Suboptimal bowel preparation adversely affects colonoscopy quality, increases healthcare costs, and prolongs waiting time. The primary contributing factors include poor tolerance to the preparation solutions, noncompliance with prescribed instructions, and suboptimal efficacy of the bowel cleansing solution itself.

This review examined the predictive factors associated with suboptimal bowel preparation and discussed interventions aimed at improving bowel cleansing. It also provides evidence-based practical algorithms supplemented by insights from our own clinical experience. Relevant topics were reviewed using resources from the PubMed database.

Although current bowel preparation protocols are effective for the majority of patients, a significant proportion still present challenges for optimal preparation. These patients may benefit from personalized strategies tailored to the specific causes of preparation failure. Conducting a thorough interview is crucial for identifying the reasons for failure, particularly in patients who have previously experienced suboptimal preparation during colonoscopy. In colonoscopy-naïve patients, it is essential to assess the risk of suboptimal preparation. In both cases, interventions should be customized to either address the identified causes in the former group or employ preventive strategies to reduce the likelihood of failure in the latter.

Polyethylene glycol (PEG) is considered the gold standard regimen for bowel preparation; however, due to the necessity of a large volume, patient tolerance is impaired. Therefore, lactulose is a novel alternative for colonoscopy preparation. This study aimed to investigate the efficacy and safety of lactulose-based bowel preparations in comparison with PEG for colonoscopy.

This is a prospective, non-blinded, comparative study. Outpatients were randomly divided into two groups: group 1 (111 patients), PEG; and group 2 (111 patients), lactulose. The following clinical outcomes were assessed in each group: degree of bowel clearance using the Boston bowel preparation score, colorectal polyp detection rate, adenoma detection rate, tolerability, and side effects.

The rate of inadequate bowel preparation was 8.1% and 1.8% for the PEG and lactulose groups, respectively (p=0.030). The Boston bowel preparation score for the entire colon was 7.34±1.17 and 8.36±1.09 for the PEG and lactulose groups, respectively (p<0.001). The satisfactory overall experience rates were 27.9% and 62.2% for the PEG and lactulose groups, respectively (p<0.001).

The novel bowel preparation with oral lactulose was superior to that with PEG in terms of colon cleansing, adenoma detection rate, tolerance, and patient experience.

Adequate bowel preparation (BP) is crucial for the diagnosis of colorectal diseases. Identifying patients at risk of inadequate BP allows for targeted interventions and improved outcomes. We aimed to develop a model for predicting inadequate BP based on preparation-related factors.

Adult outpatients scheduled for colonoscopy between May 2022 and October 2022 were enrolled. One set (N = 913) was used to develop and internally validate the predictive model. The primary predictive model was displayed as a nomogram and then modified into a novel scoring system, which was externally validated in an independent set (N = 177). Inadequate BP was defined as a Boston Bowel Preparedness Scale (BBPS) score of less than 2 for any colonic segment. The model was evaluated by the receiver operating characteristic (ROC) curve, calibration plots, and decision curve analysis (DCA).

Independent factors included in the prediction model were stool frequency ≤ 5 (15 points), preparation-to-colonoscopy interval ≥ 5 h (15 points), incomplete dosage (100 points), non-split dose (90 points), unrestricted diet (88 points), no additional water intake (15 points), and last stool appearance as an opaque liquid (0-80 points). The training set exhibited the following performance metrics for identifying BP failure: area under the curve (AUC) of 0.818, accuracy (ACC) of 0.818, positive likelihood ratio (PLR) of 2.397, negative likelihood ratio (NLR) of 0.162, positive predictive value (PPV) of 0.850, and negative predictive value (NPV) of 0.723. In the internal validation set, these metrics were 0.747, 0.776, 2.099, 0.278, 0.866, and 0.538, respectively. The external validation set showed values of 0.728, 0.757, 2.10, 0.247, 0.782, and 0.704, respectively, indicating strong discriminative ability. Calibration curves demonstrated close agreement, and DCA indicated superior clinical benefits at a threshold probability of 0.73 in the training cohort and 0.75 in the validation cohort for this model.

This novel scoring system was developed from a prospective study and externally validated in an independent set based on 7 easily accessible variables, demonstrating robust performance in predicting inadequate BP.

Adequate bowel cleansing is essential for colonoscopy quality. A novel 1 L polyethylene glycol plus ascorbate (1 L PEG+ASC) solution has been recently introduced. Nevertheless, the efficacy of 1 L PEG+ASC as compared to that of high-volume bowel preparation in both inpatients and outpatients is still unclear.

This single-blinded, non-inferiority study randomized patients undergoing colonoscopy to receive split-dose 1 L PEG+ASC or 4 L PEG. The primary endpoint was the overall cleansing success. Secondary endpoints were excellent cleansing and high-quality cleansing of the right colon, as well as lesions detection rate, patient compliance, tolerability and safety.

Overall, 478 patients were randomized to 1 L PEG+ASC (N = 236) or 4 L PEG (N = 242). The 1 L PEG+ASC showed higher cleansing success rate (91.8% vs 83.6%; P=0.01) and a high-quality cleansing of the right colon (52.3% and 38.5%; P=0.004) compared to 4 L PEG. Moreover, 1 L PEG+ASC achieved a higher cleansing success in out-patients (96.3%% vs 88.6%; P=0.018), and a similar success rate in the in-patients (84.7% vs 76.7%; P=0.18). Adenoma detection rate, tolerability and incidence of adverse events were comparable between preparations.

The 1 L PEG+ASC showed higher efficacy in achieving adequate colon cleansing compared with 4 L PEG, particularly in the right colon. No differences in the tolerability and safety were detected.

A 1-L polyethylene glycol plus ascorbate (PEG-ASC) preparation has been recently developed to improve patients' experience in colonoscopy. This meta-analysis aimed to evaluate the effectiveness and safety of 1-L PEG-ASC compared with those of other bowel preparations for colonoscopy.

MEDLINE, Embase, Scopus, and the Cochrane Library were systematically searched for randomized controlled trials comparing 1-L PEG-ASC with other bowel preparations published through July 2022. A random-effects model was applied for pooling the results; heterogeneity was expressed as I2.

Nine studies met the inclusion criteria and were included. The analysis showed significantly higher cleansing success (CS) (OR = 1.50; 95% CI = 1.25-1.81; p < 0.01, I2 = 0%) and right-colon high-quality cleansing (HQC) (OR = 1.67; 95% CI = 1.21-2.31; p < 0.01, I2 = 43%) with 1-L PEG-ASC compared to the other preparations. The pooled estimate of the adenoma detection rate (ADR) did not significantly differ between the two groups either in the overall (OR = 1.02; 95% CI = 0.87-1.20; p = 0.79, I2 = 0%) or split-dosing regimen subgroup analysis (OR = 0.99; 95% CI = 0.84-1.18; p = 0.94, I2 = 0%). A significantly higher pooled estimate of the number of patients with adverse events (AEs) (OR = 1.51; 95% CI = 1.23-1.84; p<0.01, I2 = 0%) and incidence of AEs (IRR=1.33; 95% CI = 1.11-1.58; p<0.01, I2 = 71%) was observed with 1-L PEG-ASC than with the other preparations. No serious AEs or deaths occurred.

Compared to other preparations, 1-L PEG-ASC yielded higher overall CS, higher right-colon HQC rates, and similar ADR. The number of patients with AEs and incidence of the total AEs were significantly higher with 1-L PEG-ASC in the absence of serious AEs.

Several risk factors affecting the adequacy of colon cleansing have been proposed during the last decades. However, less is known about the impact that atmospheric aspects could have on adequacy of the bowel cleansing. The study aimed to investigate if the atmospheric temperature could impact on the bowel cleansing during colonoscopy.

A prospective maintained database of the colonoscopies performed since 1st August 2017 to 31st March 2020 was retrospective reviewed. The primary outcome of the study was to identify if the atmospheric temperature was associated with inadequate colon cleansing during colonoscopy. Secondary outcome was to identify the other factors associated with an inadequate colon cleansing.

One thousand two hundred twenty patients were enrolled. High atmospheric temperature (> 25 °C) significantly influenced the colon cleansing (p < 0.0001). Adequate colon cleansing was negatively influenced by gender (female patients were associated with higher colon cleansing rate, p = 0.013), diabetes (p < 0.0001), previous pelvic surgery (p = 0.001), use of Beta-Blocker (p = 0.001), anti-platelet (p = 0.017), angiotensin converting enzyme inhibitors (p = 0.001), the adoption of 4 L Poly Ethylene Glycol solution (p = 0.009), single-dose regimen (p < 0.0001) low patients' compliance (p < 0.0001), higher age and body mass index (p < 0.0001 and p = 0.025), lower education levels (p < 0.0001). On the contrary, admission to the ward to perform bowel preparation positively impacted on colon cleansing (p = 0.002).

Atmospheric temperature could play an important role in the colon cleansing during colonoscopy, being high temperature (> 25 °C) associated with lower rate of adequate bowel cleansing. However, being this relationship never studied before, these results must be confirmed by other studies.

One-day low-residue diet (LRD) is recommended before colonoscopy, but only three single-center trials compared the 1-day versus 3-day LRD. The aim of this multicenter study was to compare the impact of a 3-day versus 1-day LRD on its ability to adequately and successfully prepare the bowel of outpatients that require a colonoscopy. The outpatients' tolerance and adherence to the LRD were also considered.

Consecutive outpatients were randomized to 1-day versus 3-day LRD at three open-access endoscopy units. The primary endpoint consisted of the proportion of patients with a satisfactory degree of bowel cleanliness (Score 2-3 on the Boston Bowel Preparation Scale [BBPS] in each segment). Secondary endpoints were patients' tolerance and adherence to the prescribed diet evaluated by a standardized questionnaire.

289 patients were included in the study (1-day LRD arm = 143, 3-day LRD arm = 146). BBPS ≥2 was not significantly different in the two dietary regimens in any of the three colonic segments (71% vs. 72%, p = 0.9). The percentage of patients with incomplete preparation was similar in the two arms (9% vs. 9%; p = 1.0). No significant differences were found among colonoscopy findings in terms of abnormalities (81% vs. 84%, p = 0.8). Both groups scored similarly in overall tolerance to LRD (48% vs. 49%, p = 1.0) and also in whether they would have adopted a different dietary regimen (p = 0.3).

Our multicenter randomized study confirmed that optimal bowel cleansing is reached through a 1-day LRD.

Factors affecting the quality of bowel preparation for colonoscopy in the elderly are not fully known, and current guidelines provide no specific recommendations. This study aimed to assess the difference in bowel cleansing in young and elderly patients and evaluate predictors of bowel cleansing in the elderly. We retrospectively reviewed a prospective cohort of 1289 patients performing colonoscopy after a 1-, 2-, or 4-L PEG-based preparation. All 1289 were included in the analysis. Overall, 44.6% of patients were aged ≥65 years. Cleansing success (CS) was achieved in 77.3% and 70.3% of patients aged <65 years and ≥65 years, respectively. At multivariable analysis, split regimen (OR = 2.43, 95% CI = 1.34−4.38; p = 0.003), adequate cleansing at previous colonoscopy (OR = 2.29, 95% CI = 1.14−4.73; p = 0.02), tolerability score (OR = 1.29, 95% CI = 1.16−1.44; p < 0.001), a low-fiber diet for at least 3 days (OR = 2.45, 95% CI = 1.42−4.24; p = 0.001), and colonoscopy within 5 h after the end of preparation (OR = 2.67, 95% CI = 1.28−5.56; p = 0.008) were independently associated with CS in the elderly. Combining a low-fiber diet for at least 3 days, split preparation, and colonoscopy within 5 h allowed a CS rate above 90% and should always be encouraged. A 1-L PEG-ASC preparation was also associated with greater high-quality cleansing of the right colon and may be preferred.

Very low-volume bowel preparation (BP) for colonoscopy with 1-liter polyethylene glycol plus ascorbate (1L-PEG-Asc) has displayed high tolerability and quality of bowel cleansing. Concerns have been raised regarding its safety. We aimed to evaluate the incidence of adverse events (AEs) following BP with 1L-PEG-Asc or 2L-PEG-Asc.

From January 2019 to September 2020, data from all consecutive adult outpatients who underwent colonoscopy in Our Unit were collected. AEs were assessed by reviewing the clinical and laboratory data of patients who attended the Emergency Department (ED) of Modena District Hospitals in the 7 days following the colonoscopy, and were classified as "BP-related" or "BP-unrelated".

During the study, 4069 (68.03%) and 1912 (31.97%) patients underwent colonoscopy after taking 2L-PEG-Asc or 1L-PEG-Asc, respectively. Regarding AEs, 77 (1.29%) patients attended ED, 53 (53/4069, 1.30%) and 24 (24/1912, 1.25%) after taking 2L-PEG-Asc and 1L-PEG-Asc. BP-related AEs were observed in 5 (5/4069, 0.12%) and 4 (4/1912, 0.21%) patients, respectively. The most frequent BP-related AEs were tachyarrhythmias (6/5981, 0.10%).

The incidence rate of clinically relevant BP-related AEs is extremely low. This strongly suggests that 1L-PEG-Asc colonoscopy BP is as safe as 2L-PEG-Asc BP in a real-life clinical setting of unselected patients.

In colonoscopy, good bowel preparation is an important factor in determining the quality of colonoscopy. However, an increase in residual gastric volume (RGV) can lead to a higher risk of aspiration pneumonia. Therefore, the purpose of this study was to investigate the factors related to an increase in RGV with the usage of 1L polyethylene glycol (PEG).

We prospectively analyzed 268 patients who underwent both gastroscopy and colonoscopy at 2 hospitals from May to October 2021. Bowel preparation was performed using 1L in 127 patients (47.4%) and 2L PEG in 141 patients (52.6%). We investigated the time taken for bowel preparation solutions, the last water intake, total water intake, and RGV, and conducted a survey on taking compliance and satisfaction.

The level of RGV was significantly increased in the 1L PEG group when compared to the 2L PEG group (1L, 52.26 ± 65.33 vs 2L, 23.55 ± 22.99; P < .001). There was no difference between the 2 groups in the degree of bowel preparation, but there were more bubbles formed in the 1L group (1L, 1.91 ± 2.74 vs 2L, 1.10 ± 2.02; P = .007). In the case of RGV ≥ 50 mL, in multivariate analysis, the risk was higher in water intake within 5 hours and the patients who think the dose is too high (all P < .05).

Therefore, since RGV is higher in 1L PEG than in 2L PEG, it is necessary to be careful not to take water for at least 5 hours before the test.

Adequate bowel cleansing is essential for high-quality colonoscopy. Recently, a new very low-volume 1 litre (1L) polyethylene glycol (PEG) plus ascorbate solution (ASC) has been introduced. Our aims were to assess the effectiveness and tolerability of this product compared to low-volume 2L PEG-ASC and high-volume 4L PEG solutions, in a real-life setting. In six endoscopy units in Sweden, outpatients undergoing colonoscopy were either prescribed solutions according to local routines, or the very low-volume solution in split dose regimen. Bowel cleansing effectiveness and patient experience was assessed using the Boston Bowel preparation scale (BBPS) and a patient questionnaire. A total of 1098 patients (mean age 58 years, 52% women) were included. All subsegment and the total BBPS scores were significantly greater for 1L PEG-ASC in comparison to other solutions (p < 0.05 for 1L PEG-ASC and 4L PEG for transverse and left colon, otherwise p < 0.001). Nausea was more frequent with 1L PEG-ASC compared to 2L PEG-ASC (p < 0.001) and vomiting were more often reported compared to both other solutions (p < 0.01 and p < 0.05 for 2L PEG-ASC and 4L PEG, respectively). Smell, taste, and total experience was better for 1L PEG-ASC compared to 4L PEG (p < 0.001), and similar compared to the 2L PEG-ASC. In conclusion, 1L PEG-ASC leads to better bowel cleansing compared to 2L PEG-ASC or 4L PEG products, with similar or greater patient satisfaction.

The right colon is difficult to cleanse compared with other colon segments. This post hoc analysis of two randomised clinical trials (MORA and NOCT) examined whether 1L polyethylene glycol (PEG) NER1006 and two mid-volume alternatives could improve adequate and high-quality cleansing in the right colon among patients with complete cleansing assessments.

Patients received NER1006 (N2D), 2L PEG plus ascorbate (2LPEG) or oral sulphate solution (OSS) as a 2-day evening/morning split-dosing regimen or NER1006 as a same-day morning-only dosing regimen (N1D). Patients had full segmental scoring assigned by treatment-blinded central readers using the Harefield Cleansing Scale. The right colon adequate (score ≥ 2) and high-quality (score ≥ 3) cleansing success of NER1006 (N2D and N1D) versus 2LPEG and OSS was analysed individually and as pooled groups (N2D vs. 2LPEG/OSS). We assessed the comparative right colon cleansing rates of the N2D versus 2LPEG/OSS in overweight males. We also performed a multivariable regression analysis to examine factors affecting cleansing in the right colon.

A total of 1307 patients were included. Pooled N2D showed significantly improved rates of adequate-level cleansing in the right colon compared with 2LPEG (97.5% [504/517] vs. 94.6% [246/260]; p = 0.020) and OSS (97.5% [504/517] vs. 93.8% [244/260]; p = 0.006). In MORA, the rate of adequate right colon cleansing did not significantly differ between N1D and 2LPEG (95.2% [257/270] vs. 94.6% [246/260]; p = 0.383). The rate of right colon high-quality cleansing was significantly improved with N2D or N1D vs. 2LPEG (p < 0.001 for both), and was numerically higher with N2D versus OSS (p = 0.11). In overweight males, NER1006 delivered numerically higher adequate (p = 0.398) and superior high-quality (p = 0.024) cleansing rates versus 2LPEG/OSS. Multivariable regression analysis showed NER1006 was associated with adequate and high-quality cleansing (p = 0.031 and p < 0.001), while time between preparation and colonoscopy was negatively associated (p = 0.034 and p = 0.006).

NER1006 delivered improved rates of adequate and high-quality right colon cleansing compared with 2LPEG and OSS. The increased rate of high-quality cleansing with NER1006 versus its comparators was also seen in overweight males.

The incidence of colorectal cancer (CRC) is characterized by rapid declines in the wake of widespread screening. Colonoscopy is the gold standard for CRC screening, but its accuracy is related to high quality of bowel preparation (BP). In this review, we aimed to summarized the current strategy to increase bowel cleansing before colonoscopy. Newly bowel cleansing agents were developed with the same efficacy of previous agent but requiring less amount of liquid to improve patients' acceptability. The role of the diet before colonoscopy was also changed, as well the contribution of educational intervention and the use of adjunctive drugs to improve patients' tolerance and/or quality of BP. The review also described BP in special situations, as lower gastrointestinal bleeding, elderly people, patients with chronic kidney disease, patients with inflammatory bowel disease, patients with congestive heart failure, inpatient, patient with previous bowel resection, pregnant/lactating patients. The review underlined the quality of BP should be described using a validate scale in colonoscopy report and it explored the available scales. Finally, the review explored the possible contribution of bowel cleansing in post-colonoscopy syndrome that can be related by a transient alteration of gut microbiota. Moreover, the study underlined several points needed to further investigations.

Inpatient endoscopy delay (IED) negatively impacts the delivery of high-quality care. We aimed to identify factors associated with IED and evaluate its effect on hospital length-of-stay (LOS) and readmission.

This was a retrospective analysis of all inpatient endoscopies performed between November 2017 and November 2019 at a tertiary care center. IED was defined as the number of days elapsed between anticipated versus actual procedure day. Data were extracted from the endoscopy documentation software and via electronic chart review. Multivariate logistic regressions were modeled to determine variables associated with IED and hospital readmission.

A total of 4239 inpatients (mean age, 58.3 years; 50.3% women) underwent endoscopic procedures during the study period of which 819 patients (19.3%) experienced a delay. IED resulted in a median prolonged LOS of 2 days (interquartile range, 1-2 days). Patients with IED were less likely to have an etiology identified on endoscopy (odds ratio [OR], 0.73; 95% confidence interval [CI], 0.63-0.86; P < .001). The 2 most common causes for delays were poor bowel preparation (n = 218; 27%) and lack of endoscopy personnel/unit availability (n = 197; 24.4%). Independent predictors of IED included: older age (OR, 1.1; 95% CI, 1.01-1.03; P = .03), female sex (OR, 1.20; 95% CI, 1.03-1.40; P = .02), use of antithrombotics (OR, 1.30; 95% CI, 1.08-1.57; P = .006), opioids (OR, 1.23; 95% CI, 1.04-1.44; P = .012), being on contact isolation (OR, 1.38; 95% CI, 1.09-1.75; P = .008), and colonoscopy (OR, 1.50; 95% CI, 1.27-1.77; P < .001). Conversely, inpatients admitted to a dedicated GI medicine service were less likely to have IED (OR, 0.79; 95% CI, 0.65-0.96; P = .02). IED was the only independent predictor of 30-day readmission (OR, 1.22; 95% CI, 1.02-1.47; P = .03).

IED occurred frequently, unfavorably prolonged LOS, and was an independent risk factor for 30-day readmission. We provide a comprehensive analysis of actionable variables associated with IED that can be targeted to improve inpatient endoscopy delivery.

The effectiveness of bowel cleansing is a key element for high-quality colonoscopy. Recently, a 1 L polyethylene glycol plus ascorbate (PEG-ASC) solution has been introduced, but effectiveness and safety of this preparation have not been assessed in IBD patients. This study aims to evaluate effectiveness and safety of 1 L PEG-ASC solution in patients with IBD compared to controls.

We retrospectively analysed prospectively collected data on a cohort of 411 patients performing a colonoscopy after preparation with 1 L PEG-ASC, consecutively enrolled in 5 Italian centres.

Overall, 185/411 (45%) were patients with IBD and 226/411 (55%) served as controls. A significantly higher cleansing success was achieved in IBD patients (92.9% vs 85.4%, p = 0.02). The multiple regression model showed that presence of IBD (OR=2.514, 95%CI=1.165-5.426; P = 0.019), lower age (OR=0.981, 95%CI=0.967-0.996; P = 0.014), split preparation (OR=2.430, 95%CI=1.076-5.492; P = 0.033), absence of diabetes (OR=2.848, 95%CI=1.228-6.605; P = 0.015), and of chronic constipation (OR=3.350, 95%CI=1.429-7.852; P = 0.005), were independently associated with cleansing success. The number of treatment-emergent adverse events (TEAEs) (51 vs 62%, p = 0.821), and of patients with TEAEs (22.2% vs 21.2%, p = 0.821), were similar in IBD patients and in controls, respectively.

Results from this study support the effectiveness and safety of 1 L PEG-ASC solution in IBD patients, which may improve the definition of endoscopic outcomes both in Crohn's disease and ulcerative colitis.