The effects of intravenous cimetidine and metoclopran ide on gastric pH and volume in outpatients

Study Objective: To evaluate and compare the preinduction effects of intravenously (IV) administered cimetidine alone and combined with metoclopramide on gastric contents and postoperative nausea and vomiting in outpatients undergoing elective surgery. Design: Patients were allocated randomly to 4 groups with 20 patients in each group. Setting: Ambulatory surgery at a university-affiliated city hospital. Patients: Eighty patients undergoing elective gynecologic or orthopedic procedures were studied. Interventions: Outpatients in Group 1 and inpatients in Group 2 served as controls. Outpatients in Group 3 received 300 mg of cimetidine, and outpatients in Group 4 received 300 mg of cimetidine and 10 mg of metoclopramide. All drugs were administered IV as an infusion over a 15-minute period, 30 to 45 minutes prior to induction of anesthesia. Measurements and Main Results: After induction of general anesthesia and endotracheal intubation, stomach contents were retrieved and volume and pH measured. Group 1 outpatients had a large residual gastric volume of 29.2 ± 15.9 ml, with a very low pH of 2.32 ± 1.23 and 15% frequency of postoperative vomiting. These patients are at high risk of developing significant pneumonitis in the event of the aspiration of gastric contents. The combination of cimetidine and metoclopramide in Group 4 provided the optimal, or safest, condition-i.e., high gastric pH [6.15 ± 0.71 (p < 0.005)] and low gastric volume [11.6 ± 7.37 ml (p < 0.001)], with no postoperative vomiting. Conclusions: The combination of cimetidine and metoclopramide given to ambulatory patients during the preinductive phase may prevent severe pulmonary consequences should aspiration occur and is more effective in this regard than cimetidine alone.