The effect of preoperative oral fluid and ranitidine on gastric fluid volume and pH

One hundred unpremedicated daycare patients were randomly assigned to one of four groups. Between two and three hours preoperatively all patients received either oral ranitidine 150 mg, or placebo, with bromosulphthalein (BSP) 50 mg in 10 ml water, immediately followed by either 150 ml water or no further fluid. The residual gastric volume (RGV) in the two placebo groups was significantly lower in patients given 150 ml water (20.6 +/- 14.1 ml) than in those who continued fasting (29.9 +/- 18.2 ml) (p less than 0.05). The RGV was further significantly decreased in the two ranitidine groups (10.0 +/- 8.8, 9.7 +/- 10.5 ml) compared with the two placebo groups (20.6 +/- 14.1, 29.9 +/- 18.9 ml) (p less than 0.01). Mean pH values were significantly higher in the two ranitidine groups (6.71 +/- 0.99; 6.31 +/- 1.81) than in the two placebo groups (2.05 +/- 1.41; 1.72 +/- 0.33) but were not significantly different in the fluid versus non-fluid groups. In patients who ingested 150 ml water there was no correlation between the premedication interval and either RGV or pH values. The extremely low percentage of the original BSP (less than 0.9 per cent) in the gastric fluid of these patients demonstrated that gastric emptying of the ingested water was virtually complete prior to surgery. The combination of RGV of 25 ml or more with pH less than 2.5 was present in 56 per cent of patients who had only a sip of water with placebo, in 28 per cent of those who received 150 ml water with placebo, and in only two per cent of those patients who received ranitidine.