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This study documented gastric pH and volume, and the number of patients at risk for acid aspiration of gastric contents, in a group of mothers undergoing emergency cesarean section under general anesthesia. Patients were randomized in a double-blind fashion to receive omeprazole 40 mg intravenously or placebo at the time of decision to proceed to cesarean section. In addition, all patients received 10 mg intravenous metoclopramide and 30 mL of 0.3 M sodium citrate. Aspiration of gastric contents was undertaken immediately after endotracheal intubation (PI) and before tracheal extubation (PE). Patients with both pH < 3.5 and volume >25 mL were deemed to be at risk of acid aspiration should regurgitation occur. Only cases where the study-drug-to-PI-aspiration interval was >30 min were evaluated. There were 282 patients in the study group and 259 in the control group. PI, 11 patients (4.25%; 95% confidence interval [CI] 1.79–6.71) were at risk in the control group compared with 4 (1.42%; 95% CI 0.04–2.8) in the study group (P = 0.045). The omeprazole-to-PI-aspiration interval in these four cases was ≤40 min. PE, 19 (7.3%; 95% CI 4.17–10.51) patients were at risk in the control group compared with 2 (0.7%; 95% CI 0–1.69) in the study group (P < 0.0001). Mean pH in patients receiving omeprazole was significantly higher (P < 0.001) than in the control group. Gastric volumes were significantly lower in the omeprazole group compared with the control group at both PI (P = 0.006) and PE (P = 0.01). Intravenous omeprazole 40 mg, given at the time of the decision to proceed to emergency cesarean section, reduces the risk of acid aspiration provided that at least 30 min has elapsed from drug injection.