Lung-protective Mechanical Ventilation for Patients Undergoing Abdominal Laparoscopic Surgeries: A Randomized Controlled Trial

Study population. We performed a randomized, double-blind controlled trial at Vietnam National Cancer Hospital from January 2020 to July 2020. The trial protocol was approved by the medical ethics committee of Vietnam Military Medical University and Vietnam National Cancer Hospital, simultaneously written informed consent was obtained from all patients before inclusion.

Randomization and blinding technique. Participants were randomly assigned to receive either lung-protective ventilation (LPV group) or conventional ventilation (CV group) at a ratio of 1:1. The randomization was performed using the R program with the "runif", "as.integer", "int" and "replace" functions. As a result, a list of random numbers was created in each group. The patients were numbered according to their orders of hospital registration and then were allocated into the group of their numbers. The intervention protocol was stored in sealed, opaque numbered envelopes. An anesthesiologist who did not involve in the study set the ventilator in accordance with the protocol in the envelopes. Another anesthetist who was in charge of the patient collected data during surgery. The surgeons taking part in the procedures and patients were not informed of the ventilator setting. Physicians in post-anesthesia care unit who were not responsible for intraoperative care carried out the postoperative evaluation. The analysis of the postoperative chest X-ray was completed by a radiologist who was not involved in the study.

Standard procedure. All patients fasted for 12 hours before the procedure but still consumed clear water until 2 hours prior to surgery in order to avoid preoperative dehydration. Participants were premedicated with intravenous midazolam 1-2 mg 30 minutes before the surgery. In the operating room, a radical arterial cannula was inserted to monitor invasive blood pressure, collect blood gas sample, and measure the pulse pressure variation (PPV) index to guide intraoperative fluid therapy. The ASA standards for monitoring such as pulse oximeter, capnography, electrocardiography, thermometer were applied prior to the insertion of an epidural catheter at level T7-T12 for postoperative analgesia.

All patients received intravenous fentanyl 2 µg/kg, lidocaine 40 mg, propofol 2 mg/kg, and rocuronium 1 mg/kg for the induction. Intubation was performed 90 seconds after the administration of muscle relaxant and then 8 mg dexamethasone was injected. Anesthesia was maintained using sevoflurane of which the concentration was justified to achieve the end-tidal concentration within the range of 1,4-1,8 in oxygen and the PRST score less than 3. If the PRST score was greater than 3, then an additional bolus dose of 20-30 mg propofol and 25-50 µg fentanyl was injected along with increasing sevoflurane concentration. On the contrary, if signs of deep anesthesia were presented (PRST score=0, blood pressure decreased by more than 20% of the baseline values, bradycardia), then the sevoflurane concentration was cut down and 100 ml of crystalloid solution was rapidly infused within 2 minutes. A bolus dose of 100-200 µg phenylephrine was added if the blood pressure was still less than 20% of the baseline value in spite of these above-mentioned steps. Rocuronium was continuously infused at the rate of 10 µg/kg/min. The solution of bupivacaine 0,1% combined with fentanyl 2 µg/ml was infused via the epidural catheter at the rate of 5 ml/hour after a loading dose of 5 ml prior to skin incision. Normothermia was maintained during surgery. The pneumoperitoneum was implemented by CO2 insufflation at a pressure of 12 mmHg with room temperature in all patients. The intraoperative fluid was managed based on the goal-directed fluid therapy with a crystalloid solution. In brief, no additional fluids were provided if PPV was lower than 10%, otherwise, additional boluses of 250 ml ringer lactate solution were given over 10-15 minutes. After each bolus dose, PPV was re-assessed and further bolus was administered until reaching a PPV of lower than 10 %.

Intravenous 8 mg ondansetron was injected 30 minutes before the end of surgery to prevent postoperative nausea and vomiting. Rocuronium infusion was stopped 30 minutes before abdominal closure. The neuromuscular blockade was reversed in the postoperative care unit using intravenous neostigmine 40-60 µg/kg combined with atropine 0,5 mg. Patients were extubated when they met the extubation criteria (spontaneous tidal volume > 6 ml/kg and respiratory rate = 12-20 breath/minute, SpO2>95%, normocarbia, body temperature > 350C, positive gag reflexes and ability to follow a verbal command, hemodynamic stability without vasopressor support and ability to lift their heads and hold for 30 seconds [23]). Postoperative epidural analgesia for 48 hours was executed using bupivacaine 0,1% combined with fentanyl 2 µg/ml at a speed of infusion 5-10 ml/hour to maintain a visual analogue scale (VAS) score < 3. If the score was greater than 3, then a bolus dose 5 ml of the anesthetic solution was provided along with an increase in the speed of infusion. After extubation, patients were oxygenated via nasal cannula 3-5 ml/minute (1 ml/minute raises the FiO2 by 3%) to keep the SpO2>95%.