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The preoperative fast is often an unpleasant preoperative experience that might be alleviated by allowing children to drink clear liquids. The authors compared gastric fluid volume and pH in two groups of children, one of whom was permitted clear liquids until 2 h before surgery (study group) and th

The effects on gastric fluid pH of a single dose of milk of magnesia given at various intervals prior to induction of general anesthesia in 115 parturients needing emergency operative delivery with general anesthesia were studied. In addition, the responses of rat lungs to tracheally injected gastric contents from parturients treated with orally administered milk of magnesia and untreated were compared. Stomach contents from parturients were removed by orogastric sump tube as soon as possible after induction of anesthesia. Single doses of milk of magnesia were given at various intervals prior to induction to 99 patients. No patient who received milk of magnesia 10 to 80 min prior to sampling was found to have a gastric-fluid pH of less than 2.5 and volume of more than 25 ml. Five parturients who had taken milk of magnesia and had gastric-fluid pH values of less than 2.5 had received the antacid more than 80 min prior to sampling of gastric contents. Of 16 patients who did not receive an antacid, five had gastric-fluid pH values of less than 2.5 and volumes of more than 25 ml. Lung-weight-to-body-weight (LW/BW) ratios were significantly different for the three groups of rats studied. The LW/BW ratio was 8.0 x 10-3 for rats that received tracheal instillations of gastric fluid from one parturient who was not treated with milk of magnesia and whose gastric-fluid pH was 1.4. The LW/BW ratio was 6.4 x 10-3 in 20 rats that received intratracheal instillations of gastric fluid from one parturient who was treated with milk of magnesia and whose gastric-fluid pH was 8.7. The LW/BW ratio of sham-injected rats was 5.3 x 10-3. The authors conclude that milk of magnesia is an effective preinduction antacid in emergency obstetric anesthesia; that a single dose of 30 ml prior to induction will increase the pH values of gastric contents to more than 2.5 in all patients in the interval from 10 to 80 min after ingestion; and that milk of magnesia-neutralized gastric contents resulted in less severe induced aspiration pneumonitis in rats than did acidic gastric contents.

The effects of preanesthetic oral cimetidine on gastric fluid pH and volume were studied in 97 infants and children. A dose-response curve was constructed using doses of 2.5, 5.0, 7.5, and 10 mg/kg. The ED50 of cimetidine that produces pH values higher than 2.5 was 3.0 mg/kg, and the ED95 was 7.5 mg/kg. Cimetidine exponentially reduced the volume of gastric fluid. Cimetidine was most effective between one and four hours after oral administration. In children who are at high risk of pulmonary aspiration, we recommend that oral cimetidine, 7.5 mg/kg, be given 1-3 hours preoperatively in order to protect the lungs from the accidental aspiration of acidic gastric secretions.

Eighty-eight children (mean age 5.6 yr, range 1-14 yr) about to undergo elective outpatient surgery were randomly assigned to four groups. All children were given phenolsulfonphthalein (PSP) orally 2-3 h before the scheduled time of surgery as a marker dye to assess gastric emptying. Immediately after receiving PSP they were given: group A--liquids, up to 5 ml/kg + placebo (glucose water 0.2 ml/kg); group B--liquids, up to 5 ml/kg + ranitidine 2 mg/kg in glucose water 0.2 ml/kg; group C--placebo only; group D--ranitidine only. Gastric contents were aspirated after induction of anesthesia. Mean volume (range) in ml/kg of aspirated gastric fluid in each group was: group A--0.34 (0-1.0); group B--0.17 (0.07); group C--0.25 (0-1.1); group D--0.16 (0-0.6). The pH mean (range) value was: group A--1.83 (0.9-3.6); group B--4.76 (2.0-7.7); group C--2.10 (1.2-4.1); group D--3.97 (1.3-7.3). PSP could not be detected in the gastric samples from children in whom the ingestion-sampling interval was more than 2.25 h. In comparison with prolonged starvation, administration of oral liquids without ranitidine 2-3 h preoperatively did not produce a significant increase in mean volume of gastric aspirate, and there was no increase in the number of patients with gastric aspirate greater than 0.4 ml/kg. Administration of ranitidine with or without fluids resulted in a decrease in both volume and acidity of gastric contents.