Comparison of the prophylactic use of magnesium trisilicate mixture B.P.C., sodium citrate mixture or cimetidine in obstetrics.

The effects of magnesium trisilicate mixture B.P.C., sodium citrate mixture or cimetidine on gastric pH and aspirated gastric volumes were compared in 78 obstetric patients during elective (a), or emergency (b) surgery. Magnesium trisilicate mixture B.P.C. was associated with the most alkaline values of gastric pH (mean (a) 7.9, (b) 7.3; range 2.9-9.1). Sodium citrate 0.3 mol litre-1 mixture resulted in the narrowest range of pH values of gastric contents (mean (a) 5.4, (b) 5.9; range 3.9-7.7). The ranges of aspirated gastric volumes were wide with both antacid regimens (magnesium trisilicate 12-172 ml, sodium citrate 9-290 ml). Cimetidine increased gastric pH to greater than 2.5 in 82% of patients (mean (a) 6.2, (b) 5.0; range 1.6-7.3), and was associated with significantly smaller volumes of aspirated gastric contents (range 0.5-44 ml). When gastric pH and volume were considered together, the groups of patients who received cimetidine were found to be closest to the defined "safe limits", of pH greater than 2.5 and volume less than 25 ml.