Recommendations for fasting intervals prior to anesthesia in pediatric patients have changed in recent years. There are few data concerning infants less than 1 yr of age fed clear liquids or breast milk before surgery. We performed a prospective, blinded study to determine residual gastric volumes and pH in this population. Approximately 2 h prior to surgery, 46 formula-fed infants ingested up to 8 oz of clear liquids and 24 breast-fed infants nursed as usual. After induction of general anesthesia and tracheal intubation, gastric fluid samples were aspirated by a blinded researcher who measured gastric volume and pH. Sufficient gastric fluid for analysis was obtained from 10 (22%) of the infants fed clear liquids and 8 (33%) of the breast-fed infants. For the group fed clear liquids, the residual gastric volume was 0.3 +/- 0.9 mL/kg and the pH was 2.1 +/- 1.4. Eight (17%) had gastric volumes > or = 0.4 mL/kg, 2 (4%) had gastric volumes > or = 1 mL/kg, and 9 (90%) of 10 measured had pH < or = 2.5. In the breast-fed group the residual gastric volume was 0.71 +/- 1.1 mL/kg (P = not significant [NS]) and the pH was 2.6 +/- 1 (P = NS). All eight (33%) breast-fed infants had gastric volumes > or = 0.4 mL/kg (P = NS), seven (29%) had gastric volumes > or = 1 mL/kg (P = 0.03), and four (50%) of eight measured had pH < or = 2.5 (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)