European Journal of Cardiovascular Medicine

Pulmonary aspiration of gastric contents is a rare but devastating complication in the perioperative period, associated with significant morbidity and a high mortality rate. The pathophysiological consequence, aspiration pneumonitis, can lead to acute lung injury, respiratory failure, and prolonged hospitalization. This risk is a primary concern for anesthesiologists during the induction of and emergence from general anesthesia, as protective airway reflexes are obtunded.¹

To minimize this risk, standardized preoperative fasting guidelines have been universally adopted. The American Society of Anesthesiologists (ASA) guidelines, for instance, recommend fasting for clear liquids for 2 hours, for breast milk for 4 hours, and for a light meal for 6 hours.^1,2 These protocols are designed to ensure that the stomach is sufficiently empty at the time of anesthesia induction. However, it is critically important to recognize that these guidelines were established primarily for healthy, non-pregnant adult populations without comorbidities known to affect gastrointestinal motility.

A significant challenge arises when managing patients with conditions that predispose them to delayed gastric emptying. Among these, diabetes mellitus and obesity represent two major and increasingly prevalent global health problems. Long-standing diabetes mellitus, particularly when poorly controlled, can lead to diabetic gastroparesis---a form of autonomic neuropathy characterized by delayed gastric emptying in the absence of mechanical obstruction.^3,4 This dysfunction results from damage to the vagus nerve and intrinsic neuronal pathways within the gastric wall, leading to impaired antral contractions and gastropyloric coordination. Consequently, even after adhering to standard fasting durations, diabetic patients may retain significant residual gastric volume, rendering them vulnerable to regurgitation and aspiration.

Similarly, obesity is a recognized independent risk factor for a "full stomach". The pathophysiological mechanisms in obese patients are multifactorial, including increased intra-abdominal pressure, a higher incidence of gastroesophageal reflux disease (GERD), and alterations in gastrointestinal hormone secretion that may influence gastric motility and emptying.^5,6 The sheer volume of food intake and the potential for high-fat content meals can further complicate gastric emptying. Despite these known risks, the optimal preoperative fasting strategy for obese patients remains undefined, and they are often managed under the same protocols as the general population.

The current ASA practice guidelines explicitly acknowledge this knowledge gap, stating that they do not provide specific recommendations for patients at increased risk of delayed gastric emptying or pulmonary aspiration, such as those with diabetes mellitus, morbid obesity, or recent opioid use.² This lack of clear guidance creates a clinical dilemma, forcing anesthesiologists to choose between enforcing potentially unnecessary prolonged fasting---which can lead to patient discomfort, dehydration, and insulin dysregulation in diabetics---or proceeding with an anesthetic plan that may inadvertently carry a higher-than-accepted risk of aspiration.

The advent of bedside gastric ultrasonography has revolutionized the preoperative assessment of gastric content.⁷ This non-invasive, rapid, and reproducible technique allows for real-time qualitative and quantitative evaluation of the gastric antrum. By measuring the cross-sectional area (CSA) of the antrum in specific patient positions, validated mathematical models can reliably estimate gastric fluid volume.^8,9 Furthermore, the sonographic appearance can distinguish between empty, fluid-filled, and solid-containing stomachs, enabling direct risk stratification immediately before induction.

While previous studies have utilized gastric ultrasound to compare diabetic and non-diabetic patients, consistently demonstrating higher residual volumes in the diabetic population^10,11, and a smaller number of studies have investigated gastric volume in obesity⁴, there is a paucity of research that directly compares these three distinct cohorts---diabetics, obese, and healthy controls---within a single study design under standardized fasting conditions. Such a direct comparison is crucial to understand the relative magnitude of risk associated with each condition.

Therefore, this study was designed to bridge this gap in the literature. Our primary aim was to quantitatively compare the preoperative fasting gastric volume among diabetic, non-diabetic, and obese patients undergoing elective surgeries using gastric ultrasonography. We hypothesized that both diabetic and obese patients would exhibit a significantly larger residual gastric volume compared to healthy controls, despite adhering to standard fasting guidelines. The findings of this study will help to refine the preoperative assessment of these high-risk patients and underscore the value of point-of-care gastric ultrasound as an essential tool for personalized, safe anesthetic care.

Study Design and Setting

A prospective, single-blind, observational study was conducted in the Department of Anaesthesiology at MVJ Medical College and Research Hospital, Hoskote, over a period of 12 months. The study was approved by the Institutional Ethics Committee, and written informed consent was obtained from all participants.

Study Population

A total of 150 adult patients (aged 18-60 years) of American Society of Anesthesiologists (ASA) physical status I-IV, scheduled for elective surgeries under general or regional anesthesia, were enrolled. Patients were allocated into three groups of 50 each using simple random sampling:

• Group D (Diabetic): Patients with a history of Type 2 Diabetes Mellitus for at least 6 years.
• Group C (Control): Non-diabetic, non-obese patients (BMI <30 kg/m²).
• Group O (Obese): Non-diabetic patients with a Body Mass Index (BMI) >30 kg/m².

Exclusion Criteria

Patients were excluded if they were taking medications affecting gastric motility (e.g., metoclopramide, opioids), had renal failure, hypothyroidism, connective tissue disorders, a history of gastrointestinal surgery, were parturients, or had a nasogastric tube in situ.

Study Procedure

All patients followed standard institutional fasting guidelines (8 hours for solids, 2 hours for clear fluids). Preoperatively, a detailed history, including diabetic history and drug history, was recorded. A single anesthesiologist, blinded to the patient's group assignment, performed all gastric ultrasound examinations using a curvilinear probe (2-5 MHz).

The patient was initially placed in the supine position. The gastric antrum was identified in a sagittal plane between the left lobe of the liver and the pancreas, posterior to the left lobe. The patient was then turned to the Right Lateral Decubitus (RLD) position. In the RLD position, the anteroposterior (AP) and craniocaudal (CC) diameters of the gastric antrum were measured, and the Cross-Sectional Area (CSA) was calculated using the formula:

CSA (cm²) = (AP × CC × π) / 4

The Gastric Volume (GV) in milliliters was estimated using the validated formula by Perlas et al. [10]:
GV (ml) = 27.0 + (14.6 × RLD CSA) - (1.28 × Age)

The qualitative sonographic appearance of the gastric antrum was graded as per Perlas et al.:

• Grade 0: Empty antrum in both supine and RLD positions.
• Grade 1: Fluid visible only in the RLD position.
• Grade 2: Fluid visible in both supine and RLD positions.

Risk Stratification

Aspiration risk was categorized based on the criteria by Van de Putte and Perlas:

• Low Risk: Empty antrum (Grade 0) or estimated GV < 1.5 mL/kg.
• High Risk: Presence of solid contents or estimated GV > 1.5 mL/kg.

Statistical Analysis

Data were analyzed using SPSS software version 25.0. Continuous variables (age, BMI, fasting duration, AP diameter, CC diameter, CSA, GV) were expressed as mean ± standard deviation and compared using one-way Analysis of Variance (ANOVA) with post-hoc Tukey's test. Categorical variables (sex, ASA grade, aspiration risk) were expressed as numbers and percentages and compared using the Chi-square test. A p-value of less than 0.05 was considered statistically significant.

Table 1: Demographic and Baseline Characteristics

* p<0.05 for comparison with Group D, # p<0.05 for comparison with Group C

The three groups were comparable in terms of baseline demographic parameters. There was no statistically significant difference in the mean age (p=0.08) or sex distribution (p=0.89) among the groups. The preoperative fasting duration was also similar across all groups, with a mean of approximately 10 hours (p=0.45). As defined by the study protocol, the mean Body Mass Index (BMI) was significantly higher in Group O (34.9 ± 3.8 kg/m²) compared to both Group D (27.5 ± 3.1 kg/m²) and Group C (24.8 ± 2.5 kg/m²) (p < 0.001). The distribution of ASA physical status grades was not significantly different among the groups (p=0.12).

Table 2: Ultrasonographic Measurements and Estimated Gastric Volume

* p<0.05 for comparison with Group C, # p<0.05 for comparison with Group D

Analysis of the gastric ultrasound measurements revealed significant differences among the groups. Both the anteroposterior (AP) and craniocaudal (CC) diameters of the gastric antrum, measured in the right lateral decubitus position, were significantly larger in Group D and Group O compared to Group C (p < 0.001 for both diameters). Consequently, the calculated cross-sectional area (CSA) of the antrum followed the same pattern, being largest in Group D (6.9 ± 1.8 cm²), intermediate in Group O (6.1 ± 1.5 cm²), and smallest in Group C (4.7 ± 1.2 cm²) (p < 0.001).

The primary outcome variable, the estimated fasting gastric volume (GV), was significantly different across the groups (p < 0.001). Post-hoc analysis confirmed that Group D had the highest mean gastric volume (45.6 ± 15.2 ml), which was significantly greater than both Group O (38.9 ± 12.8 ml, p < 0.05) and Group C (28.3 ± 9.5 ml, p < 0.001). Furthermore, the gastric volume in Group O was also significantly higher than in Group C (p < 0.001). When gastric volume was normalized to body weight (GV/kg), the same statistical hierarchy was maintained (Group D > Group O > Group C, p < 0.001).

Table 3: Qualitative Gastric Antrum Grading and Aspiration Risk Stratification

*p<0.05 for comparison with Group C, # p<0.05 for comparison with Group D

The qualitative assessment of the gastric antrum showed a significantly different distribution of Perlas grades among the groups (p < 0.01). A notably higher proportion of patients in Group C (64%) had a completely empty antrum (Grade 0) compared to Group D (30%) and Group O (40%). Conversely, the presence of fluid in both supine and RLD positions (Grade 2) was observed only in Group D (18%) and Group O (10%), with no Grade 2 antra in the control group.

This translated directly into the stratification of aspiration risk. A significantly higher proportion of patients in both Group D (18%, 9/50) and Group O (10%, 5/50) were classified as "high risk" for pulmonary aspiration based on a gastric volume > 1.5 ml/kg, whereas none of the patients in Group C (0%) fell into this high-risk category (p < 0.01). The difference in the high-risk proportion between Group D and Group O was not statistically significant. It is important to note that no solid contents were visualized in any patient across all three groups.

This prospective, observational study demonstrates that patients with diabetes and obesity present for elective surgery with a significantly higher residual gastric volume after a standard preoperative fast compared to healthy, non-diabetic controls. This key finding, objectively quantified by bedside ultrasonography, underscores a tangible physiological difference that has direct implications for perioperative risk stratification. Our results strongly suggest that the conventional practice of relying solely on fasting duration is insufficient to guarantee a low-risk stomach in these patient populations.

The most pronounced difference was observed in patients with long-standing diabetes. The mean gastric volume in Group D was over 60% higher than in the control group, and 18% of these diabetic patients were classified as high-risk for aspiration. This is a clinically significant proportion that would likely be missed by history-taking alone. This finding is consistent with the pathophysiological understanding of diabetic gastroparesis, where autonomic neuropathy disrupts gastric motility and pyloric function.1,3 Our results align closely with those of Garg H et al. (2020)8, who, in their comparative study, also reported a significantly larger antral cross-sectional area and calculated gastric volume in diabetic patients versus non-diabetics. They concluded that diabetic patients have a "fuller stomach" despite adequate fasting, a conclusion our data robustly supports. Furthermore, our study extends the findings of Rajeswari L et al. (2022)9, who similarly used ultrasound to find a higher mean gastric residual volume in diabetics and advocated for point-of-care ultrasound as a screening tool. Our study strengthens this recommendation by providing a direct, quantitative comparison within a three-group design, clearly delineating the risk in diabetics from both healthy and obese individuals.

Interestingly, our obese cohort exhibited an intermediate phenotype. While their mean gastric volume was significantly lower than that of the diabetic group, it was still substantially higher than that of the healthy controls. This indicates that obesity itself is an independent risk factor for increased residual gastric volume, albeit potentially through mechanisms different from diabetic neuropathy. Potential explanations include chronic gastric compression from increased intra-abdominal pressure, a higher prevalence of gastroesophageal reflux disease, and dietary habits.5,6 Our findings partially contrast with those of Khalil et al. (2021)4, who reported a larger antral CSA in obese patients but concluded that both obese and normal-weight participants had a low predicted gastric residual volume. This discrepancy may be attributed to differences in the patient population, the specific formula used for volume calculation, or sample size. However, the critical finding in our study is that 10% of our obese patients crossed the threshold into the high-risk category, a non-trivial percentage that justifies a more cautious preoperative evaluation.

A pivotal observation across all three groups was the lack of a significant correlation between fasting duration and gastric volume. All patients fasted for a comparable and protocol-adherent duration (mean ~10 hours), yet the residual volumes varied dramatically based on their comorbidity profile. This finding is a powerful validation of the work by Sharma S et al. (2018)12, who conducted a clinical audit and found that 28% of their patients had a large residual gastric volume, with the presence of risk factors being a stronger predictor than the length of fasting. Our data confirm that while standard fasting guidelines are effective for the general population, they do not account for the altered gastric physiology in high-risk groups like diabetics and the obese. The stomach in these patients does not empty at the same rate, making temporal fasting guidelines an unreliable safeguard.

In conclusion, this study provides compelling ultrasonographic evidence that patients with diabetes and obesity are at a significantly higher risk of having elevated residual gastric volume after preoperative fasting. This elevated volume places a substantial subset of these patients in a higher aspiration risk category. Fasting duration alone is a poor predictor of gastric content in these populations. Therefore, the routine application of qualitative and quantitative gastric ultrasonography should be integrated into the preoperative workflow for high-risk patients. This practice enables an objective, individualized risk assessment, allowing anesthesiologists to rationally tailor their airway management strategy—opting for rapid-sequence induction when indicated or proceeding with greater confidence when the stomach is confirmed to be empty—thereby enhancing patient safety through precision anesthesia.