Correlation of Preoperative Gastric Residual Volume With Body Mass Index and Aspiration Risk in Laparoscopic 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).