The effects of protective lung ventilation on regional cerebral oxygen saturation in intracranial tumor operative during dura opening：study protocol for a randomized controlled trial

Objective:To investigate the effects of protective lung ventilation on regional cerebral oxygen saturation during dura opening, that is from after dura opening (T1a) to before dura closing (T2b), in patients undergoing intracranial tumor surgery. Methods: This is a randomized, controlled trial which will be carried out at the second affiliated hospital of Soochow University. Fifty-four patients undergoing intracranial tumor surgery will be randomly allocated to the control group and the protective lung ventilation group. In the control group, tidal volume (VT) will be set at 8 ml/kg of ideal body weight, but positive end-expiratory pressure (PEEP) and recruitment maneuvers will not be used. In the protective lung ventilation group, VT will be set at 6 ml/kg of ideal body weight combined with individualized PEEP (PEEPx) during intraoperative dura mater opening, but in other periods of general anesthesia, VT will be set at 8 ml/kg of ideal body weight. Titration method of individualized PEEP (PEEPx) [1]: VT and respiratory rate will be fixed at 6ml/kg and 15 beats per minute during PEEP trial. Titration can only begin once the dura is opened. The titration for the individual PEEP can then be initiated by increasing PEEP from 2 to 10cm H2O incrementally. Each PEEP level (2, 3, 4, 5, 6, 7, 8, 9, 10cm H2O) will be maintained for 1 minute, and the pulmonary compliance of the last cycle will be recorded at each PEEP level. At last, the PEEP value at the highest compliance will be selected as the individual PEEP of patient. Regional cerebral oxygen saturation (rSO2), partial pressure of oxygen and carbon dioxide, oxygenation index, lactic acid level in arterial blood, and mean arterial pressure will be compared before anesthesia (T0), before dura opening (T1), after dura closing (T2) and 24 h after surgery (T3). Pulmonary ultrasound scores will be performed at T0 and T3.The degree of brain relaxation before and after protective lung ventilation will be evaluated by the surgeon using the brain relaxation scale. Amount of vasoactive drugs used and blood loss will be recorded during intraoperative dura mater opening. The total duration and secondary rate of surgery also will be recorded. Discussion: This study aims to determine whether intraoperative pulmonary protection strategy can improve regional cerebral oxygen saturation in patients undergoing intracranial tumor surgery, and to investigate whether intraoperative pulmonary protection strategy does not affect the degree of brain tissue swelling and the amount of blood loss during surgery. If our results are positive, this study will show that intraoperative pulmonary protection strategy can be used effectively and safely in neurosurgical patients undergoing craniotomy for tumor resection. Trial registration: chictr.org.cn, ID: ChiCTR1900025632. Registered on 3 September 2019. tudy protocol version 1.0.