Ph and residual gastric volume after mannitol preparation: A randomized controlled study comparing ingestion three versus six hours prior to the procedure

Renzo Feitosa Ruiz, Jose Jukemura, Paulo Roberto Arruda Alves, Marcos Lera Santos

Objective: The main objective of the study is to compare gastric volume and pH values after the ingestion of mannitol three hours versus six hours before a colonoscopy procedure.

Methods: This study is a parallel randomized controlled trial with a 1:1 allocation ratio, involving ambulatory patients scheduled to undergo a colonoscopy procedure, not having previous gastric surgeries, with an American Society of Anesthesiology risk of less than III, older than 18 years of age, and with a fasting period for solid food of over eight hours. All participants underwent a bowel preparation with mannitol, being randomized to start the preparation either three or six hours before the colonoscopy procedure. Outcomes of interest were pH and gastric residual volume.

Results: The study sample included 102 subjects with subjects in the three-hour group being significantly older than individuals in the six-hour group (59.73 (± 18.69) vs. 51.71 (± 20.46); p=0.041) and subjects in the six-hour group presented higher BMI than individuals in the three-hour group (28.55 (± 5.15) vs. 26.35 (± 5.78); p=0.046). When evaluating study outcomes adjusting for baseline imbalances in age and BMI, we found no statistically significant differences between the three and the six-hour arms. In a subgroup analysis among the subgroup of patients with Diabetes Mellitus, the six-hour arm presented a significantly higher gastric volume when compared to the three-hour arm (127 versus 43.4 and 116 versus 37.8), respectively.

Conclusion: Our results are in line with the notion that a three-hour fasting period is safe to prevent aspiration from gastric content during bowel preparation with mannitol. Considering that long fasting protocols may result in adverse outcomes such as dehydration and electrolyte imbalance, we provide evidence to support the practice of short fasting periods.