Use of cimetidine as an oral antacid in obstetric anesthesia.

The H2-receptor antagonist, cimetidine, was used instead of magnesium trisilicate BPC as routine antacid therapy before both elective and emergency obstetric anesthesia. Two trials of its efficacy in increasing intragastric pH and decreasing the volume of gastric contents in parturients are reported. In the first trial, 400 mg of cimetidine given orally to patients being delivered by elective cesarean section effectively decreased gastric acidity, providing induction of anesthesia occurred 90-150 min after its administration. Of 62 patients requiring emergency anesthesia during active labor and who had been treated with 200 mg of cimetidine orally at 2-h intervals, 80% had gastric contents with a pH higher than 2.5. Failure to decrease gastric acidity to this level was mainly due to anesthesia being required within 60 min of the loading dose, but it also was considered that inaccurate timing of repeat doses and possibly delay in uptake due to gastric stasis by narcotic analgesia played a part. In trial 2 the same cimetidine regimen plus a 15-ml oral dose of 0.3 M sodium citrate given 10 min before induction of anesthesia was studied. All 72 women delivered by elective cesarean section had a low volume of gastric contents with pH greater than 2.5. Only 4% of 135 patients requiring emergency anesthesia had gastric aspirates the pH of which was less than 2.5. The volume (97 +/- 8.4 ml) of gastric contents removed from the latter patients were considered to still pose a hazard at induction of general anesthesia. No maternal or infant side effects related to cimetidine therapy were noted.