Preoperative oral fluids: is a five-hour fast justified prior to elective surgery?

The effects of preoperative oral administration of 150 ml fluid were studied prospectively in 140 unpremedicated, ambulatory outpatients presenting for first trimester therapeutic abortion. Intraoperative gastric fluid volume, pH, and rate of gastric emptying were measured in the four groups to which patients were randomly assigned. At an average time of 2 1/2 hr preoperatively all patients received either oral ranitidine, 150 mg, or a placebo tablet, with the nonabsorbable marker dye bromosulphthalein (BSP, 50 mg in 10 ml water, followed by either 150 ml water or no further fluid. The effect of volume ingested was assessed by comparing the volume of gastric contents obtained by gastric tube suctioning at the completion of surgery in the two groups given placebos. The gastric volume was significantly less in patients given 150 ml water (17.6 +/- 14.5) than in those given only BSP (26.7 +/- 18.9) (P less than 0.02), and was further significantly decreased in the two groups given ranitidine (8.3 +/- 7.3, 9.5 +/- 7.7 ml) (P less than 0.001). Mean pH values were significantly higher in the two ranitidine groups (5.52 +/- 1.79, 5.03 +/- 1.79) than in the two placebo groups (1.75 +/- 0.94, 1.92 +/- 1.27). The combination of a residual volume of 25 ml and pH less than 2.5 was found in 46% of patients given only BSP with placebo, in 23% of those given 150 ml water with placebo, and in no patient given ranitidine. There was no correlation between the gastric volume or pH values with the ingestion-surgery interval in patients given 150 ml water.