Quality of Inpatient Bowel Preparation for Colonoscopy at an Academic Center: An Opportunity for Improvement

Colonoscopy currently is the principal diagnostic technique for most colonic diseases. For an optimal examination, the bowel requires “preparation” by clearing it of all fecal material. Consensus guidelines have identified inpatient status as an independent predictor of poor bowel preparation.(1-3) Hospitalized patients generally tend to be older and have more chronic disease.(4) These differences indicate that inpatients may warrant special considerations when preparing the bowel prior to colonoscopy. An understanding of the challenges is important, because inadequate bowel cleansing may lead to canceled procedures, overlooked lesions, increased procedural times (prolonged cecal intubation and withdrawal times), and potentially increased complication rates.(5,6)

Optimal bowel preparation should clear the colon of all fecal matter, should not cause damage to the mucosa, and should be easy to administer without adverse effects.(7) However, to date no bowel preparation has demonstrated all these characteristics. Polyethylene glycol (PEG) has become part of preferred colonoscopy preparation (inpatient as well as outpatient) worldwide. The standard of four liters of PEG beginning the day before the procedure has been found to be both safe and effective.(2,8) PEG has been safely used in patients with renal dysfunction, quiescent inflammatory bowel disease, and lower gastrointestinal hemorrhage, providing an advantage over other purgatives for many hospitalized patients with renal insufficiency, liver insufficiency, or heart failure.(8) However, because PEG relies on high-volume lavage, patients’ ability to tolerate it remains a significant issue: an estimated 5% to 25% of patients are unable to complete a PEG preparation.(2,9)

In response to the lack of studies about inpatient bowel preparation, we aimed to measure the quality of bowel preparation and explore variables affecting bowel preparation for hospitalized patients undergoing colonoscopy. We sought to identify subgroups of patients at higher risk for poor bowel preparation so as to focus strategies for improvement.

Methods

We report an observational study designed to look at variables affecting the quality of bowel preparation for inpatient colonoscopy. The study was conducted at Massachusetts General Hospital in Boston, Massachusetts, and was approved by the hospital’s Institutional Review Board.

All hospitalized patients undergoing colonoscopy were eligible to be included in the study. Electronic medical records were used to gather individual data points, which were logged in a study database. Exclusion criteria (Figure 1) included flexible sigmoidoscopies, cases performed outside of the endoscopy suite (e.g., in intensive care units or operating rooms), and patients who did not receive PEG prior to colonoscopy. Any procedure aborted for reasons other than poor bowel preparation also was excluded. Additionally, for patients who underwent colonoscopy more than once during the same hospitalization, we recorded only the preparation and outcomes from the first procedure to avoid adding confounding information from the second procedure. General demographic data (age, gender, race, and marital status) were collected, as well as the reason for inpatient gastroenterology consultation, and the indication for colonoscopy. We analyzed diet orders 24 hours prior to colonoscopy and grouped patients into fasting (NPO), clear liquids, or “other.” Information on narcotic medications also was collected, as were data on any laxative that patient had received within two days prior to colonoscopy (Table 1). The time between bowel preparation and colonoscopy was measured by the difference between the time stamp marking the start of PEG administration and the time stamp for the start of the colonoscopy.

Figure 1. Patient cohort methodology. ER, emergency room; ICU, intensive care unit;
OR, operating room.

The recommended preparation for inpatients was a diet of clear liquids beginning the afternoon prior to the procedure, followed by 10 mg of bisacodyl and 4 liters of PEG (Nulytely) in the evening. This protocol differed from our outpatient regimen at the time due to the shorter period of the clear liquid diet and the addition of bisacodyl. Additional PEG was given the morning of the examination if the floor nurses thought that the preparation was incomplete.

The primary study outcome was bowel preparation quality. Our center uses a modified version of the five-point Aronchick scale for bowel preparation grading, which divides bowel preparation quality into five grades: unsatisfactory, poor, fair, good, and excellent.(10) The colonoscopist’s assessment of quality was made after intra-examination cleansing and is a required element for a complete report. We dichotomized these descriptions as either “acceptable” (those rated as excellent or good) or “not acceptable” (those rated as fair, poor, or unsatisfactory).

Investigators collected data over a 10-month period. The initial sample included 377 consecutive patients undergoing inpatient colonoscopy (not including sigmoidoscopies and procedures performed outside the endoscopy unit); further application of exclusion criteria (Figure 1) yielded a final sample size of 335 patients. Thirty-eight endoscopists plus four fellows under their supervision performed colonoscopies during the study period.

We constructed both univariate and multivariable logistic regression models (dependent variables listed in Table 2) with bowel preparation quality as the outcome variable. Odds ratios and their confidence intervals were then generated. We considered p values of less than .05 as statistically significant. Investigators used STATA13 (StataCorp LP, College Station, Texas) for all calculations.

Results

We evaluated bowel preparation rates in our inpatient sample. The percentage of patients graded as “excellent” was 4% (n = 14), and those graded as “good” was 48% (n = 160) per the modified Aronchick scale, for a total of 52% (n = 176) acceptable preps. Of the remaining patients, 29% (n = 97) had a “fair” preparation, and 19% (n = 64) had a poor or otherwise unsatisfactory preparation, for a total of 48% unacceptable. A contemporaneous group of 7067 outpatient exams during the same time period scored 81% acceptable preparation (“good” or “excellent”), which we include as a reference point for physician use of the modified Aronchick scale. The patients were fundamentally different and not comparable, but these outpatient data demonstrate the expected preparation rate for performance of an accurate colonoscopy.

Gender was a significant variable (p = .02), with females presenting for colonoscopy with better quality bowel preparation [OR=1.785; 95% CI (1.105, 2.88)]. This was a significant variable despite adjustment for age, race, and marital status, which were not significant variables.

The indications for colonoscopy included hematochezia (43%), melena (23%), anemia (7%), diarrhea (7%), inflammatory bowel disease (3%), abdominal pain (10%), anticoagulation risk assessment (3%), and other (12%). Some patients had multiple indications recorded. Indication for colonoscopy was a significant variable when dichotomized by lower gastrointestinal bleeding (LGIB) vs. non-LGIB indications (p = .03). Objective measures of LGIB were defined as a visual or occult test confirmation of the presence of blood in stool. Patients with anemia who did not have direct evidence of blood in the stool were not included in this definition of LGIB. Statistical analysis further revealed that patients who had LGIB as a documented indication for colonoscopy were significantly more likely [OR=1.742; 95% CI (1.062, 2.857)] to have higher-quality bowel preparation. In our sample, LGIB was the most common indication (58%) for inpatient colonoscopy. There were insufficient cases to consider emergent cases separately.

The time interval between start of bowel preparation and start of colonoscopy was a strong predictor (multivariable p = .002) of bowel preparation quality (Figure 2). In an attempt to explore the time interval issue further, we dichotomized time interval as greater than 24 hours and less than or equal to 24 hours. In this case, time remained a statistically significant variable (multivariable p = .002), with shorter-interval patients prepping better [OR=2.114; 95% CI (1.328, 3.366)]. We also dichotomized time intervals into greater than 14 hours and less than or equal to 14 hours, which was found to be not statistically significant (multivariable p = .42).

Figure 2. Box plots of time intervals between initiation of both bowel preparation and colonoscopy grouped by bowel preparation quality.

Notably, prior studies have identified an ideal time interval between bowel preparation and start of procedure.(11,12) Although our data agree that shorter time intervals are better, we did not find statistical significance for high-quality bowel preparation when the interval is shortened to less than 14 hours. Our data indicated that the majority of patients (67.0%) started bowel preparation between 4:00 PM and midnight, with the bulk (41.0% of all patients) beginning between 6:00 PM and midnight. Additionally, in terms of colonoscopy start times, the majority of patients (63.3%) underwent colonoscopy in the afternoon (noon to 6:00 PM).

Discussion

Our results are consistent with published evidence suggesting that inpatients have poorer-quality bowel preparation than outpatients.(1-4,13) Hendry et al.(13) noted that the proportion of inpatients with “good” bowel preparation was only 64%, in contrast to 86% rates of acceptable outpatient bowel preparation. Inpatients experience a higher incidence of incomplete or repeat colonoscopy, are less adherent to preparation instructions, and are more often judged to have poor preparation quality.(4) Focusing on inpatients may have implications not just for colonoscopy outcomes but also for inpatient cost (by avoiding need for repeat colonoscopies).(14) Additionally, inpatient examinations, although often adequate for the immediate diagnostic purposes, may not be sufficient for polyp and colorectal cancer screening. CMS is considering rules that report and regulate the frequency of colonoscopy for screening purposes. These data suggest that inpatient colonoscopies may be adequate for diagnostic purposes, but they are not adequate to exclude small polyps or be included in a systematic colorectal cancer screening and prevention program.

Several factors have been proposed to explain this discrepancy between inpatient and outpatient bowel preparation. Hospitalized patients tend to be older, and this patient population has been found to have a higher incidence of poor colonic preparation.(15) Inpatients also are less mobile and have more chronic disease. Other contributory factors include bed rest, higher likelihood of constipation, and possible use of narcotics. Hospitalized patients also differ from outpatients in terms of indication for procedure. For inpatients, common indications include LGIB, weight loss, iron deficiency anemia, abnormal imaging, and chronic diarrhea, in contrast with outpatient colonoscopies, which are commonly performed for malignancy screening or to assess inflammatory bowel disease.

Some common predictors of poor bowel preparation (applicable to both inpatients and outpatients) include male gender; use of tricyclic antidepressants; later colonoscopy start time; procedural indication of constipation; and a history of stroke, cirrhosis or dementia.(16,17) Patients also cite the bowel preparatory solution itself as a major barrier to undergoing colonoscopy.(9,18-20) A history of diabetes, appendectomy, colorectal resection, or hysterectomy was an independent predictor of poor bowel preparation.(21) In contrast, patients undergoing colonoscopy for lower gastrointestinal bleeding had better results, perhaps because of the motivation of perceived urgency or the cathartic effect of blood.

As has been noted by other authors, our data also found the time interval between start of bowel preparation and start of colonoscopy to be a strongly significant variable affecting bowel preparation quality.(12, 22) This is a challenge for hospitalized patients, because this patient population rarely is admitted for the sole purpose of colonoscopy, and bowel preparation needs to compete with other planned inpatient investigations. Bowel preparation start time often is based on timing of consultation, indication for procedure, and the availability of endoscopy. Outpatient guidelines have recommended keeping the interval between the last dose of bowel preparation and colonoscopy as short as possible.(23) Although some have advocated for ingestion of all of PEG solution on the day of colonoscopy for an afternoon procedure, others recommend split dosing.(24-27) Some authors recommend that bowel preparations be given in the morning of the colonoscopy. It also is notable that right-sided colon cleansing has been found to be significantly better with morning preparation.(28)

Published literature suggests that laxatives (e.g., Senna), when used, may improve cleansing.(29) Other authors also have pointed to beneficial effects of adjunct laxative use with PEG preparations(30); however, our study did not find adjunct laxative use to be a significant variable affecting inpatient bowel preparation quality (multivariable p = .82). Additionally, evidence shows that a low-fiber diet the day before colonoscopy may improve preparation tolerability.(31) Park et al.(32) also showed that a low-residue diet was at least as good as a clear-liquid diet the day prior to colonoscopy. However, it is not always possible to provide hospitalized patients dietary modifications for an entire day prior to their procedure. Our study also did not find that diet had significant effect on bowel preparation quality (multivariable p = .94). Additional study is needed to determine an efficient and optimal preparation for inpatients undergoing colonoscopy.

Conclusion

Prior studies have found that compared with outpatients, hospitalized patients have more difficulty preparing for colonoscopy, because they are older, dependent on others for personal care assistance, and have more chronic disease. Although this study is limited by its observational design, our results underscore the notion that bowel preparation for inpatients remains a challenge. The impact of poor preparation includes the potential of overlooking dangerous colonic lesions and increased cost of care.(32) In our cohort, patients with LGIB and female patients were better prepared for colonoscopy, suggesting the need for more aggressive preparation regimens for certain inpatients.

Acknowledgement. The authors wish to acknowledge the contribution of Hui Zheng PhD, Assistant Professor, Biostatistics Center, Massachusetts General Hospital, Department of Medicine, Harvard Medical School.

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