Ultrasound for Prediction of Empty Stomach in Infants

Protocol: This study was performed in Pediatric Gastrointestinal (GI) Endoscopy Unit after receiving Institutional Ethics Board approval. Following induction of anaesthesia, antral sonography was performed in supine and right lateral decubitus (RLD) positions in 46 fasted infants prior to upper GI endoscopic evaluation. Antral CSA measurements in both positions and the qualitative evaluation of the antrum (according to the 3-point grading system) were recorded. Grade 0: antrum appears empty in both positions. Grade 1: antrum appears empty in the supine position but a small volume of gastric clear fluid is visible in the RLD. Grade 2: antral clear fluid visualized in both the supine and RLD position. The calculation of the antral CSA was performed by measuring the longitudinal diameter (D1) and the antero-posterior diameter (D2) of the antrum at rest, between peristaltic contractions, from serosa to serosa. Cross-sectional area was calculated using the standard formula for surface area of an ellipse CSA= π x D1 x D2 / 4. Gastric contents were endoscopically suctioned and measured by a graduated specimen trap with 1 ml increments.

Sample size A sample of 23 from the positive group and 23 from the negative group achieve 80% power to detect a difference of 0,2300 between the area under the receiver operating characteristic (ROC) curve (AUC) under the null hypothesis of ,5000 and an AUC under the alternative hypothesis of 0,7300 using a two-sided z-test at a significance level of 0,05000. The data are continuous responses. The AUC is computed between false positive rates of 0,000 and 1,000. The ratio of the standard deviation of the responses in the negative group to the standard deviation of the responses in the positive group is 1,000.

Statistical analysis:

All statistical analysis was performed using IBM SPSS for Windows Version 23.0 software. Descriptive statistics for continuous variables were shown as mean ± standard deviation (SD) or median [inter-quartile range (IQR); 25-75th percentile]. Categorical variables were shown as the number of patients and percentage (%). Whether the distributions of continuous variables were normal or not was determined by the Shapiro Wilks test. Correlations between continuous variables were given by Spearman Correlation Coefficient. Discriminative ability of the CSA was determined by ROC curve analysis. Optimal cut-off value was given by Youden index. Sensitivity, specificity, positive and negative predictive value were calculated at this point. A p value less than 0.05 was considered statistically significant.

Stepwise linear regression analysis was applied to estimate CSA. The variables those p values <0.20 in the univariate analysis were included in multiple regression model. The independent variables were determined as age, BMI and CSA-RLD. The adequacy of the established regression models was demonstrated by R2.