Factors affecting the quality of bowel preparation for colonoscopy in hard-to-prepare patients: Evidence from the literature

Table 1 Recommendation for bowel preparation in specific clinical settings

Clinical scenario	Remarks
Hospitalization	PEG-based regimens should be considered first in any preparation strategy because they are more likely to achieve adequate bowel cleansing while maintaining an optimal patient safety profile[13,45,48]
	Furthermore, multiple, combined strategies (e.g., written educational material, nurse facilitation of the process, etc.) based on a case-by-case decision could influence the outcome[45,48]
	Although no specific product is strongly recommended for difficult-to-prepare patients, clinical evidence suggests that a 1-L PEG-ASC preparation may be preferred in hospitalized patients[22]
Elderly	A strategy that includes a low-fiber diet for an extended period of time, a split preparation regimen, and a colonoscopy within 5 h of the end of preparation may improve cleansing success rates in the elderly[57]
	A 1-L PEG preparation may be preferred for the elderly due to higher cleansing quality and higher compliance due to lower volume[56,57,77]
Obesity	ESGE recommends the use of high volume or low volume PEG-based regimens, as well as non-PEG-based agents that have been clinically validated for routine bowel preparation[13]
	For elective colonoscopy, split-dose bowel preparation (with or without the additional measures) should be used, as it has been linked to improved preparation quality[13]
Diabetes mellitus	Current US guidelines do not support assumption of lubiprostone or magnesium citrate, instead recommending a split-dose bowel cleansing regimen with no adjustments for DM patients[8]
Chronic constipation	ESGE does not recommend any specific bowel preparation in constipation patients[13]
Inflammatory bowel disease	Split dosage was associated with better cleansing regardless of preparation in some studies[106,108]
	1-L PEG-ASC is associate to higher cleansing success and good safety and should be preferred[107]
Liver cirrhosis	The use of 2-L PEG-ASC for colonoscopy in liver cirrhosis to be a safe option[114]
Chronic kidney disease	All oral laxatives should be used with caution in patients with pre-existing chronic renal failure and liaison with the renal team is advised in patients undergoing dialysis or with advanced chronic kidney disease[54,106]
	Individualized laxative selection is strongly recommended for patients at risk for hydroelectrolyte disturbances (moderate quality evidence)[13]
	Because of the risk of magnesium toxicity and acute phosphate nephropathy, magnesium-based preparations and sodium phosphate should be avoided in chronic kidney disease patients[54,120,121]
	Also, because high-volume PEG-based regimens are poorly tolerated, low-volume PEG (2-L) solutions with ascorbic acid (PEG-ASC) have been proposed to reduce the patient’s excessive fluid intake[122]
	According to ESGE guidelines, patients with severe renal insufficiency (creatinine clearance less than 30 mL/min) should be prepared with isotonic high volume PEG solutions, whereas low volume PEG plus adjuvants (e.g., 1L-, 2L-PEG-ASC, 1 L PEG plus citrate) or non-PEG regimens (e.g., MCSP or oral sulfate solution) are not advised[13]
Heart disease	Bowel preparation (particularly after administration of PEG-ELS solution) could worsen heart failure[129]
Polypharmacy	Most medications can be taken up until the day of the colonoscopy and are taken with a small sip of water[135]
	Some medications, such as diabetes medications or anticoagulants, may need to be adjusted due to decreased oral intake prior to the procedure[13]
	Oral iron should also be discontinued at least five days before the colonoscopy because it causes residual feces[135]
History of colorectal surgery	In a study of 120 patients with prior colorectal resection for colorectal cancer, a low-volume mixed preparation (15 mg bisacodyl plus 2-L PEG) was not inferior to a high-volume regimen (4-L PEG) for adequate bowel cleansing during surveillance colonoscopy[139]
	In patients who had previously undergone left colectomy vs right colectomy, the mixed low-volume regimen had a higher success rate and tolerability[139,146]
History of poor bowel preparation	Despite a lack of strong evidence from randomized controlled trials, the ESGE guidelines and some studies recommend repeating colonoscopy using same-day or the next day with additional bowel cleansing (e.g., 500 mL PEG plus ascorbate) or using enema as a salvage option in patients with inadequate bowel cleansing[73,149-152,156]
	The next bowel preparation regimen should be tailored to the potential causes of failure[13]

PEG-ASC: Polyethylene glycol plus ascorbate; MCSP: Magnesium citrate plus picosulphate; DM: Diabetes mellitus; ESGE: European Society of Gastrointestinal Endoscopy.