Obesity is a chronic, complex disease defined by the World Health Organization (WHO) as the excessive accumulation of fat in the body that can harm health. Since 1975, the prevalence of obesity has been increasing worldwide, making it a significant public health issue. Body mass index (BMI) is important in diagnosing obesity. BMI is calculated by dividing a person's weight (kg) by the square of their height (m²). BMI: weight (kg) / height² (m²). According to the WHO, a BMI between 30.0-34.9 kg/m² is classified as Class 1 obesity, between 35.0-39.9 kg/m² as Class 2 obesity, between 40-49.9 kg/m² as Class 3 obesity, and ≥50.0 kg/m² as super obesity.

Obesity is closely related to increasing morbidity and mortality worldwide, and in obese patients, the incidence of diseases such as type 2 diabetes, hypertension, cardiovascular disease, dyslipidemia, coronary heart disease, obstructive sleep apnea, asthma, depression, other psychiatric disorders, and gastroesophageal reflux has increased. Treatment options for obesity include lifestyle changes, specific diets, diet-drug combinations, metabolic and various bariatric surgical options. Among these treatment options, metabolic and bariatric surgical procedures are considered the most effective methods for weight loss.

Aspiration of gastric contents is a significant perioperative complication that can cause up to 9% of anesthesia-related deaths. Due to delayed gastric emptying in obese patients, the risk of aspiration is higher compared to non-obese patients. In obese patients, preoperative anesthesia management is more challenging, and the risk of pulmonary aspiration is greater. Since obesity is an independent risk factor for patients with a full stomach, and airway management can be difficult in these patients, it is essential to assess the aspiration risk in the preoperative period.

Anesthesia guidelines recommend that to improve the quality and effectiveness of anesthesia care and reduce the severity of potential complications related to perioperative pulmonary aspiration of gastric contents, adults and children should be allowed to drink clear liquids up to 2 hours before elective surgery, and solid food consumption should be prohibited 6 hours before elective surgery.

Recently, with the integration of ultrasound into anesthesia practice, ultrasound has been applied in various surgical procedures and clinical conditions. The use of ultrasound to evaluate the risk of aspiration in the preoperative period and to determine the residual gastric volume is increasingly being used in clinical practice. The use of gastric ultrasound to assess aspiration risk has also been increasing in pediatric patient groups and pregnant patients, similar to obese patient groups.

In this study, the investigators' aim is to determine the relationship between BMI, fasting duration, and aspiration risk by assessing the gastric residual volume in the preoperative period through gastric ultrasonography in patients with obesity who will undergo bariatric surgery.

Patients will be informed about the study procedure one day before the surgery, and informed consent will be obtained from those who agree to participate. For patients who have given consent, gastric ultrasonography will be performed in the anesthesia preparation room before surgery. The examination will be conducted first in the supine position and then in the right lateral decubitus (RLD) position.

While patients are in the RLD and supine positions, a low-frequency (2-5 MHz) curved ultrasound probe will be used to scan from left to right along the subcostal margin. The left lobe of the liver and the descending abdominal aorta will be used as anterior and posterior landmarks. Gastric content will be evaluated both qualitatively and quantitatively by gastric ultrasonography.

In the RLD position, two maximum perpendicular diameters of the stomach-anteroposterior (AP) and craniocaudal (CC)-will be measured. The antral cross-sectional area (CSA) in the right lateral decubitus position will be calculated using the formula:

CSA = (AP × CC × π) / 4.

Gastric residual volume will then be calculated using the formula by Perlas et al.:

Gastric residual volume (mL) = 27.0 + 14.6 × right lateral CSA - 1.28 × age.

Patients with an empty antrum and gastric residual volume less than 1.5 mL/kg will be considered at low risk for aspiration, whereas those with solid content and/or gastric residual volume greater than 1.5 mL/kg will be considered high risk for aspiration. A flat antrum image with anterior and posterior walls adjacent will be regarded as an empty stomach. A hypoechoic, thin-walled, distended antrum will be interpreted as liquid content, and a distended antrum showing mixed echogenicity on ultrasound will be considered solid content.

Additionally, the antrum will be classified using a three-point grading system:

Grade 0: No fluid visible in both supine and RLD positions.

Grade 1: Clear fluid visible only in the RLD position.

Grade 2: Fluid and solid content visible in both supine and RLD positions.

All measurements will be repeated three times, and the average will be taken. The duration of the ultrasonography procedure will be recorded.

Preoperative laboratory values including fasting blood glucose, HbA1c, renal function tests (urea, creatinine), liver function tests (AST, ALT), serum electrolytes (sodium, potassium, chloride, calcium), hemogram parameters (hemoglobin, hematocrit, platelet, leukocyte), and coagulation parameters (APTT, INR) will be documented.

Demographic data (age, gender, height, weight), BMI, waist circumference, xiphoid circumference, ASA score, comorbidities, previous surgeries, and ongoing medications will also be recorded.

After completing the gastric ultrasonography, patients will be taken to the operating room. Standard monitoring including electrocardiogram (ECG), non-invasive blood pressure, peripheral oxygen saturation (SpO2), and bispectral index (BIS) will be applied. Premedication will be performed with intravenous midazolam 0.02 mg/kg, followed by preoxygenation with 100% oxygen via mask for 3 minutes.

Standard anesthesia induction will be carried out using intravenous propofol 2-2.5 mg/kg, fentanyl 2 mcg/kg, and rocuronium 0.6 mg/kg. Orotracheal intubation will be performed once adequate muscle relaxation is achieved. Mechanical ventilation will be provided in volume control mode with tidal volumes of 6-8 ml/kg and end-tidal carbon dioxide (EtCO2) maintained between 35-40 mmHg.

Anesthesia maintenance will be ensured with sevoflurane 1.5-2% in 2 L/min of 50% oxygen-air mixture and intravenous remifentanil infusion at 0.05-0.5 mcg/kg/min, targeting BIS values between 40-60. Normothermia will be maintained intraoperatively with active forced-air warming devices in all patients.

Perioperative aspiration events will be recorded as "occurred" or "not occurred." Total surgical and anesthesia durations will be documented.

Twenty minutes before the end of surgery, patients will receive postoperative analgesia prophylaxis with intravenous administration of 1 g paracetamol, 1 mg/kg tramadol, and 4 mg ondansetron for nausea and vomiting prophylaxis, according to our standard protocol.

At the end of surgery, anesthetic agents will be discontinued, and the awakening phase will begin. After patients resume spontaneous respiration, neuromuscular blockade will be reversed with intravenous sugammadex 2 mg/kg. Patients with adequate respiratory effort and BIS ≥ 85 will be extubated and transferred to the recovery unit once they are awake, have regained muscle strength, and are hemodynamically stable.

Postoperative nausea will be evaluated at 1, 6, and 24 hours using a 5-point nausea-vomiting severity scale (0 = no nausea, 1 = mild nausea without vomiting, 2 = moderate nausea with vomiting, 3 = vomiting less than twice per hour, 4 = vomiting more than twice per hour) and any complications will be recorded (present/absent).

Inclusion Criteria:

• Patients who will undergo bariatric surgery under general anesthesia in elective conditions
• Patients in ASA II-III groups, with BMI > 35 kg/m², and aged between 18-65 years
• Patients who have provided informed consent

Exclusion Criteria:

• Patients under 18 years of age, over 65 years of age, or in ASA IV-V groups
• Pregnancy
• Patients with upper gastrointestinal (GI) abnormalities such as hiatal hernia and gastric tumors
• Patients with a recent history of upper GI bleeding (within the last 12 months), previous stomach and esophagus surgeries, or abnormal anatomy of the upper gastrointestinal tract
• Patients using medications that affect gastric motility or other related conditions
• Patients with uncontrolled diabetes
• Patients who require emergency surgery
• Patients with advanced cardiac, renal, pulmonary, or hepatic failure
• Patients who refuse to participate and do not provide informed consent

Patients who will undergo bariatric surgery under general anesthesia in elective conditions