Background: Preoperative fasting of clear fluids is recommended to reduce the incidence of pulmonary aspiration under anesthesia but non-compliance may cause aspiration or an inconvenient delay in surgery. Safe reduction of fasting time below the current standard of 2 hours has been reported but has not been demonstrated clinically. The aim of this study was to determine if reducing the fast of clear fluids to 1 hour increases residual gastric volume.
Methods: 181 adult patients scheduled for gastroscopy at three sites were randomized to receive 200 ml of water either 80-150 (Standard Fast group) or 40-75 minutes (Short Fast group) before anesthesia. Patients were stratified to current proton pump and antacid therapy. Gastric contents were aspirated under vision by gastroscopy after induction of anesthesia and the volume and pH were compared between groups.
Results: Non-compliance with fasting time resulted in exclusion of 41 patients leaving 140 patients for analysis. The mean fasting times (mean ± SD) were 102 ± 20.5 min in the Standard Fast group and 56 ± 10.8 min in the Short Fast group. The proportions of patients receiving proton pump inhibitors were not different between groups (45.2% and 47.8% respectively, p=1.0). The gastric volumes and pH were similar (volume: 0.18 ml/kg ± 0.25 and 0.19 ml/kg ± 0.31, P=0.92; pH: 2.85 ± 2.02 and 3.10 2.48, P=0.61). There was no correlation between fasting time and gastric volume (r -0.03; p=0.72) or pH (r-0.02; p=0.84) and no difference in the proportion of participants with residual gastric volumes greater than 0.4 ml/kg.
Conclusions: In patients without risk factors for delayed gastric emptying, consumption of 200 ml of water up to 56 minutes before general anesthesia does not significantly affect gastric volume and pH compared with a longer fasting time of 102 minutes.