Bowel preparation before colonoscopy - ASGE

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    ww.giejournal.orgBowel preparation before colonoscopyThis is one of a series of documents discussing theuse of GI endoscopy in common clinical situations.The Standards of Practice Committee of the AmericanSociety for Gastrointestinal Endoscopy prepared thisdocument that updates a previously issued consensusstatement and a technology status evaluation reporton this topic.1,2 In preparing this guideline, a searchof the medical literature was performed by usingPubMed between January 1975 and March 2014 by us-ing the search terms colonoscopy, bowel prepara-tion, intestines, and preparation. Additionalreferences were obtained from the bibliographies ofthe identified articles and from recommendations ofexpert consultants. When limited or no data existfrom well-designed prospective trials, emphasis is givento results from large series and reports from recognizedexperts. Recommendations for appropriate use ofendoscopy are based on a critical review of the avail-able data and expert consensus at the time that thedocuments are drafted. Further controlled clinicalstudies may be needed to clarify aspects of recommen-dations contained in this document. This documentmay be revised as necessary to account for changesin technology, new data, or other aspects of clinicalpractice. The recommendations were based on re-viewed studies and were graded on the strength of thesupporting evidence (Table 1).3 The strength of individ-ual recommendations is based both on the aggregateevidence quality and an assessment of the anticipatedbenefits and harms. Weaker recommendations areindicated by phrases such as we suggest, whereasstronger recommendations are typically stated as werecommend.

    This guideline is intended to be an educational deviceto provide information that may assist endoscopists inproviding care to patients. It is not a rule and shouldnot be construed as establishing a legal standard ofcare or as encouraging, advocating, requiring, ordiscouraging any particular treatment. Clinical deci-sions in any particular case involve a complex analysisof the patients condition and available courses of action.Therefore, clinical considerations may lead an endoscop-ist to take a course of action that varies from these recom-mendations and suggestions.American Society for Gastrointestinal Endoscopy

    /j.gie.2014.09.048Colonoscopy is the current standard method for imag-ing the mucosa of the entire colon. Large-scale reviewshave shown rates of incomplete colonoscopy, defined asthe inability to achieve cecal intubation and mucosal visu-alization effectively,4,5 between 10% and 20%,4 well overtargets recommended by the U.S. Multi-Society Task Forceon Colorectal Cancer.6 The diagnostic accuracy and thera-peutic safety of colonoscopy depends, in part, on the qual-ity of the colonic cleansing or preparation.7 Inadequatebowel preparation can result in failed detection of preva-lent neoplastic lesions and has been linked to an increasedrisk of procedural adverse events.1,8 Sidhu et al9 performedan audit of all colonoscopies performed between April2005 and 2010 at the Royal Liverpool University. Ofthe 8910 colonoscopies performed, 693 were incomplete(7.8%; 58% women; mean age, 61 years), and inadequatebowel preparation was the most common reason for in-complete colonoscopy, accounting for nearly 25% of failedcolonoscopies in their series.

    Numerous investigations designed to identify predictorsof inadequate colonoscopy bowel preparation6-8 havefound that inadequate preparation is more common in pa-tients with the following characteristics: previous inade-quate bowel preparation, non-English speaking, Medicaidinsurance, single and/or inpatient status, polypharmacy(especially with constipating medications such as opiates),obesity, advanced age, male sex, and comorbidities suchas diabetes mellitus, stroke, dementia, and Parkinsonsdisease.1,10,11 Poor adherence to preparation instructions,erroneous timing of bowel purgative administration, andlonger appointment wait times for colonoscopy have alsobeen associated with poor bowel preparation.10,11 Thus,it is important for clinicians to understand the numerousmodifiable physician- and patient-related factors thatcan lead to colonoscopy failure to reduce its incidenceand provide patients with improved outcomes.

    The ideal preparation for colonoscopy should reliablyempty the colon of all fecal material in a rapid fashionwith no gross or histologic alteration of the colonic mu-cosa. The preparation should not cause patient discomfortor shifts in fluids or electrolytes. The preparation shouldbe safe, convenient, tolerable, and inexpensive.12 Unfortu-nately, none of the currently available preparations haveall of these characteristics. This document updates a previ-ous consensus document and a technology status evalua-tion report on bowel preparation1,2 and reviews theavailable evidence regarding bowel preparation beforecolonoscopy.Volume 81, No. 4 : 2015 GASTROINTESTINAL ENDOSCOPY 781

  • TABLE 1. GRADE system for rating the quality of evidence for guidelines

    Quality of evidence Definition Symbol

    High quality Further research is very unlikely to change ourconfidence in the estimate of effect


    Moderate quality Further research is likely to have an important impacton our confidence in the estimate of effect and maychange the estimate


    Low quality Further research is very likely to have an importantimpact on our confidence in the estimate of effectand is likely to change the estimate


    Very low quality Any estimate of effect is very uncertain 4BBB

    Adapted from Guyatt et al.3

    Bowel preparation before colonoscopyGENERAL CONSIDERATIONS

    It is important that patients are educated and engagedin the colonoscopy preparartion process,13 and it hasbeen shown that effective education significantly improvesthe quality of bowel preparation.14 Patient counselingalong with written instructions that are simple and easyto follow and in their native language should be providedto patients,15 and patient education may improve withthe use of visual aids.16 Recently, educational bookletswere shown to improve bowel preparation and quality in-dicators such as cecal intubation rates.17,18 Smartphone ap-plications have even been developed to guide patientsthrough the preparation process.19 Patients can also bedirected to resources such as the ASGE Website entitledUnderstanding Bowel Preparation ( that explain the stepsinvolved and importance of optimizing bowel preparationfor colonoscopy.

    Bowel preparation regimens typically incorporate die-tary modifications along with oral cathartics.20 Mostcommonly, a clear liquid diet is advised for the day beforecolonoscopy. Red liquids can be mistaken for blood in thecolon or can obscure mucosal details and should beavoided. Clear liquids can be taken up to 2 hours beforethe procedure.21 However, it is not clear whether a clearliquid diet the day before colonoscopy offers advantagesover a low-fiber diet in terms of preparation quality.22-25

    A low-residue diet that avoids foods containing seeds andother indigestible substances is often recommended forseveral days before the procedure and has been shownto be at least as effective as a clear liquid diet20,26 and asso-ciated with increased patient satisfaction.23

    Although the individual components of bowel prepara-tions vary widely, the combination of dietary restrictionand cathartics has proven to be safe and effective forcolonic cleansing for colonoscopy.27 In a study of hospital-ized patients undergoing colonoscopy, a clear liquid dietbefore administration of the bowel preparation was the782 GASTROINTESTINAL ENDOSCOPY Volume 81, No. 4 : 2015only dietary modification that improved the quality ofpreparation.28 Adequate hydration is an important ad-junct to any bowel preparation before colonoscopy.29

    Additional medication modifications may be required inspecial populations such as diabetic patients, who mustmaintain glycemic control, and patients taking anticoagula-tion agents.30TIMING OF PREPARATION

    Giving part (usually half) of the bowel preparationdose on the same day as the colonoscopy (termed split-dose) results in a higher-quality colonoscopy examinationcompared with ingestion of the entire preparation on theday or evening before colonoscopy.31-39 A higher-qualitybowel preparation due to this split-dose has been demon-strated to increase the adenoma detection rate.40 In addi-tion to a higher-quality bowel preparation, split-dosingalso improves patient tolerance, as demonstrated by anincreased willingness to repeat the procedure using thesame preparation in the future.37 Typically, the standarddose of a bowel preparation is split between the day beforeand the morning of the procedure. The timing of the sec-ond dose must allow sufficient time for the patient to com-plete the second dose, have the desired response, and forthe patient to travel to the center where the colonoscopywill be performed. The second dose should be adminis-tered between 3 to 8 hours before the planned start ofthe colonoscopy procedure.41,42 A prospective trial foundno difference in residual gastric fluid in patients usingsplit-dose bowel preparation and bowel preparation giventhe evening before colonoscopy.43 Patients must havecompleted the preparation at least 2 hours before sedationis given to avoid potential aspiration as recommended inthe American Society of Anesthesiologists (ASA) guide-lines.21 However, institutional policies may vary from thisASA recommendation. In patients with early morning ap-pointments, this second morning dose may


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