The Effect Of Different Level Of PEEP On Cerebral Oxygen Saturation Of Elderly Patients During One Lung Ventilation

Background and Objective One lung ventilation is required in most thoracoscopic surgery in order to separate healthy lung from affected lung and to provide optimal condition for the surgery,which is accompanied with important physiological disturbances such as increased mechanical stress,increased pulmonary vascular resistance,and hypoxic pulmonary vasoconstriction?HPV?in the non-dependent lung.This leads to a pulmonary arteriovenous shunt of the deoxygenated blood,changes in alveolar– arterial oxygen tension,and activation of inflammatory processes.The influence of these changes on cerebral oxygenation during thoracic surgery with OLV has been studied in a preliminary study which found a significant decrease in cerebral saturation during OLV,seem to be correlated with postoperative complications.Reduced perioperative cerebral saturation correlates with greater morbidity and mortality in patients undergoing open heart surgery and major abdominal procedures.And also in patients following thoracic surgery.The important aspects of ventilator-induced lung injury?VILI?are volutrauma,barotrauma,atelectrauma,and oxygen toxicity.The lung protective ventilation strategy?LPV?,which addresses these issues by using a small VT with positive end-expiratory pressure?PEEP?,limited airway pressure,and low Fi O₂,has gainedwide acceptance as a ventilation strategy and has been shown to reduce VILI in patients with ARDS.Lung-protective ventilation strategies can reduce acute lung injury,but may promote alveolar collapse as a consequence of low tidal volume.Atelectasis prevention during LPV requires PEEP;however,optimal PEEP levels and actual effects of PEEP are controversial.Cerebral oximetry has been used to monitor cerebral oxygen saturation during cardiac,aortic arch,and abdominal surgeries and also during carotid endarteriectomy and neurosurgery.Since there is about three times more venous than arterial blood,near-infrared spectroscopy provides an instantaneous and continuous evaluation of the ratio between oxygen supply and demand in a delimited area of the frontal cortex.With the development of the society and the improvement of the living standard,there are more and more elderly patients in the operating room.The function of respiratory system is decreased with increasing age.At present,there are no reported studies of the effects of individualized PEEP settings titrated with a PEEP decrement trial on cerebral oxygen saturation in elderly patients during one-lung ventilation.We hypothesized that such a approach could improve cerebral oxygen saturation and lung mechanics compared with the establishment of a standardized 5 cm H₂ O PEEP after an alveolar recruitment maneuver during one-lung ventilation.We performed a prospective,randomized controlled trial to test this hypothesis.Methods Forty six patients with ASA ?-? who were scheduled for selected video-assisted thoracoscopic surgery were enrolled in this study.Forty-six patients aged between 65-75 were randomly allocated to the study or control group.During OLV,two different PEEP levels were implemented.Both groups received an alveolar recruitment maneuver at the beginning and end of one-lung ventilation.During one-lung ventilation,patients in the study group?S group,n=23?were ventilated with an individualized PEEP determined by a PEEP decrement titration trial,whereas the control group?C group,n=23?ventilated with a PEEP 5 cm H₂ O.Cerebral oxygensaturation,arterial blood samples,cardiac index,and lung mechanics were repeatedly measured throughout the surgery procedure.Results 1.Compared with the control group,there was no significantly difference between groups as to the general situation.2.Compared with the control group,rSO₂ and Pa O₂ were significantly increased in the study group.3.In both groups,static compliance decreased when bilateral-lung ventilation was switched to one-lung ventilation.After an alveolar recruitment maneuver,static compliance increased significantly in the study group and remained increased throughout one lung ventilation.4.Compared with T1,airway resistance increased in both groups at T2,and remained increased throughout one-lung ventilation,but no significant differences were found between groups.5.No differences in cardiac index between groups with different levels of PEEP.Conclusion During one-lung ventilation,the effects of an individualized level of PEEP based on a PEEP decrement trial with an alveolar recruitment is better on rSO₂ and lung function compared with that of simple arbitrary PEEP levels of 5 cm H₂O...