Introduction

Colorectal screening is thought to lead to a decrease in death due to colorectal cancer [1]. Improvement and advances in endoscopic therapies such as polypectomy, endoscopic mucosal resection (EMR), and endoscopic submucosal dissection (ESD) enable us to resect precancerous lesions more safely and precisely [2–7]. However, poor bowel preparation remains one of the main problems associated with poor adenoma detection rate. Clinically, poor bowel preparation is detected in 20–25 % of all colonoscopies [8, 9]. The American Gastroenterological Association (AGA) guideline states that the choice of bowel preparation regimen should be based on cleansing efficacy first, and patient tolerance second, and one of the main reasons for poor patient tolerance was the large volume that patients needed to consume before colonoscopy [10].

Bowel preparation methods for colonoscopy are assessed based on their efficacy, safety, and tolerability. Polyethylene glycol (PEG) electrolyte lavage solution is widely regarded as the first-line bowel preparation worldwide. Regularly, PEG is available in a 4 L volume, and the use of a split-dose cleansing regimen is strongly recommended for elective colonoscopy [10]. On the other hand, a same-day regimen is an acceptable alternative to a split regimen, especially for patients undergoing an afternoon examination. In healthy individuals, a 4 L PEG regimen produces a bowel cleansing quality that is not superior to a 2 L low-volume PEG with ascorbic acid [11–15]. However, low-volume PEG is highly concentrated and it causes dehydration [16]. Thus, it is used with caution especially in the elderly and patients with renal dysfunction. In Japan, a low-volume PEG with ascorbic acid was marketed in 2012. However, the 2 L volume remains challenging for many patients. A same-day 1 L low-volume PEG method, with previous day low-residue diet and laxative, was introduced in our center to improve tolerability. In this study, we analyzed the efficacy and the safety of this method, especially for the elderly people and patients with renal dysfunction.

Methods

This was a single-center, retrospective study involving 5427 patients who undertook the same-day low-volume 1 L PEG (MoviPrep: Ajinomoto, Tokyo, Japan) method, and underwent colonoscopy in the afternoon at the Kyoto Prefectural University of Medicine from November 2014 to September 2015. Patients were also required to take a low-residue diet and 10 mL of sodium picosulfate in the evening of the day before colonoscopy. Then, patients took 1 L PEG and 0.5 L water 4 h before examination, which must be completed 2 h before the procedure. Patients were asked to drink as much water as possible just before the procedure. The amount of additional water was not set because it was dependent upon patients’ ability. With respect to low-residue diet, we used the regimen for low-residue diet as a special ready-made food from a pharmacy. There were various kinds of them, and patients could choose one of them according to their liking. A homemade liquid diet was used only for the patients who declined it. In cases of poor preparation before colonoscopy, an enema was added. For the enema, 300–500 mL of lukewarm water was used and it was performed 1–5 times depending upon the status of the feces. We didn’t use additional PEG. We included consecutive patients who were (1) more than 18 years old; (2) scheduled for total colonoscopy in the afternoon; and (3) underwent colonoscopic examination, polypectomy, and EMR for polyps ≤20 mm in size. We excluded (1) patients whose colonoscopy had not been recorded in detail; (2) cases with ESD because some ESD cases were performed in the morning, and they needed a much longer time than routine colonoscopy and EMR. All colonoscopy examinations were performed by 25 endoscopists who had performed at least 500 colonoscopies.

Patients were divided into three age groups as the non-elderly (18–64 years old), the elderly (65–79 years old), and the special-elderly (≥80 years old) groups. The clinical characteristics and colonoscopic outcomes including age, sex, body weight, reason of colonoscopy, number of enema, mean insertion time, mean procedure time, cleansing level, rate of sedation, pain during the procedure, and the rate of antithrombotic drugs were analyzed by reviewing the medical records. Cleansing level was evaluated with the Boston bowel preparation score (BBPS) during colonoscopy [17]. The total score of BBPS was categorized into three groups: 9, 6–9, and 0–5. BBPS ≥ 6 was defined as good preparation and BBPS 0–5 as poor preparation. Pain during the procedure was classified as weak, medium, and strong by each endoscopist.

With respect to the safety of a same-day low-volume 1 L PEG method, the patients in the special-elderly group who had blood tests both before colonoscopy and within 1 month after colonoscopy were examined for detailed characteristics, including age, sex, body weight, the prescription of some drugs (anti-diabetes mellitus drugs, antithrombotic drugs, diuretics, laxatives, antihypertensive medications). Completion of 1 L PEG, additional enema for poor preparation, and complications were analyzed. Additionally, the special-elderly with renal dysfunction, whose creatinine (CRE) value was ≥1.1 mg/dL, were tested for irreversible CRE elevation (≥0.5 mg/dL) at 1 month after colonoscopy. Moreover, factors for poor preparation (BBPS 0–5) were examined.

We also analyzed patients with renal dysfunction (CRE ≥ 1.1 mg/dL) among 5427 patients, including hemodialysis, in whom blood examinations before and 4–5 h after 1 L PEG intake were performed. The values of WBC, hematocrit, electrolytes (Na+, K+, Cl−), and CRE were examined.

All patients provided written informed consent to undergo colonoscopy. The ethics committee of the Kyoto Prefectural University of Medicine approved this study. This study was carried out in accordance with the World Medical Association Helsinki Declaration and was registered in the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) as Number UMIN000011269.

Colonoscopy Equipment

A normal length colonoscope with a single channel (EC-590MP and EC-L590ZP; Fujifilm Medical Co., Tokyo, Japan; PCF-Q260AZI, CF-HQ290, Olympus Medical Co., Tokyo, Japan) was used for all colonoscopic examinations. Most procedures were performed with air insufflation, though some cases were performed with CO2 insufflation [19]. In some cases, conscious sedation was performed, mostly with midazolam (2–10 mg), according to the patient’s request or pain status in previous procedures. Monitoring with an automatic blood pressure monitor was performed in all cases during sedation.

Statistical Analysis

Statistical analyses were performed using the Mann–Whitney U and the Chi-square tests (SPSS version 22.0 for windows, IBM Japan, Ltd., Tokyo, Japan). P value of <0.05 was considered statistically significant.

Results

Overall patient characteristics and colonoscopic results of all 5427 cases are given in Table 1. Mean age of all patients was 64.5 ± 13.8 years old, and 58.8 % (3189 cases) were male. Mean body weight was 56.5 ± 12.1 kg. Mean insertion time and procedure time were 10.1 ± 13.5 min and 28.2 ± 35.6 min, respectively. With respect to bowel preparation, 77.4 % (4202 cases), 18.5 % (1005 cases), and 4.1 % (320 cases) were classified as BBPS 9, 6–8, and 0–5, respectively. The number of patients receiving additional enemas was 491 (9.0 %). The rate of sedation was 13.8 % (748 cases). The rates of weak, medium, and severe pain were 79.7 % (4323 cases), 15.7 % (850 cases), and 4.6 % (254 cases), respectively.

Table 1 Overall patient characteristics and colonoscopic results for same-day low-volume 1 L PEG
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The comparisons between the non-elderly, the elderly, and the special-elderly groups are shown in Table 2. There was a significant difference in body weight between the non-elderly and special-elderly groups (59.3 ± 11.4 vs. 50.4 ± 11.9 kg, P < 0.001). There were also significant differences in mean insertion time between the non-elderly and special-elderly groups (9.9 ± 9.0 vs. 10.9 ± 8.0 min, P = 0.03). With respect to bowel preparation, the rates of good preparation (BBPS ≥ 6) in the non-elderly and special-elderly groups were 94.6 and 91.8 % (P = 0.002). The rates of BBPS 9 in the elderly and special-elderly groups were higher than the non-elderly group (20.7 vs. 24.6 %, P = 0.001, 20.2 vs. 24.6 %, P = 0.01). There were significant differences between the non-elderly, elderly, and special-elderly groups in terms of strong pain during colonoscopy (5.2 vs. 3.6 vs. 7.8 %, P = 0.006, P < 0.02). There was more antithrombotic drug use in the elderly and special-elderly groups than the non-elderly group (12.6 vs. 2.7 %, P < 0.001, 18.8 vs. 2.7 %, P < 0.001).

Table 2 Comparison between the non-elderly, elderly, and special-elderly groups in same-day low-volume 1 L PEG
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Detailed characteristics of the 256 patients in the special-elderly group who had blood tests before and after 1 L PEG are presented in Table 3. The rate of renal dysfunction was 15.2 %. Various kinds of drug were prescribed. The rate of antihypertensive medications was highest (54.6 %), followed by laxatives (25.0 %). With respect to bowel cleansing, completion of low-volume 1.0 L PEG was achieved in 96.5 % (251 cases) of patients and 9.8 % of cases needed an additional enema before colonoscopy. The rate of cases with good bowel preparation (BBPS ≥ 6) reached 92.6 %. The total complication rate was 3.2 %, with nausea, vomiting, hypertension, and coldness detected in 2.0, 0.4, 0.4, and 0.4 %, respectively. Besides these cases, there were no severe complications. No irreversible CRE elevation was detected after the procedures.

Table 3 Safety of same-day low-volume 1 L PEG for the special-elderly group
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Risk factors for poor preparation and colonoscopic results in the special-elderly group are described in Table 4. There were no significant differences in risk factors between the poor and good preparation groups. Regarding results of colonoscopy, the rate of strong pain was higher in the poor preparation group than in the good preparation group (26.3 vs. 2.6 %, P < 0.001).

Table 4 Risk factors for poor preparation and colonoscopic results of same-day low-volume 1 L PEG in the special-elderly group
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With respect to the safety in renal dysfunction, the details of 68 cases without hemodialysis and 25 cases with hemodialysis are shown in Table 5. In cases without hemodialysis, there were significant differences of hematocrit and CRE before and after prescription of low-volume 1 L PEG (hematocrit: 36.7 ± 6.1 vs. 39.0 ± 5.7, P = 0.006; CRE: 1.30 ± 0.12 vs. 1.37 ± 0.14, P = 0.04). On the other hand, there were no significant differences in cases with hemodialysis, except for CRE. Additionally, there were no serious symptoms among these 93 cases with renal dysfunction.

Table 5 Safety of same-day low-volume 1 L PEG for cases with renal dysfunction
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Discussion

The efficacy and safety of low-volume PEG has been evaluated in many reports. A randomized study in 307 patients showed successful colon cleansing was achieved in 90.6 % in the 2 L low-volume PEG group compared with 96 % in the 4 L PEG group (not significant) [11]. Additionally, complications were similar in these two groups. Another randomized study showed that overall an adequate bowel cleansing score was achieved in 81.6 % of the 2 L low-volume PEG and 80.0 % of the PEG + simethicone groups [12]. However, there were differences between excellent and good preparation rates between the two groups (low-volume PEG: 11.6 and 38.3 %; PEG + simethicone: 26.6 and 23.3 %, respectively). Other studies have also shown significant differences in the percentage of bowel wall visualization in favor of PEG + simethicone patients compared with low-volume PEG [14, 15]. In our study, the rates of good preparation (BBPS ≥ 6) were high (non-elderly: 94.6 %; elderly: 93.7 %; special-elderly: 91.8 %). The rates of excellent preparation (BBPS 9) were also high (non-elderly: 24.6 %; elderly: 20.7 %; special-elderly: 20.2 %). We conclude that a same-day 1 L low-volume PEG method is efficient for bowel preparation.

With respect to complications, one study showed no significant difference in 2 L low-volume PEG, apart from changes in bicarbonate blood concentrations [13]. Additionally, 1 severe adverse event (myocardial infarction) in the 2 L low-volume PEG group was detected. In our study, complications were examined in detail in the special-elderly group. The total complication rate was 3.2 %, with nausea, vomiting, hypertension, and coldness detected in 2.0, 0.4, 0.4, and 0.4 %, respectively. Additionally, renal dysfunction was detected in 15.2 % of the special-elderly, but there were no irreversible elevations of CRE among them. Patients with renal dysfunction were further analyzed in our study. Only an elevation of hematocrit was seen in the 68 cases with renal dysfunction. There were no significant changes after 1 L PEG intake in the 25 patients receiving hemodialysis. Thus, there were no serious symptoms among these 93 patients with renal dysfunction. The safety of a same-day 1 L low-volume PEG method was confirmed when it was examined in the special-elderly cases. We suggest that the reduced volume of PEG intake makes this method safer. However, low-volume PEG caused moderate elevation of hematocrit in patients with renal dysfunction. Thus, we have to pay attention to all patients with low-volume PEG regarding dehydration.

One study showed the acceptability rate was higher in 2 L low-volume PEG than 4 L PEG (83 vs. 76 %, respectively; P = 0.02) [18]. Another study showed the efficacy of a low-residue diet in decreasing the amount of PEG required [19]. Another study showed that 43 % of patients in the 4 L PEG group showed a good or excellent preparation compared with 23 % in the low-volume 2 L PEG plus sennosides group (P = 0.03) [20]. However, the low-volume PEG plus sennosides method was significantly better tolerated than standard PEG (P < 0.001). According to these reports, patients in our study were required to take a low-residue diet and 10 mL of sodium picosulfate in the evening of the day before low-volume PEG.

Regarding patient characteristics, older age and male sex were associated with inadequate preparation [21–23], as was higher body mass index (≥25) [21, 24]. Being an in-patient, diabetes mellitus, segmental colonic resection, and neurologic conditions related with poor mobility, such as stroke and Parkinson’s disease, were also associated with poor preparation [21, 23, 25, 26]. Our study showed sex, body weight, various drugs, including anti-diabetes mellitus drugs, were not risk factors for poor preparation in the special-elderly, though the rate of poor preparation was significantly higher in the special-elderly compared with the non-elderly.

Poor bowel preparation was definitely associated with missing polyps. A report showed adenomas and high-risk lesions were frequently detected on repeat colonoscopy in patients with inadequate bowel preparation, suggesting that these lesions were likely missed [27]. Recent reports have shown that narrow band imaging (NBI) and blue laser imaging (BLI) were efficient in improving polyp detection and polyp visibility [28, 29]. However, endoscopic views of NBI and BLI become reddish in poor preparation, and this reduces the merits of these modalities. Good preparation with good tolerability is expected to increase polyp detection. We propose that the same-day low-volume 1 L PEG method is a candidate for this.

Regarding the limitations of this study, it was a retrospective study and had only one arm of 1 L PEG method. Further controlled study is needed to analyze a detailed efficacy of this method. Our study was that it was only performed in our single Japanese center. Regularly, the mean body weight of our Japanese patients is lower than that of western people. Thus, our regimen may not work in the West. The evaluation of BBPS was performed by the 25 endoscopists subjectively and was not reviewed by other endoscopist, and the BBPS of each part of the colon was not examined. The safety of this method was analyzed only for the special-elderly people. Additionally, due to the fact that this was a retrospective study we are unable to get timely blood examinations for the special-elderly with renal dysfunction just after colonoscopy. We only analyzed the patients whom we knew had renal dysfunction. It had a kind of selection bias.

In conclusion, our study showed that the same-day low-volume 1 L PEG method was safe and effective as a bowel preparation for the elderly and patients with renal dysfunction. However, vigilance for the associated dehydration seen in some cases is advised. We think our 1 L PEG method can be applied for all patients receiving routine colonoscopy. It is especially useful for the people who weren’t able to complete the regular 2–4 L PEG method previously. Elderly people are also suitable for this method.