Research Article

Predictive Feasibility Of Colonoscopy Without Sedation Using A Nomogram Model

DOI:

10.3791/69881

⸱

February 17th, 2026

 ,  ,  ,  ,  , 
1Department of Anorectal, Dongzhimen Hospital, Beijing University of Chinese Medicine, 2Department of Surgery, Beixiaguan Community Health Service Center in Haidian District, 3Department of Digestive, Dongzhimen Hospital, Beijing University of Chinese Medicine

In This Article

Summary

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This study identifies risk factors for incomplete unsedated colonoscopy and develops a nomogram model (area under the receiver operating characteristic curve = 0.886) to guide clinical decision-making for patient selection and intervention optimisation.

Abstract

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Colorectal cancer poses a global burden, and colonoscopy is an effective screening tool, with unsedated colonoscopy offering distinct advantages but facing completion challenges. A retrospective analysis of 745 patients who underwent unsedated colonoscopy between July 2021 and August 2022 was conducted, with participants divided into completion (n = 670) and incompletion (n = 75) groups. Univariate analysis revealed significant differences in gender, age, constipation history, anxiety grade, postoperative Visual Analogue Scale scores and examiner experience between groups. Multivariate logistic regression identified constipation (odds ratio [OR] = 4.981, 95% confidence interval [CI]: 2.755–5.633), high anxiety (OR = 8.499, 95% CI: 4.987–10.212) and examination by a less-experienced physician (OR = 3.319, 95% CI: 2.673–4.732) as independent risk factors. The constructed nomogram model demonstrated good predictive accuracy (Hosmer–Lemeshow test: χ2 = 4.561, p = 0.683) and discriminative ability (area under the receiver operating characteristic curve = 0.886, 95% CI: 0.749–0.970). This model enables clinicians to identify high-risk patients preoperatively, optimise examination plan selection (e.g. recommending sedation) or implement intensive interventions, thereby improving the completion rate of unsedated colonoscopy and enhancing patient experience.

Introduction

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Colorectal diseases are prevalent among digestive disorders, with colorectal cancer poised to become a substantial global burden. It is anticipated that the incidence will surge by 60% to over 2.2 million new cases and will result in more than 1.1 million deaths by 20301. Colonoscopy is recognised as an effective method for screening colorectal cancer, substantially reducing cancer risk2,3. In addition, colonoscopy enhances the diagnosis and management of inflammatory bowel disease4,5. Sedation allows patients to undergo the procedure calmly and comfortably6. However, a sedation colonoscopy introduces certain challenges. For example, the anaesthetic drugs frequently used in painless colonoscopy can substantially affect vital signs, including hypotension or oxygen desaturation7. Perforation and bleeding constitute the most severe complications associated with this procedure8,9, and these can be reduced by unsedated procedures. Moreover, there is an increased likelihood of inducing colonic ischaemia when a colonoscopy is performed with sedation. This condition is thought to arise from the cardiovascular depressant effects of anaesthetic drugs, leading to diminished local blood flow in the intestine10.However, unsedated colonoscopy presents its own challenges regarding procedural success. Previous studies have reported completion rates for unsedated colonoscopy ranging from 80% to 90%, meaning that approximately 10% to 20% of patients fail to complete the examination due to pain or intolerance, compared to a significantly lower failure rate in sedated procedures6,7.

Compared with a painless colonoscopy, the risk of intestinal perforation is lower during colonoscopy without sedation. The operator is cautioned against blindly inserting the scope due to the patient’s response to pain, thereby reducing the risk of perforation11. There is no notable difference in symptoms, such as pain and abdominal distention, following the two types of examination12. However, a related literature review assessing global compliance with colonoscopy has reported generally unsatisfactory results, attributing this to a variety of factors13. The primary concern for patients undergoing colonoscopy without sedation is pain. Visceral nerve endings are sensitive to stimuli such as pulling, swelling, and forceful contractions, which can be induced by the actions of colonoscopy and the injection of substantial amounts of gas14. Patients opt for colonoscopy without sedation for various reasons, including 1) being able to communicate with the doctor during a conscious examination, 2) being able to work after the examination without waiting for the sedative drugs to metabolise, 3) not needing to be accompanied, 4) the lack of side effects from sedative drugs, 5) being able to drive immediately after the examination, 6) being able to warn the doctor of pain during the examination to avoid serious complications, 7) the short examination appointment time and 8) the reduced financial burden11. To enhance the patient experience of colonoscopy, improvements are needed in waiting times, satisfaction with preparation, and the clarity of post-colonoscopy instructions. Implementing interventions to improve the patient experience and the quality of colonoscopy is essential15. Specifically, identifying high-risk patients before the procedure is clinically important as it allows for proactive risk stratification. Instead of attempting an unsedated procedure that is likely to fail due to intolerance or poor preparation, clinicians can optimize the examination plan beforehand—for example, by recommending sedation for high-anxiety patients or prescribing extended bowel preparation protocols for those with constipation. This targeted approach minimizes the likelihood of mid-procedure termination, thereby reducing the rate of incomplete examinations and the need for repeat procedures. It is crucial to weigh the advantages and disadvantages of the two types of colonoscopies to select the most appropriate method for individual patient needs.

Unsedated colonoscopy is vital in colorectal cancer screening, presenting a valuable alternative to traditional sedated procedures. Although sedated colonoscopies often carry risks and potential complications, performing colonoscopy without sedation introduces unique challenges and benefits. This method is particularly relevant for patients who may not tolerate sedation well or who prefer to avoid its associated effects. There have been limited studies on the prognosis of patients’ ability to tolerate colonoscopy without sedation. Predictive models for colonoscopy outcomes without sedation rely on a range of patient demographic and clinical factors, as well as the experience of the performing endoscopist, to enhance procedural success and patient comfort16. By applying these insights, healthcare providers can better select appropriate candidates for sedation-free procedures and improve overall outcomes17. Existing predictive models for unsedated colonoscopy outcomes primarily focus on demographic and partial clinical factors but often overlook the complex interplay of psychological states and procedural variability16. The present study advances beyond these limitations by integrating three distinct dimensions—patient clinical history (constipation), psychological status (anxiety), and operator proficiency—into a single comprehensive nomogram. To the best of our knowledge, no current study has previously synergized these three key factors to predict unsedated colonoscopy outcomes, thereby providing a more accurate and personalized tool for clinical decision-making. This model is most suitable for outpatients aged 18–80 years undergoing unsedated colonoscopy and not suitable for patients with severe underlying diseases or contraindications to colonoscopy. Consequently, the primary aim of this study is to devise a predictive model for assessing the suitability of patients proposed for unsedated colonoscopy. This model aims to offer clinicians an initial tool to predict patients’ tolerance to the procedure, thereby enhancing the completion rate of the examination and alleviating patient concerns.

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Protocol

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This protocol adheres to the guidelines approved by the Ethics Committee of Dongzhimen Hospital, Beijing University of Chinese Medicine (Ethics No. 2023DZMEC-043-02). All participants provided written informed consent prior to the study enrolment.

Patient selection

The study was conducted between 30 July 2021 and 1 August 2022 and involved patients undergoing unsedated colonoscopy at Beijing University of Chinese Medicine. The following inclusion criteria were applied: patients were aged 18–80 years; written informed consent to participate was provided; and one or more of the following conditions were present: unexplained lower gastrointestinal bleeding, chronic diarrhoea, abdominal mass, lower/middle abdominal pain, suspected bowel tumour, suspected chronic bowel inflammation, or unexplained low-level bowel obstruction. Patients with the following conditions were excluded: inflammatory bowel disease, colorectal cancer, history of abdominal surgery or postoperative colon conditions, ileostomy, ischaemic bowel disease, intestinal obstruction, post-diverticulitis, insufficient bowel preparation, and severe underlying conditions (e.g. malignant hypertension, coronary heart disease with long-term anticoagulant use, poor cardiopulmonary function). Eligible patients were divided into completion and incompletion groups based on whether the colonoscopy reached the ileocecal junction or appendiceal fossa (documented in examination reports) using convenience sampling.

Pre-examination preparation

Patients were instructed to maintain a light diet for 3 days prior to the examination to reduce intestinal residue. First, 4 L of polyethylene glycol electrolyte powder solution was administered for bowel cleansing, with patients taking the laxative the night before the examination (with the total volume ingested over a period of 2-3 h). A 4–6 h interval was maintained between bowel preparation completion and colonoscopy to ensure optimal intestinal cleanliness. Patient compliance with the diet and laxative regimen was verified through verbal inquiry on the examination day.

Equipment and materials preparation

An electronic colonoscope (see Table of Materials for specifications) was prepared. The device was initialized with standard settings: standard white light imaging (WLI) mode was selected, and the air insufflation pump was set to a standard flow rate (level "Medium" or "High" depending on your device). A self-rating anxiety scale, Visual Analogue Scale (VAS) assessment form, Ottawa bowel preparation scale, and standardised data collection sheet. The availability of monitoring equipment (blood pressure monitor, pulse oximeter) and emergency supplies (oxygen, resuscitation equipment) in the examination room was checked, and all measurement tools (tape measure, stopwatch) were calibrated before use.

Examination procedure

The patient was placed in the left lateral position on the examination table, and their comfort was verified before initiating the procedure. The colonoscope was inserted through the anus under direct visualisation, advancing by following the intestinal physiological shape and adjusting direction to avoid wall injury. The time taken to reach the ileocecal valve from anus insertion was recorded using a stopwatch (starting at insertion, ending at visualisation of the ileocecal junction or appendiceal fossa). If the patient experienced severe discomfort (e.g. persistent abdominal pain, severe distension, palpitation, nausea) during the procedure, colonoscopy was immediately terminated, and the patient was transferred to the ward for observation and symptomatic treatment if necessary. Examinations were conducted by one of two board-certified gastroenterologists with distinct experience levels (see Endoscopist classification section).

Endoscopist classification

The endoscopists were classified according to the American Society for Gastrointestinal Endoscopy criteria and the Kudo classification system18. The experienced endoscopist (Physician 1) had ≥ 15 years of colonoscopy experience with > 7,500 total procedures (average 500/year), was Gongteng Grade IV (expert level), and had achieved caecal intubation times of < 10 minutes in > 90% of routine cases. The less-experienced endoscopist (Physician 2) had 8 years of experience with approximately 3,200 total procedures (average 400/year) and was Gongteng Grade III (proficient level). The endoscopist performing each examination was documented.

Data collection

Pre-examination demographic and clinical data collected: sex, age, body mass index (BMI), abdominal circumference (measured with a standard tape measure at the umbilical level), constipation history (diagnosed by the Rome IV criteria: ≥ 2 of 6 characteristic symptoms in the past 3 months) and anxiety level (assessed via the self-rating anxiety scale with 20 questions: total score < 50 = normal, 50–59 = mild anxiety [Grade 1], 60–69 = moderate anxiety [Grade 2], > 69 = severe anxiety [Grade 3])19,20.

Intra-procedural data collected: time to ileocecal junction and the reason for incomplete examination (if applicable: pain, poor bowel preparation, tumour stenosis).

Post-examination data collected: bowel preparation quality (evaluated by endoscopists immediately post-procedure using the Ottawa bowel preparation scale, categorised as excellent, good, moderate or poor) and pain level (assessed by nurses within 30 minutes post-procedure using the VAS: a 10 cm horizontal line, 0 = no pain and 10 = severe pain, with patients marking their self-perceived pain level)21. All data were recorded on a standardised collection sheet to ensure completeness and accuracy.

Statistical analysis

The collected data were entered into SPSS 26.0 software (IBM, Armonk, NY, USA) for analysis. Data normality was tested using the Kolmogorov–Smirnov method22. Normally distributed data were expressed as mean ± standard deviation, and comparisons between groups were performed using the t-test. Enumeration data were presented as cases or percentages, and the chi-squared (χ²) test was applied for group comparisons. Multivariate logistic regression analysis was performed, with colonoscopy completion status as the dependent variable (incomplete = 1, complete = 0) and variables with statistical significance in univariate analysis as independent variables (p < 0.05 considered significant). A nomogram model was developed using R software (version 4.2.0) with the rms package, with point values assigned to each independent risk factor based on regression coefficients. The nomogram was validated through bootstrap resampling (500 repetitions), evaluating predictive accuracy with the Hosmer–Lemeshow (H–L) deviation test and discriminative ability with the area under the curve (AUC) of the receiver operating characteristic curve. Clinical decision guidelines were established based on total risk scores, categorising patients into low-, moderate- and high-risk groups with corresponding intervention recommendations.

Quality control

All data collectors and endoscopists were trained on standardised procedures for data collection, examination performance and scale assessment to ensure consistency. Regular audits of collected data were conducted to check for completeness and accuracy, with discrepancies resolved immediately. Calibration of the measurement tools (tape measure, stopwatch, monitoring equipment) was checked before use.

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Results

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Comparison of clinical data between the two groups

A total of 745 patients underwent unsedated colonoscopy, including 220 patients with intermittent abdominal pain and 25 patients with a history of anxiety and taking anti-anxiety drugs, as shown in Figure 1. A total of 596 participants received an initial colonoscopy, and 149 participants received a repeat colonoscopy, with 65 receiving a sedation colonoscopy for the first time. A comparison of th...

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Discussion

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The main reasons for incomplete unsedated colonoscopy include patients’ low tolerance of discomfort or pain and relatively poor bowel preparation. The study indicates that a patient’s history of constipation, the examining physician’s experience, and the patient’s anxiety level all play a role in the feasibility of performing unsedated colonoscopy. Of the 332 patients with constipation included in the study, 57 were unable to complete the unsedated procedure. Chronic constipation, manifested by sy...

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Disclosures

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Not applicable.

Acknowledgements

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Not applicable.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Blood pressure monitorNot specifiedNot specifiedFor patient vital sign monitoring
Data collection sheetNot specifiedNot specifiedStandardized form for recording study data
Electronic colonoscopeOlympus (Japan)CF H260AIUsed for unsedated colonoscopy examination
Ottawa bowel preparation scaleNot specifiedNot specifiedUsed for bowel preparation quality evaluation
Oxygen supply equipmentNot specifiedNot specifiedEmergency supply for examination room
Polyethylene glycol electrolyte powder solutionNot specifiedNot specified4-L for bowel cleansing
Pulse oximeterNot specifiedNot specifiedFor patient oxygen saturation monitoring
R softwareR Foundation for Statistical ComputingVersion 4.2.0For nomogram model development (rms package)
Resuscitation equipmentNot specifiedNot specifiedEmergency supply for examination room
Self-rating anxiety scaleNot specifiedNot specified20-item scale for anxiety assessment
SPSS softwareIBMVersion 26.0For statistical analysis
Standard tape measureNot specifiedNot specifiedFor measuring abdominal circumference
StopwatchNot specifiedNot specifiedFor recording time to ileocecal junction
Visual Analogue Scale (VAS) assessment formNot specifiedNot specified10 cm scale for pain assessment

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Tags

Unsedated ColonoscopyColonoscopy CompletionNomogram ModelColorectal Cancer ScreeningPredictive AccuracyLogistic RegressionAnxiety GradeConstipation HistoryExaminer ExperienceVisual Analogue Scale

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