Evaluating Respiratory Effects of Driving Pressure Guided Mechanical Ventilation Using Electrical Impedance Tomography in Patients Undergoing Robot-Assisted Laparoscopic Radical Prostatectomy

General anesthesia increases the risk of respiratory complications and impairs arterial oxygenation by causing atelectasis in the dorsal regions of the lungs. Postoperative pulmonary complications (PPC) represent events such as atelectasis, pulmonary edema, pneumonia, pleuritis, reintubation, and the need for oxygen support after surgery, and are associated with increased morbidity, mortality, intensive care, and hospital stay durations, as well as higher healthcare costs. The effective strategy to reduce the incidence of PPC in patients under general anesthesia is still not clear.

Robot-assisted surgeries are increasingly preferred for prostatectomy, a curative treatment for prostate cancer, due to advantages such as less blood loss, less scar tissue formation, and shorter hospital stays compared to other surgical methods. During robotic surgery, many factors such as laparoscopy, pneumoperitoneum, and extreme Trendelenburg position can negatively affect lung function. Studies have shown that high driving pressure values, resulting from the set tidal volume target and PEEP values during mechanical ventilation, increase postoperative pulmonary complications.

Developing mechanical ventilation strategies based on personalized PEEP values that provide the lowest driving pressure after recruitment maneuvers to include closed alveoli in respiration and monitoring the effects of this method on the lungs during the perioperative period using electrical impedance tomography (EIT) is a highly useful tool. EIT, a non-invasive, radiation-free bedside monitoring system that detects real-time regional ventilation changes, can be used to guide individualized protective ventilation strategies to reduce perioperative respiratory system complications. Examining ROI values measured by EIT shows the effect of ventilation strategies on the distribution of tidal volume in the lungs. ROIs calculated by selecting layers, with ROI 1 and ROI 2 reflecting the ventral parts and ROI 3 and ROI 4 reflecting the dorsal parts, can be used to demonstrate the effect of the chosen ventilation strategy on lung gas distribution through intergroup comparison.

The age, gender, height, weight, body mass index, diagnosis, ASA score, preoperative hemoglobin level, additional systemic diseases, smoking history, prostate-specific antigen level, Gleason score, and prostate volume of the patients will be recorded. All patients will be monitored with electrocardiogram (ECG), peripheral oxygen saturation (SpO2), invasive arterial pressure (systolic arterial pressure, diastolic arterial pressure, and mean arterial pressure), and electrical impedance tomography. Patients will be prospectively randomized into two groups; group assignments will be determined using a closed-envelope technique.

All patients will be preoxygenated with 80% FiO2, followed by induction of anesthesia with 2 mcg/kg fentanyl, 2 mg/kg propofol, and 0.6 mg/kg rocuronium. After orotracheal intubation, patients will be placed on mechanical ventilation in volume control-autoflow mode with 8 ml/kg tidal volume, 2 L/min fresh gas flow, 0.4 inspired fractional oxygen (FiO2), an inspiratory: expiratory ratio of 1:2, and a respiratory rate to achieve normocapnia (partial carbon dioxide pressure PaCO2: 35-45 mmHg). Recruitment maneuvers will be applied to all patients.

During the recruitment maneuver: with an inspiratory: expiratory ratio of 1:1, a respiratory rate of 12 breaths/min, ventilation with a tidal volume of 8 ml/kg will be applied for 1 minute at a PEEP level of 5 cmH2O. This will be followed by ventilation with a tidal volume of 10 ml/kg for 1 minute at 10 cmH2O PEEP, and finally, ventilation with a tidal volume of 12 ml/kg for 1 minute at 15 cmH2O PEEP.The mechanical ventilation strategies for the patients will be planned according to their group.

For all patients, systolic arterial pressure, diastolic arterial pressure, mean arterial pressure, heart rate, and SpO2 values will be recorded before induction, after intubation, at 5-minute intervals for up to 60 minutes after pneumoperitoneum and Trendelenburg position, at 60 minutes after Trendelenburg position , at 75 minutes after Trendelenburg position , at 90 minutes after Trendelenburg position, at 120 minutes after Trendelenburg position, at 180 minutes after Trendelenburg position, at 240 minutes after Trendelenburg position, before extubation, 5 minutes after extubation , at 60 minutes postoperatively , at 24 hours postoperatively , and at 48 hours postoperatively . Additionally, while the patient is on mechanical ventilation, peak pressure, plateau pressure, PEEP, mean airway pressure (MPaw), compliance, and end-tidal carbon dioxide values will also be recorded.

Intermittent arterial blood gas analysis with invasive arterial monitoring is a routine practice in our daily practice. Arterial blood gas analysis will be performed preoperatively, immediately after intubation, at 15, 60, and 120 minutes after pneumoperitoneum and Trendelenburg position, immediately before extubation, and 5 minutes after extubation, with pH, partial oxygen pressure (pO2), partial carbon dioxide pressure (pCO2), oxygenation index (pO2/FiO2), bicarbonate, lactate, and hemoglobin values recorded.

Anesthesia duration, perioperative fluid volume, perioperative blood loss and urine output, operation duration, pneumoperitoneum duration, mechanical ventilation duration, and vasoactive agent use duration will be recorded.

In all patients, ROI values measured by electrical impedance tomography, which we use routinely in our daily practice, will be recorded before intubation, immediately after intubation, at 15, 60, and 120 minutes after pneumoperitoneum and Trendelenburg position, immediately before extubation in the supine position, and 5 minutes after extubation.

Postoperative pulmonary complications in patients will be monitored using SpO2, fever, cough, and sputum history, as well as prolonged intubation if present, and the duration of oxygen support and the development of additional pathology will be recorded.

Inclusion criteria

• ASA score of I-II-III according to the American Society of Anesthesiologists (ASA) physical status classification system
• Surgery duration is expected to be longer than 2 hours

Exclusion criteria

• Patients who underwent surgery requiring mechanical ventilation for more than 1 hour within 2 weeks before the operation
• Patients with a body mass index over 35
• Patients with large bullae or pneumothorax, those currently receiving oxygen support, those with severe respiratory disease
• Patients with severe heart failure classified as NYHA class III-IV by the New York Heart Association (NYHA), those with a pacemaker or cardiac defibrillator implant
• Patients with progressive neuromuscular disease
• Patients who refused to participate in the study were excluded.