Safety of Large-Volume, Same-Day Oral Bowel Preparations During Deep Sedation: A Prospective Observational Study

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Colonoscopy quality is directly related to the bowel preparation. It is well established that bowel preparations are improved when at least part of the laxative is ingested on the day of the procedure. However, there is concern that this can result in higher gastric residual volumes (GRV) and increase the risk of pulmonary aspiration. The aim of this study is to evaluate GRV and gastric pH in patients who received day-before bowel preparation versus those ingesting their laxative on the day of colonoscopy under anesthesiologist-directed propofol deep sedation.


This is a prospective observational study for patients undergoing same-day upper endoscopy and colonoscopy. All included patients had large-volume polyethylene glycol lavage preparation and received propofol sedation. Gastric fluid was collected during the upper endoscopy for volume and pH measurement.


The study included 428 patients with 56% receiving same-day laxative preparation and the remainder evening-before preparation. Mean ± SD GRV was 18.1 ± 10.2 mL, 16.3 ± 16.5 mL in each of these preparation groups, respectively (P = .69). GRV ≥ 25 mL or higher than expected GRV adjusted by weight (0.4 mL/kg) were also not different among the study groups (P = .90 and P = .87, respectively). Evaluating GRV based on time since last ingestion of preparation (3–5, 5–7, >7 hours) did not result in any differences (P = .56). Gastric pH was also similar between the bowel preparation groups (P = .23), with mean ± SD of 2.5 ± 1.4 for evening-before and 2.5 ± 1.3 for the same-day preparation. There were more inadequate bowel preparations in day before bowel preparations (P = .001).


A large-volume bowel preparation regimen finished on the day of colonoscopy as close as 3 hours before the procedure results in no increase in GRV or decrease in gastric pH.

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