The role of H2 receptor antagonist premedication in pregnant day care patients

Abstract

In a randomised study of 132 pregnant outpatients, the effect on gastric volume and pH of oral premedication with a single dose of an H2 antagonist was investigated. Either cimetidine 400 mg (n = 33), or ranitidine 150 mg (n = 33), were given 90 to 120 minutes before scheduled surgery. Mean pH was significantly higher in cimetidine (5.0) and ranitidine (5.2) groups, and mean volume was significantly lower in cimetidine (13.2 ml) and ranitidine (11.1 ml) groups compared with 66 untreated patients (pH 1.6, volume 22.1 ml). A gastric pH ≤2.5 was found in 97 per cent of unpremedicated patients and 35 per cent of these patients also had a gastric volume ≥ 25 ml. Eighty-three per cent of patients received their premedication within 75-200 minutes of surgery. Patients premedicated within that range had a significantly lower incidence of either a gastric pH ≤ 2.5 or a volume ≥ 25 ml (p < 0.01). Both cimetidine and ranitidine significantly reduced the number of patients with these risk-factors. Four patients, however, in the cimetidine group had both a pH ≤2.5 and a volume ≥ 25 ml. Pharmacological manipulation of the gastric environment does not prevent aspiration and clearly cannot be substituted for careful airway management and vigilance on the part of the anaesthetist. However, premedication of pregnant outpatients with a single, oral dose of an H2 antagonist is a simple, inexpensive, safe and effective way of reducing the risk of a severe aspiration pneumonitis. © 1985 Canadian Anesthesiologists.