Measuring gastric volume by dye dilution.

The double sampling method for measuring gastric volumes is analysed mathematically. It is shown to cause magnification of randomly occurring analytical errors in dye concentration. The errors which arise in calculated gastric volume depend on extent of analytical error, concentration of dye initially placed in the stomach, repetition of analysis cycle, and ratio of volume of added dye to gastric volume. By starting with dye-free water and doubling the concentration of dye added in serial volume determinations the error in calculated volume is markedly reduced and no longer increases with successive measurements. These modifications reduce the limitations inherent in the method as originally described.