sheet filled by nurses (appendix 1) and endoscopist (appendix 2);

e. Analysed variables: patients characteristics (age, gender), indication for endoscopy, time from administration to procedure, score of mucosal visualization, side effects of medication;