We screened 419 patients in the age group of 18–80 years of ASA physical status I and II scheduled to undergo elective surgery under general or regional anaesthesia. 411 were included for assessing the GRV using gastric ultrasound as they fulfilled the inclusion criterion. Two patients were excluded from the analysis due to incomplete data (Fig. 4).

The mean age of our study population was 42.2 years. There were more males (55%) than females in our study population. Although we did not recruit patients with a BMI of more than 35%, more than half the population had a body mass index (BMI) of more than 25 and was classified as overweight (BMI > 25 and < 30) or obese (BMI 30–35). 8.1% of the population had a BMI of under 18 and was classified as underweight. 43.7% of the patients suffered from comorbidities such as hypertension, diabetes mellitus type 2, hypothyroidism and obesity. The mean fasting time of patients for solid food was 11 h, and it was 2 h for clear fluids. All patients received premedication for aspiration prophylaxis the night before surgery and the morning of surgery. Most patients (91.7%) received proton pump inhibitors (PPI), and 8.3% received histamine blockers (Table 1).

Preoperative gastric ultrasound was performed in both supine and RLD positions in the sagittal plane. A qualitative assessment was performed, including the content type and antral shape. This was followed by a quantitative evaluation which involved antral measurements in both anteroposterior and craniocaudal diameters, which were used to calculate antral CSA, and then the estimated GRV was derived.

Preoperative gastric ultrasound qualitative assessment involved identifying different antral shapes and describing the content based on echogenicity. Flat and bull’s eye appearance of antrum was considered empty and distended appearance was viewed as the presence of contents which were further described as solid (hyperechoic), liquid (hypoechoic) or mixed (hyperechoic and hypoechoic). 97 and 118 patients were found to have distended stomachs in the supine and right lateral position, respectively (Table 2).

The antral measurements and the calculated gastric residual volume are given in Table 3.

On calculating the aspiration risk, we found 336 patients had a safe gastric residual volume, and 60 patients had a gastric volume of less than 1.5 ml/kg, which implies a low risk for aspiration. However, 13 patients had a GRV of more than 1.5 ml/kg, making them more prone to aspiration.

We divided our study population into those whose fasting hours were less than 10 h and those in whom it was more. On comparing their gastric volumes, the difference was not found to be statistically significant. Eight patients with a fasting duration of more than 10 h and five patients who fasted between 6 and 10 h had a GRV of more than 1.5 ml/h, thus potentially making them high-risk candidates for pulmonary aspiration.

We found that patients premedicated with histamine blockers had a statistically significant higher antral CSA (p-value-0.022*) and GRV (p-value − 0.018*) in the RLD position (antral CSA − 5.49 ± 2.14; GRV − 51.84 ± 35.49) as compared to those who had taken PPIs (antral CSA − 4.75 ± 2.02; GRV − 41.25 ± 28.30).

Patients were divided into four groups according to their BMI. They included, underweight (N-33; BMI < 18.5 kg/m2), normal weight (N-168; BMI 18.5–25 kg/m2), overweight (N-153; BMI 25–30 kg/m2) and obese (N-55; BMI 30–35 kg/m2). In overweight patients, the mean antral CSA in supine and RLD positions were 4.50 ± 1.57 and 4.94 ± 1.96, respectively. In obese patients, the mean antral CSA in supine and RLD positions were 6.04 ± 2.22 and 6.59 ± 2.30, respectively. As BMI increased, there was a statistically (p-value < 0.001**) significant increase in mean antral CSA in both supine and RLD positions. The mean GRV in supine and RLD positions in overweight patients were also found to be 35.11 ± 23.60 and 42.22 ± 31.39, respectively. In obese patients, the mean GRV in supine and RLD positions was 56.51 ± 30.06 and 65.07 ± 31.03, respectively. As BMI increased, there was a statistically (p-value < 0.001**) significant increase in mean GRV in both supine and RLD positions (Fig. 5).

Correlation of GRV with BMI

After a qualitative and quantitative assessment of the stomach was made using ultrasound, patients were classified according to the antral grading system using estimated GRV. Different patient factors, including age, sex, BMI, ASA physical status, fasting duration for solids, fasting duration for liquids and type 2 diabetes mellitus, were subjected to univariate analysis to identify any influence of these factors on antral grade. It was observed that there were no statistically significant association between age (p-value − 0.74), sex (p-value − 0.99), ASA physical status (p-value − 0.13), fasting hours for solids (p-value − 0.18) and liquids (p-value − 0.15) with antral grade. However, there was a statistically significant association found between BMI (p-value − 0.026*) and type 2 diabetes (p-value 0.045*) with antral grade. Among 409 patients, 32 were type 2 diabetic, and 3/32 (9.37%) were found to have GRV > 1.5 ml/kg. Five overweight and one obese patient also had a GRV > 1.5 ml/kg (Table 4).