Ultrasonographic evaluation of gastric content and volume after oral ingestion of water or jelly in volunteers: a randomised controlled non‐inferiority clinical trial

The American Society of Anesthesiologists advises clear fluid intake for elective patients up to 2 h before surgery. Jelly, although a solid food, is primarily composed of water, and the precise fasting time for this substance is not clearly defined [1, 2]. The aim of this study was to investigate the effect of water and jelly ingestion on cross-sectional area of the gastric antrum, when assessed by ultrasound. Approval was gained from the local institutional review board. After written, informed consent, healthy adult participants were evaluated on two days after a fast of at least 8 h. On day 1, participants were allocated randomly using online randomisation software to either group Water (ingestion of 102 ml of bottled water) or group Jelly (ingestion of 102 ml of jelly: 78 kcal; 18 g carbohydrate; 1.6 g protein). On day 2, participants received the other intervention. An ultrasound assessment was performed before ingestion (baseline; T0) and then 120 min later (T120). All ultrasound examinations were performed in the right lateral decubitus position by the same investigator, who was blinded to group allocation. Qualitative and quantitative measurements of the gastric antrum were assessed. For quantitative assessment, anteroposterior and craniocaudal diameters were measured. The cross-sectional area of the gastric antrum was calculated using the formula for the area of an ellipse and the gastric volume was determined using the formula by Perlas et al. [3]. We also assessed the proportion of participants with gastric volume > 1.5 ml.kg-1 and the participants' sensations of thirst and hunger at T120 (using a visual analogue scale of 0–10). We hypothesised that jelly intake was associated with a gastric antral cross-sectional area comparable with water at T120. A non-inferiority δ of 2.8 has been described [4] but, as this can be overestimated, we assumed a non-inferiority margin of 1.5. For qualitative assessment, the stomach was classified as ‘empty’; ‘fluid’; or ‘solid’ [5]. Statistical analysis was performed using SPSS 26.0 (SPSS, Inc, Chicago, IL, USA) using t-paired test, Wilcoxon test or Fisher's exact test as appropriate. The significance level was assumed as two-tailed, with an α of 0.05, except for the non-inferiority analysis, where one-tailed p value, with an α of 0.025 was considered. We studied 25 participants (16 female; mean (SD) age 37 (7.8) y; and mean BMI (SD) 23.6 (3.1) kg.m-2). Fasting times were similar between groups (Table 1). At T0, there was no statistically significant differences in the antral cross-sectional area, gastric volume or the proportion of participants with gastric volume > 1.5 ml.kg-1 (Table 1). The difference in median (95%CI) antral cross-sectional area at T120 between the groups was 0.5 (-0.4–1.4) cm-2. The upper confidence limit of the difference in median was below the non-inferiority margin of 1.5. All other variables measured at T120 (gastric volume; proportion of participants with gastric volume > 1.5 ml.kg-1; qualitative assessment; thirst and hunger) were similar between groups. We found non-inferiority for the primary outcome, meaning that jelly ingestion was not linked with higher antral cross-sectional area measurements, and that jelly behaves similarly to clear fluids in terms of gastric effect. Furthermore, we found no statistically significant differences in any of the other studied outcomes. According to previous studies, the ingestion of carbohydrate-rich drinks, up to 2 h before anaesthesia is safe [5]. However, the presence of protein content can delay gastric emptying [6], which does not seem to be the case with jelly. In the absence of solid content, a gastric volume < 1.5 ml.kg-1 appears to be safe and common in fasting patients, mostly representing basal gastric secretions [7]. Our study has some limitations. We studied a population of healthy adults, and the results may therefore not be generalisable to all surgical patients. None of our participants experienced peri-operative anxiety that may influence gastric emptying. Therefore, the true risk of pulmonary aspiration can be difficult to estimate. It will be important to conduct a similar study in a more heterogeneous population in the peri-operative context. This study was registered at clinicaltrials.gov (NCT05737641). Data and statistical code are available upon request from the corresponding author. No external funding or competing interests declared.