Effects of Mechanical Ventilation Guided by Transpulmonary Pressure on Gas Exchange During Robotic Surgery

INTRODUCTION Laparoscopy and robotic techniques are widespread procedures for pelvic gynecologic, urologic and abdominal surgery often performed in Trendelenburg position. Furthermore, in order to ameliorate surgical procedures, pneumoperitoneum is applied by inflating carbon dioxide. However, the rise in abdominal pressure following pneumoperitoneum and the head down body position have been shown to impair the respiratory function during the procedure, mainly inducing atelectasis formation in the declive lung regions. Consequently, functional residual capacity decreases and the risk of perioperative complications, such as hypoxaemia, rises up, particularly if patients are obese. Formation of atelectasis may worsen stress and strain of the alveolar structure. Stress, strain and atelectrauma give rise to ventilator-induced lung injury.

Although the role of ventilator-induced lung injury during general anesthesia is unclear, several investigations have been conducted with the purpose of improving arterial oxygenation and respiratory mechanics during laparoscopy. A ventilator strategy providing positive end-expiratory pressure (PEEP) has been shown to reduce the diaphragm cranial shift, increasing functional residual capacity and decreasing respiratory system elastance, principally in the obese subjects. Furthermore, the application of recruiting maneuver followed by the subsequent application of PEEP improved oxygenation during laparoscopy. Cinnella et al. demonstrated that an open lung strategy, i.e. a ventilation supported by recruiting maneuvers followed by the subsequent application of PEEP applied after pneumoperitoneum induction, increased transpulmonary pressure and led to alveolar recruitment and improvement of elastance of chest wall and gas exchange. These results are in accordance with finding by Talmor et al, evaluating the effect of a mechanical ventilation guided by esophageal pressure in acute lung injury patients.

However a comparison between an esophageal pressure piloted mechanical ventilation and a conventional low tidal ventilator strategy with adjunct of PEEP and recruitment maneuvers according to clinical judgment has never been investigated in patients undergoing robotic gynecologic, abdominal or urologic surgery.

Aim The investigators aim to compare the conventional ventilation strategy (i.e., with application of PEEP and recruitment manoeuvre) with a ventilation driven by transpulmonary pressure assessed through an esophageal catheter, in patients undergoing to robotic surgery, with respect to oxygenation, expressed in terms of arterial oxygen tension - inspired oxygen fraction ratio (PaO2/FiO2) (primary endpoint), intraoperative respiratory mechanics indexes, number of lung recruitment maneuvers, rate and type of perioperative complications until hospital discharge (additional endpoint).

METHODS Patients For this protocol, after informed consent has been obtained, 26 patients will be enrolled in the pilot randomized interventional study, eligible for robotic gynecological, urological and abdominal surgery at Maggiore Hospital Novara Italy.