Objective: The non-invasive (13)C-octanoic acid breath test ((13)C-OABT) has recently been used to monitor gastric emptying. We evaluated (13)C-OABT as a method for assessing gastric emptying in relation to the amount of milk ingested in preterm neonates during their first days of life.
Methods: The (13)C-OABT was performed in 16 stable preterm neonates born between weeks 31 and 37 of gestation (mean +/- standard deviation: 34.0 +/- 1.5 wk). Birth weight was 1400 to 2680 g (2076 +/- 350 g); four newborns were small for gestational age. The newborns underwent (13)C-OABT three times according to the amount of (13)C-primed breast milk being fed to them (<7 mL/kg, 7-13 mL/kg, and 10-19 mL/kg per dose). (13)C-primed breast milk (the test meal) was prepared by adding (13)C-octanoic acid to pasteurized breast milk to achieve a concentration of 1 microL of (13)C-octanoic acid/mL of milk. Exhaled air samples were taken through an original nasal mask. Amounts of (13)C and (12)C in the exhaled air samples were measured by mass spectrometry. Results were expressed as delta over baseline and related to the international standard of Pee Dee Belemnite Limestone. To assess the half-life of elimination (t(1/2)E), we modeled the process of elimination with the incomplete gamma-function, which has a convenient form for the empiric plotting of breath test data. We estimated the parameters of the function, f(x) = A x(b) e(-cx), by using the moment method. The curves were determined by the t(1/2)E of (13)CO(2) and characterized by the shape of the elimination curve. The half-time of gastric emptying (t(1/2)GE) was calculated as t(1/2)E reduced by the mean metabolic half-time of octanoic acid.
Results: Forty-eight (13)C-OABT results from 16 premature newborns were analyzed. The mean and median of t(1/2)GE calculated from all three tests were 50.3 (+/-29.9) and 43.7 min, respectively. The t(1/2)GE did not change significantly (P = 0.6811) with the administered dose of (13)C-primed breast milk in the stomach. The coefficient of variation among the studied infants was 4.0% to 33.6% (mean, 11.5%). In 12 infants, the characteristic type of elimination curve was the same for all three tests.
Conclusions: In the first hours of gastric feeding, neither the age of the neonate nor the amount of administered (13)C-primed breast milk had any effect on t(1/2)GE. The gastric emptying rate and the evacuation curve shape for individual neonates were similar and independent of milk amount.