Intraoperative PEEP Optimization: Effects on Postoperative Pulmonary Complications and Inflammatory Response

Patients undergoing general anesthesia and mechanical ventilation during major abdominal surgery commonly develop pulmonary atelectasis or even hyperdistension of the lungs can occur leading to adverse consequences either intraoperatively or postoperatively. Lung protective ventilation (LPV, PEEP = 6 cmH2O, TV = 6 mL/Kg IBW and regular recruitments) during the intraoperative period can reduce the risk of ventilator induced lung injury (VILI) and prevent the formation of pulmonary atelectasis.

In our investigator-initiated, double-center, single-blinded, prospective, randomized, controlled clinical trial a total number of 40 patients with bladder cancer undergoing open radical cystectomy and urinary diversion (ileal conduit or orthotopic bladder substitute) will be enrolled and randomized into two groups. Standard lung protective mechanical ventilation with the use of 6 cmH2O of PEEP and low tidal volumes (6mL/Kg IBW), a fraction of inspired oxygen (FiO2) of 0.5 and a respiratory rate to maintain an end tidal carbon dioxide (ETCO2) between 35-40 mmHg will be performed in control group, and a strategy of lung protective mechanical ventilation applying an optimal, individual PEEP determined by static pulmonary compliance (Cstat) directed PEEP titration procedure will be performed in study group.

During preoperative assessment, respiratory failure risk index (RFRI) will be recorded and informed consent will be obtained. Regarding to the protocol, a central vein catheter will be placed on the day before surgery, serum procalcitonin (PCT) level will be measured and a chest X-ray examination will be performed.

Before induction of anesthesia, an epidural catheter and an arterial canula for invasive blood pressure monitoring will be inserted. Immediately after induction of anesthesia and orotracheal intubation, all patients will be submitted to an alveolar recruitment maneuver (ARM) using the sustained airway pressure by the CPAP method, applying 30 cmH2O PEEP for 30 seconds. After ARM PEEP will be set to 6 cmH2O in the control group ("standard PEEP") and LPV will be performed. In the study group ("optimal PEEP") PEEP will be set to 14 cmH2O and a Cstat directed decremental PEEP titration procedure will be performed (every 4 minutes PEEP will be decreased by 2 cmH2O, until a final PEEP of 6 cmH2O) to determine the best individual PEEP. During surgery ARM will be repeated and arterial and central vein blood gas samples (ABGs, CVBGs) will be evaluated every 60 minutes. PCT levels will be measured 2, 6, 12, 24, 48 and 72 hours after surgical incision.

After extubation, patients will be addmitted to the Department of Anesthesiology and Intensive Care. ABGs and CVBGs will be collected and evaluated, PaO2/FiO2 and dCO2 will be calculated every 6 hours until 72 hours after surgery. On the first postoperative day chest X-ray will be performed and repeated on the following days if developing of pulmonary complications were suspected. Continuous epidural analgesia will be introduced, and evaluated effective if numeric pain rating scale point would be lower than 3 points.

During postoperative care continuous intraabdominal pressure (IAP) monitoring via a direct intraperitoneal catheter placed before closure of the abdominal wall will be performed to eliminate bias caused by the elevation of intraabdominal pressure.

Patients' clinical progress and secondary endpoints will be monitored by daily SOFA Scores, laboratory and physical examinations.

During follow-up period in-hospital stay, 28-days and in-hospital mortality will also be evaluated.

Inclusion criteria

• Patients with bladder cancer undergoing radical cystectomy and urinary diversion (ileal conduit or orthotopic bladder substitute)

Exclusion criteria

• Age < 18 years
• ASA grade IV
• History of severe chronic obstructive pulmonary disease (COPD, GOLD grade III or IV)
• History of severe or uncontrolled bronchial asthma
• History of severe restrictive pulmonary disease
• Pulmonary metastases
• History of any thoracic surgery
• Need for thoracic drainage before surgery
• Renal replacement therapy prior to surgery
• Congestive heart failure (NYHA grade III or IV)
• Extreme obesity (BMI > 35 Kg/m2)
• Lack of patient's consent