Pharmacologic reduction of the risk of aspiration.

Parameters for significant risk of aspiration have been defined as a gastric pH less than 2.5 and/or a volume greater than 25 ml. We investigated the effects of metoclopramide and cimetidine, alone and in combination, on the pH and volume of gastric contents of patients taking nothing by mouth before general anesthesia. We divided 40 young women having gynecologic surgery into four groups: control subjects (group 1), those given metoclopramide (group 2), those given cimetidine (group 3), and those given both drugs (group 4). Injections were given 45 to 90 minutes before induction of general anesthesia, and no other premedicant was allowed. When the mean pH and volume of gastric contents were measured, the patients given both drugs had a mean pH of 6.9 and a mean volume of 2.0 ml. The control group showed significant risk for aspiration in terms of both volume and pH. Use of metoclopramide alone reduced the risk related to volume, and cimetidine alone reduced the risk related to pH. The most striking effects were achieved by the combination of the two agents, which produced a relatively narrow range of "safe" pH and volume.