This is a prospective, endoscopist-blinded, randomized controlled study. The study protocol was approved by the Institutional Review Board of Kosin University Gospel Hospital (KUGH 2014-07-074). Patients aged >30 years who were undergoing screening colonoscopy at the health examination center of Kosin University Gospel Hospital in Korea were enrolled. Patients with a history of abdominal surgery, inflammatory bowel disease, chronic kidney disease, heart failure, ascites, ileus or intestinal obstruction, or allergy to bowel preparation drugs and those who were pregnant were excluded. Written informed consent was obtained from all participants before enrollment in this study. All patients listened to explanations about the study purpose given by a well-trained nurse in the health examination center. The nurse provided education with an informational brochure on colonoscopy, which included the diet schedule (low-fiber diet for three days and soft diet for dinner the day before the colonoscopy), administration method of the bowel preparation regimen, process of colonoscopic examination, and side effects of the regimen. Then, subjects were randomized to either the SMM or control group using the table of random numbers. Patients in the SMM group received two video clips sent via KakaoTalk, whereas those in the control group did not receive any video clips.

A study investigator (SCJ) created two video clips introducing the diet and regimen for colonic cleansing before colonoscopy. The first video clip introduced the diet for colonic cleansing before colonoscopy. In this video clip, a low-fiber diet for three days and soft diet for dinner the day before the colonoscopy were recommended, and foods to avoid including watermelon, oriental melon, grape, nut products, kimchi, vegetables, and seaweed were emphasized. The second video clip introduced the regimen for bowel preparation. This video clip explained the detailed preparation method of the polyethylene glycol electrolyte powder (PEG-ELP), which involved drinking 500 mL water after consuming 1 L PEG-ELP between 9:00 and 11:00 p.m. on the day before colonoscopy and drinking an additional 500 mL water after consuming 1 L PEG-ELP between 5:00 and 7:00 a.m. on the day of the colonoscopy. Each video clip was approximately 2-min long.

On the day of the colonoscopy, all patients were interviewed by a study investigator (SCJ), and they filled out a questionnaire on aspects such as the viewing of each video, types of food consumed, start time of initial bowel preparation, time of final bowel preparation, and last stool color. Patient compliance was assessed as good or bad based on the food types consumed and time of bowel preparation. Side effects were categorized as mild, moderate, or severe. Colonoscopic examinations were performed by one experienced endoscopist (SJK) who was blinded to the group information. All colonoscopic examinations were performed between 09:00 a.m. to 01:00 p.m. During the examination, insertion time, withdrawal time, polyp detection, and bowel preparation scale were recorded. The bowel preparation scale was assessed according to the Ottawa bowel preparation scale [10], with a score of 0-4 for the rectosigmoid, middle, and right colon and 0-2 for quantity of residual fluid. The total score was calculated by summing all scores. The scale ranges from 0 (perfect) to 14 (inadequate). When a polyp was detected during colonoscopic examination, biopsy and histologic assessments were performed to identify the adenoma component. Then, the polyp detection rate (PDR) (the number of colonoscopies in which one or more polyps were detected divided by the total number of colonoscopies) and adenoma detection rate (ADR) (the number of colonoscopies in which one or more adenomas were detected divided by the total number of colonoscopies) were assessed.

The primary endpoint in this study was the quality of the bowel preparation, which was assessed by the endoscopist using the Ottawa scale. Adequate bowel preparation was defined as an Ottawa score of <6 at the time of colonoscopy. Secondary endpoints were colonoscopic insertion and withdrawal time, PDR, ADR, side effects during bowel preparation, and rate of sleep disturbance due to bowel preparation. Severe side effects were defined as ≥10 nausea/vomiting episodes or intolerable abdominal pain/discomfort.

The number of patients in each group was calculated with an alpha of 0.05 and a power of 0.8, assuming a 12% difference in the rate of colonic cleansing based on previous studies. Accounting for a dropout rate of 10%, at least 153 subjects in each group were needed for the study. Continuous data with normal distributions are expressed as mean±standard deviation, and categorical data are presented as the number of subjects (%). Student’s t-test and the chi-square test were performed for continuous and categorical variables, as appropriate. To analyze the factors associated with adequate bowel preparation, univariate and multivariate logistic regression analyses were performed. P-values of <0.05 were considered statistically significant. Statistical analyses were performed using SPSS version 23.0 (IBM Co., Armonk, NY, USA).

Between August and November 2014, 306 patients signed written informed consent forms and were randomized to the SMM and control groups. After randomization, 25 patients cancelled appointments and did not undergo colonoscopy. Finally, 140 patients from the SMM group and 141 patients from the control group underwent colonoscopic examination. The patient selection flowchart is presented in Fig. 1. Baseline characteristics are summarized in Table 1. The mean age of all participants was 48.3±9.9 years, and 161 (57.3%) patients were men. Patients in the SMM group were significantly younger and had lower body mass index (BMI). All participants performed bowel preparation with PEG-ELP.

As shown in Table 2, there were no significant differences between the two groups in the assessment of patient compliance, status of last defecation after bowel preparation, and adequate bowel preparation according to the Ottawa score (<6). In the SMM group, the odds ratio predicting adequate bowel preparation (Ottawa score <6) was 1.39 (95% confidence interval, 0.87–2.22; p=0.171). The result did not change appreciably after adjusting for age, sex, BMI, and previous experience of colonoscopy. However, the total Ottawa score was significantly lower in the SMM group than in the control group (5.47±1.74 vs. 5.97±1.78, p=0.018). In particular, the Ottawa scores for the right and middle colon were significantly lower in the SMM group than in the control group (right colon, 1.99±0.59 vs. 2.12±0.52, p=0.035; middle colon, 1.48±0.67 vs. 1.67±0.64, p=0.013). These results were particularly prominent in the younger age group; the total Ottawa score of patients in the SMM group aged <40 years was significantly lower than that of patients in the control group aged <40 years (5.10±1.55 vs. 6.22±2.33; p=0.034, Table 3). However, these differences between the two groups were not significant in patients aged >40 years. Under 40 years of age, the patient compliance was significantly better in the SMM group than in the control group (data not shown). Between the two groups, the differences in cecal intubation time, severe symptoms during bowel preparation, and sleep disturbances were not significant, whereas the withdrawal time was longer in the control group than in the SMM group, and PDR and ADR were higher in the control group than in the SMM group (Table 4).