Should we inhibit gastric acid secretion before cardiac surgery?

Stress can decrease intragastric pH and cause erosion of gastric mucosa. Because cardiac surgery and cardiopulmonary bypass represent a major stress, the effects on intragastric pH of an H2-receptor antagonist, ranitidine, and an M1-muscarinic antagonist, pirenzepine, were evaluated. Intragastric pH was measured throughout elective cardiac surgery in 60 patients by a digital pH-meter during fentanyl-diazepam-nitrous oxide (50%) anesthesia. The gastric content was sampled at closure of the chest for bacterial count. Oral preoperative medication given randomly included (n = 20 in each group) 0.3 mg/kg diazepam 1 h before induction (group 1); diazepam plus ranitidine (150 mg) 1 h before induction (group 2); and diazepam plus pirenzepine (50 mg) on the evening before surgery and 1 h before induction of anesthesia (group 3). At induction intragastric pH was higher in group 2 (mean +/- SD = 7.42 +/- 1.07) than in group 1 (5.28 +/- 2.14) (P less than 0.01) but was not significantly different in group 3 (5.78 +/- 1.89) than in group 1. In no group did intragastric pH change significantly during surgery. Gastric juice was sterile in 92% of group 1, in 25% of group 2, and in 71% of group 3 patients (P less than 0.01). Postoperatively no gastrointestinal complications occurred, but there was a trend toward more patients developing nosocomial pneumonias in groups 2 and 3 (15%) than in group 1 (0%) (P = 0.06). Intraoperative intragastric pH is relatively high after diazepam premedication, thus the preoperative addition of ranitidine or pirenzepine would not be necessary and may possibly be hazardous.