Ultrasound examination of the antrum to predict gastric content volume in the third trimester of pregnancy as assessed by MRI

BACKGROUND Ultrasound examination of the gastric antrum allows reliable pre-operative assessment of gastric contents and volume in adult patients. However, during pregnancy, the change in the anatomical position of the stomach due to the gravid uterus leads to a change in the measured value of the antral area. Therefore, current mathematical models predicting gastric content volume (GCV) in the adult may not apply in term pregnant women. OBJECTIVE To propose a mathematical model which is predictive of GCV in pregnant women and to assess the performance of an ultrasound qualitative grading scale (0 to 2) for the diagnosis of clear fluid volumes more than 0.8 and 1.5 ml kg−1. DESIGN Prospective cohort study. SETTING Hospices Civils de Lyon, Hôpital Femme Mère Enfant, Lyon and Assistance Publique – Hôpitaux de Marseille, Hôpital Nord, Marseille, France. PATIENTS Pregnant women in the third trimester of pregnancy. MAIN OUTCOME MEASURES Comparison of the GCV as measured by MRI and the ultrasound measured antral cross-sectional area, and an assessment of gastric contents according to a 0 to 2 qualitative grading scale. RESULTS Data from 34 women were analysed. A linear model predictive of GCV was constructed with a 95% agreement band of ±95 ml, with a mean polar angle of −8.7°. Performance of the qualitative grading scale to detect fluid volumes >0.8 and >1.5 ml kg−1 was improved when used in a composite scale including a 505 mm2 antral area cut-off value in the semirecumbent supine position. CONCLUSION We report a new mathematical model predictive of GCV in women in the third trimester of pregnancy. Furthermore, the combination of the qualitative and the quantitative ultrasound examination of the gastric antrum might be useful to assess gastric fluid volume in pregnant women. TRIAL REGISTRATION ANSM Register N°2015-A00800-49