Effect of Intraoperative Position Change on Hemodynamics and Electrocardiography

Morbidly obese patients who will undergo laparoscopic sleeve gastrectomy will be included in the study.

Patients will be taken to the operating room without premedication after a minimum of 8 hours of fasting. Venous access will be established with a 22 G angiocatheter on the operating table. Routine heart rate, arterial blood pressure, peripheral oxygen saturation (SpO₂), body temperature, bispectral index (BIS) (Bispectral Drager Vista 120 system, Covidien, USA) monitoring will be performed. BIS will be kept between 40 - 60. In addition, 12-lead ECG (Cardioline®) will be used for electrocardiogram (ECG) measurements.

Mechanical ventilation will be provided with a tidal volume of 8 mL/kg (IBW) and a positive end expiratory pressure (PEEP) of 8 cmH₂O. The respiratory rate will be adjusted to maintain end-tidal carbon dioxide (EtCO2) at 35 to 45 mmHg.

Targeted Fluid Management (GDFM) will be provided by continuous Pleth Variability Index (PVI) monitoring by placing a Pulse CO-Oximeter sensor system (Masimo rainbow set® Masimo Corporation, Irvine, CA, USA) on the patients' 4th finger. Hemodynamic targets are both PVI and mean arterial pressure. Fluid loading prescription is based on a PVI value greater than 13%, and vasopressor use is based on a mean arterial pressure < 65 mmHg. If necessary, additional fluids and norepinephrine will be given to maintain mean arterial pressure > 65 mmHg.

A 12-lead ECG will be taken at five intraoperative position measurement points (1. Supine-monitored; 2. After induction; 3. Under general anesthesia-Supine-abdominal inflated; 4. Abdominal inflated-(30% upright) Reverse Trendelenburg; 5. Abdominal deflated-(30% upright) Reverse Trendelenburg). Hemodynamic monitoring [systolic blood pressure (SBP), diastolic blood pressure (DAB), mean arterial pressure (MAP), heart rate (HR)] will be recorded at 5 simultaneous measurement points. All hemodynamic measurements and ECG recordings will be made 3 minutes after the position change to ensure standardization, allow the response to settle after the position change, and prevent the possibility of exaggerated or false data.

All patients will have their surgeries performed by the same surgical team and intra-abdominal pressure will be kept below 15 mmHg.

Demographic data (age, gender, height, weight, BMI), American Society of Anesthesiologists (ASA) physical status classification, preoperative assessment information (comorbidities, medications used), duration of surgery and anesthesia, amount of fluid administered, and amount of norepinephrine to be used when needed will be recorded.

Power analysis was calculated as follows:

Repeated measures, within factors Options: Pillai V, O'Brien-Shieh Algorithm Analysis: A priori: Compute required sample size Input: Effect size f = 0.25 α = 0.05 Power (1-β ) = 0.95 Number of groups = 1 Number of measurements = 5 Corr among rep measures = 0 Output: Noncentrality parameter λ = 20.3125000 Critical F = 2.5226149 Numerator df = 4.0000000 Denominator df = 61.0000000 Total sample size = 65 Actual power = 0.9523977 Pillai V = 0.2380952 Considering that there may be data loss in ECG measurements and evaluations, the number of cases was determined as 80 patients.

Intraoperative hemodynamic and ECG (Heart-electrophysiological balance index (iCEB = QT/QRS ratio) changes in 5 positions will be evaluated.

Inclusion criteria

• Adult patient planned for elective primary laparoscopic sleeve gastrectomy surgery
• Body Mass Index (BMI) ≥ 40 kg/ / m²
• Age ≥ 18
• ASA physical health class II-III.

Exclusion criteria

• Patient refusal to participate in the study
• Those who underwent revision laparoscopic sleeve gastrectomy
• Emergency laparoscopic sleeve gastrectomy surgery (stump leakage, etc.)
• Secondary surgery in addition to elective laparoscopic sleeve gastrectomy
• Patients with previous recurrent abdominal surgery
• Patients with electrolyte imbalance
• Direct laryngoscopy in ramp position
• Multiple intubation attempts due to difficult intubation
• Preoperative arrhythmia and heart failure (ejection fraction < 30%)
• Renal and liver failure
• Patients who require > 8 ml/kg for tidal volume