Along with the trend of increasing incidence of colorectal cancer (CRC) and the launch of a population-screening program, colonoscopy has become one of the most common and important procedures in gastrointestinal endoscopy, not only in many developed countries, but also in Taiwan. According to an unofficial estimate, at present, nearly 160,000 colonoscopies are performed in Taiwan annually, including procedures performed for diagnostic, therapeutic, and screening purposes. Previous studies have shown that colonoscopy and polypectomy could effectively reduce both the incidence of and mortality from CRC; however, a growing body of evidence also suggests that substandard quality may decrease the effectiveness of colonoscopy [1] .

Bowel preparation is a key step in a successful and high-quality colonoscopy. Although there remains a lack of direct evidence establishing an association between the level of bowel preparation and future risk of interval cancer, previous large-scale studies have shown that suboptimal bowel preparation might lead to a longer procedure time, lower rate of cecal intubation, lower diagnostic yield, and higher risk of complications. All of these factors may influence the effectiveness of the screening program [2]  ;  [3] . Although failed cecal intubation with missed neoplasm is probably the most important factor related to the occurrence of proximal interval cancers, suboptimal bowel preparation may also play an important role. Our previous study showed that patients with better bowel cleansing prior to colonoscopy had not only a higher rate of detection of any kind of neoplastic lesion, but also a higher rate of detection of clinically important advanced neoplasms in the proximal colon [4] . Nevertheless, a recent Dutch study has shown that bowel preparation was experienced by patients undergoing colonoscopy for positive fecal immunochemical testing (FIT test) as the most burdensome aspect of this procedure, and the aspect causing the most suffering [5] . Moreover, failed bowel preparation increases the need for repeat examination, which may further burden the already overstretched capacity and limited resources in endoscopy. It is therefore crucial to seek a way to achieve effective bowel preparation with minimal burden to the examinees.

Over the past decades, there have been significant advances in the medications used for bowel cleansing before colonoscopy. Polyethylene glycol electrolyte lavage solution (PEG-ELS) and sodium phosphate (NaP) are currently the most widely used cleansing agents, and have greatly improved the cleansing effect. Nevertheless, there still exist a substantial number of patients with suboptimal bowel preparation at colonoscopy. Increasing numbers of studies have demonstrated that the quality of bowel preparation, especially in the ascending colon and cecum, is closely associated with the length of time between completion of preparation and the examination. Either a spilt-dose regimen or a same-day regimen is superior to a previous-evening regimen in terms of the level of bowel cleansing as well as diagnostic yields. In short, successful bowel preparation depends on the interval between the start time of ingestion of purgatives and the examination.

In this issue of the journal, an observational study by Kang et al demonstrated that changes in bowel-cleansing schedule significantly improved the cleansing and diagnostic yields in a screening setting. This study corroborates findings in our previous randomized trial demonstrating the usefulness and necessity of changing the current practice of previous-day bowel preparation and its significant impact on the important clinical outcome measure (i.e., cleansing effect and adenoma detection) [4] . Our study has demonstrated that colon preparation was better (93% vs. 72%) and more lesions were detected (2.8 vs. 1.9) in the group that underwent same-day bowel cleansing (2 L PEG-ELS) than in the group that underwent cleansing the evening before examination. A recent Korean study demonstrated that a preparation-to-colonoscopy time of around 3–5 hours had the best bowel-preparation quality [6] . Accordingly, a bowel-preparation schedule tailored for morning or afternoon colonoscopy is mandatory in clinical practice.

Patient perspective is also an important aspect that should be taken into consideration. Patient acceptance of ingesting purgatives in the morning for afternoon colonoscopy should not present a problem, but it is questionable whether examinees are willing to awaken early for bowel preparation. Unger at el reported in their survey that as many as 85% of patients who were undergoing colonoscopy stated they would be willing to get up during the night to take the morning dose of preparation [7] . In a recent survey in National Taiwan University Hospital, more than 90% of the Taipei residents undergoing screening colonoscopy stated that they are willing to accept an early-morning bowel preparation for morning colonoscopy after being given instructions on the potential advantages of such a preparation schedule. Thus, concerns about patient willingness should not be a deterrent to prescribing split-dose preparations for colonoscopy.

Unfortunately, policies regarding the administration of anesthesia may present the main obstacle to such a practice. Many anesthesiologists are reluctant to provide sedation unless the patient has fasted for more than 8 hours; current guidelines allow intake of clear liquids not less than 2 hours before elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia. Huffman et al demonstrated that the mean volume of residual gastric contents of patients receiving split-dose bowel preparation was not different from that of patients receiving bowel preparation the evening before the procedure. Thus, the risk of aspiration should be similar in split-dose and previous-day bowel preparation [8] . A dialogue between the endoscopist and the anesthesiologist is thus necessary to eliminate any conflict regarding the timing of bowel preparation.

For the Asian population, who have a relatively lower body mass index, a 2-L same-day regimen of PEG-ELS rather than a 4-L split regimen is sufficient to achieve good bowel preparation. In this population, a 4-L regimen may decrease compliance because of increased discomfort contributing to a generally unfavorable experience. Such patients may be unwilling to undergo future colonoscopy either for screening or for surveillance. A recent randomized controlled trial in a Caucasian population has shown that 2 L of PEG-ELS could be as effective as a 4-L regimen with better tolerability and acceptability [9]  ;  [10] . This recommendation regarding timing is also applicable to NaP, but it is important to mention that the use of NaP has decreased recently in the USA because of the rare occurrence of renal damage from tubular deposition of calcium phosphate [11]  ;  [12] . This potential risk can be avoided by aggressive hydration and avoidance of NaP in older individuals, in those with, diabetes, hypertension, or cardiovascular disease, or in those taking certain medications (diuretics, renin-angiotensin inhibitors, or nonsteroidal anti-inflammatory drugs). Recent European and US guidelines therefore do not recommend NaP as a first-line bowel-cleansing agent [13]  ;  [14] .

In summary, changing a prescribing habit in clinical practice is not easy, and sometimes there are unexpected obstacles. Nevertheless, changing the timing of bowel cleansing is an effective way to improve the quality of the preparation, and does not increase the cost. It is the time for us to make such a change.

Conflicts of interest

The author declares no conflicts of interest.


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