Colonoscopy is the most effective method for screening for colon cancer and precancerous lesions. However, the effectiveness of colonoscopy is highly dependent on the quality of bowel preparation. To identify patients at high risk of bowel preparation failure, it is necessary to explore and analyze the risk factors for bowel preparation failure in colonoscopy patients and to develop an effective and distributive prediction model. Consequently, high-risk patients can receive intensive protocols and interventions, while low-risk patients can be prevented from taking excessive amounts of laxatives, thereby improving bowel preparation without increasing adverse effects.
In this study, patients aged ≥ 60 years were more likely to fail bowel preparation, and this has been associated with declining gastrointestinal motility, frequent concomitant disease and medication history, or limited or poorly tolerated physical activity. Comorbidities and medication history are the leading causes of bowel preparation failure among elderly patients, compared to other factors attributed to age [12]. In this study, the covariance analysis of age with related factors showed no significant covariance between age and other factors. Therefore, age ≥ 60 years was an independent risk factor for bowel preparation failure in patients undergoing colonoscopy.
Men had an independent risk factor for bowel preparation failure. Baker et al. [13] conducted a retrospective study on 28,725 patients. Higher incidence of bowel preparation failure was observed in men than in women (56.6% vs. 43.4%), and men were associated with bowel preparation failure (OR = 1.353). This could be attributed to poorer compliance with bowel preparation protocols by men. In this study, women were more attentive to bowel preparation details during colonoscopy appointments than men and repeatedly confirmed with the appointment staff the dietary choices and timing of laxative administration in the bowel preparation protocol. Therefore, health education should be enhanced for male patients scheduling colonoscopies to emphasize the importance of bowel preparation prior to the examination. This can ensure patients restrict their diet and adhere to laxatives administration timing.
BMI ≥ 24 was an independent risk factor for bowel preparation failure in patients undergoing colonoscopy. Similarly to the results of this study, Borg et al. [14] showed that patients with a BMI > 25 had a greater risk of bowel preparation failure. A prospective study by Sharara et al. [15] showed that a BMI < 20 (underweight) was a risk factor for bowel preparation failure. In a prospective study conducted by Fok et al. [16], no statistically significant difference was found between obese and non-obese patients regarding bowel preparation. Oral sodium picosulfate was used in their study. The differences between the results of the above studies and the current study may be attributed to the different study populations, study designs, BMI classification criteria, and bowel preparation procedures. In this study, according to the BMI classification standard of Chinese population, BMI ≥ 24 was considered overweight. The findings of this study showed that overweight patients are more likely to experience bowel preparation failure, possibly because of physical inactivity, chronic constipation, and multiple chronic illnesses.
It was also observed that smokers are more likely to fail bowel preparation. When smoking results in greater sympathetic excitability, bowel movements are slowed. Moreover, chronic smoking is associated with a number of diseases and poses high risk of comorbidity. Furthermore, smokers are less likely to be health conscious and less likely to comply with bowel preparation protocols. Accordingly, patients who smoke should be encouraged to quit smoking and health education should be provided during bowel preparation.
Constipation was found to be an independent risk factor for the failure of bowel preparation before colonoscopy. This is consistent with the findings of Gimeno-García et al. [17] In a prospective cohort study of 409 patients undergoing colonoscopy, Fang et al. [18] also identified chronic constipation as an independent risk factor for bowel preparation failure (OR = 2.05). As a result of decreased autonomic nervous system function, relaxation, slowed peristalsis, and reduced activity of the intestinal muscles, constipated patients are more likely to experience prolonged bowel emptying times and weakness in defecation. This increases the amount of feces remaining in the intestinal lumen and adversely affects the quality of bowel preparation. In China, chronic constipation affects 4–10% of adults and shows an upward trend. Therefore, healthcare professionals are advised to follow up with patients experiencing constipation after undergoing colonoscopy. It is recommended that patients with constipation eat a low residue diet 3 days prior to the examination and take high-dose bowel cleansing medications and adjunctive bowel medications as prescribed by their physician in order to reduce the likelihood of bowel preparation failure.
Patients with diabetes mellitus are more likely to experience failure of bowel preparation. As gastric motility and emptying are regulated by blood glucose, an increase in blood glucose inhibits gastric emptying and slows down gastrointestinal transport, and diabetes mellitus in later stages leads to peripheral and autonomic neuropathy, resulting in abnormal gastrointestinal function in diabetics, which can lead to constipation in 90% of cases. While Izzy et al. [19] reported that bowel preparation failure in diabetic patients was not associated with short-term glycemic control. Further research is needed to examine the relationship between glycemic control and bowel preparation in diabetics.
In terms of the relationship between previous abdominal surgical history and the quality of bowel preparation, no definitive conclusion was made in this study. According to Chung et al. [20], detailed classification of prior surgical history, appendectomy, hysterectomy, and colorectal resection were independent risk factors for bowel preparation failure. While a history of abdominal surgery was not found to be an important factor in bowel preparation failure in Cheng et al. [21], possibly because the study did not clearly define the various types of abdominal surgery. This study examined the relationship between abdominal surgery, colorectal surgery, gastric/duodenectomy, appendectomy, and hysterectomy, and the quality of bowel preparation in colonoscopy patients. A history of colorectal surgery was found to be a risk factor independently associated with failure of bowel preparation. Owing to altered intestinal anatomy and adhesions, patients after colorectal surgery experienced reduced bowel motility and emptying ability, and intestinal lumen contents remained in their bowels, thereby reducing the quality of their bowel preparation [22]. Therefore, healthcare professionals can encourage patients undergoing colonoscopy with a history of colorectal surgery to engage in moderate-intensity aerobic exercise, such as walking, and massage their abdomen during medication administration to promote intestinal peristalsis, in addition to a comprehensive bowel preparation program.
The prediction model for the risk of failure of bowel preparation established in this study showed a good predictive effect. The areas under the ROC curves of the modeling and validation groups were 0.732 and 0.713, respectively. The Hosmer-Lemeshow χ2 test for the prediction model was P > 0.05. The calibration plots showed good agreement between the model prediction probability and the actual occurrence probability. The areas under the ROC curve ranged from 0.63 to 0.72 in the published studies [11–13]. The model of this study has been presented as an alignment diagram, which is easier to visualize and is convenient for clinical use. When patients schedule appointments for colon examinations, the medical staff at the endoscopy center can use this alignment diagram to predict the probability of failure of the bowel preparation process and provide personalized bowel preparation plans. Notwithstanding its success, this study has limitations. This was a single-center study and the model used had only internal validation. A multicenter and large-sample studies will be necessary to validate the model externally and assess its predictive ability.