Determinants of liquid gastric emptying: comparisons between milk and isocalorically adjusted clear fluids.

BACKGROUND Although current preoperative fasting guidelines apply restrictions to drinks containing milk because of delayed gastric emptying, the safe volume of milk that can be consumed up to 2 h before surgery on a theoretical basis has not yet been defined. We aimed to determine whether delayed gastric emptying depended mainly on the total amount of calories irrespective of compositional differences between milk and clear fluids. METHODS We prepared five beverages with a uniform volume (500 ml) and step-wise increments in calories (0, 220, and 330 kcal), comprised mainly of non-human milk, pulpless orange juice, water, and gum syrup. The gastric emptying rate of each beverage was determined by ultrasound measurements of the gastric antral cross-sectional area after their ingestion by eight healthy fasting volunteers. RESULTS The emptying rates of 500 ml of orange juice and 330 ml of non-human milk with 170 ml of water (both were 220 kcal) from the stomach were similar. Furthermore, 450 ml of orange juice with 50 ml of gum syrup and 500 ml of non-human milk (both were 330 kcal) left the stomach at similar rates. The 220 kcal beverages emptied faster than the 330 kcal beverages. CONCLUSIONS There were no significant differences in liquid gastric emptying after drinking equal volumes of either orange juice or milk as long as both had the same amount of calories. Liquid gastric emptying depends chiefly on the total caloric content. CLINICAL TRIAL REGISTRATION UMIN000012537.