Effects Of Different Inhalation Oxygen Concentrations Combined With Permissive Hypercapnia On Lung Injury And Early Postoperative Cognitive Dysfunction In Lobectomy Patients

Objective:To observe the effects of different inhalation oxygen concentrations（FiO₂）combined with permissible hypercapnia（PHC）on lung injury and early postoperative cognitive dysfunction in lobectomy patients,and to explore the optimal inhalation oxygen concentration after intraoperative combined permissible hypercapnia,in order to provide guidance for adjusting the respiratory settings during single lung ventilation.Method:Eighty patients who underwent pulmonary lobectomy in thoracic and cardiac surgery were selected,ASA classification I to III,aged 40 to 65years old,with Body Mass Index（BMI）ranging from 18 to 29kg·m^-2and gender no restriction.A 2*2*4（FiO₂*PaCO₂*time）mixed experimental design was used to study the effects of different FiO₂combined with PHC on lung injury and early postoperative cognitive dysfunction in patients.FiO₂and arterial carbon dioxide partial pressure（PaCO₂）were intergroup variables,and FiO₂was divided into 60%and 75%.PaCO₂can be divided into PaCO₂=35～45mm Hg（normal PaCO₂）and PaCO₂=50～70mm Hg（PHC）.In order to facilitate writing,this study will be represented by groups A,B,C and D.That is,FiO₂60%+normal PaCO₂（group A）,FiO₂60%+PHC（group B）,FiO₂75%+normal PaCO₂（group C）,FiO₂75%+PHC（group D）during single lung ventilation.Time was the variable in the group,which was divided into four time points,namely1min after intubation（T₁）,15min after single lung ventilation（T₂）,30min after single lung ventilation（T₃）and 60min after single lung ventilation（T₄）.Randomized number table method was used to evenly allocate patients to four groups,20 patients in each group,all of which were preoxygenated（100%oxygen）,then anesthesia induction,and ventilation with positive pressure.2 min after tracheal intubation,bilateral lung ventilation tidal volume 6～8 ml·kg^-1,respiratory rate 12～16 breaths/min,oxygen flow rate 2 L·min^-1,inspiration-expiration ratio 1:1.5～2,positive end-expiratory pressure（PEEP）5 cm H₂O.The inhaled oxygen concentration of group A and Group B was adjusted to 60%,and that of group C and group D was adjusted to 75%.PaCO₂in group A and group C was maintained at 35～45mm Hg by adjusting respiratory parameters.PaCO₂of group B and group D was adjusted to 50～70mm Hg by adjusting respiratory parameters.In single lung ventilation,all respiratory parameters remained unchanged.After the resumption of bilateral ventilation,PaCO₂of all patients was adjusted to normal by adjusting respiratory parameters.Airway pressure was maintained below 30cm H₂O during mechanical ventilation.During this process,mean arterial pressure（MAP）,heart rate（HR）,pulse oxygen saturation（Sp O₂）,FiO₂,partial pressure of end-expiratory carbon dioxide（Pet CO₂）,tidal volume（VT）,positive end-expiratory pressure（PEEP）,airway peak pressure（Ppeak）,BIS value of EEG dual frequency index were recorded at the four time points studied.Blood samples of radial artery and jugular vein balls were selected at four time points for blood gas analysis.According to the collected data,the arterial oxygen partial pressure（PaO₂）was recorded,and the dynamic lung compliance（Cdyn）,cerebral oxygen uptake rate（CE-RO₂）,ratio of cerebral blood flow to cerebral oxygen metabolic rate（CBF/CMRO₂）,oxygenation index（OI）and intrapulmonary flow separation rate（Qs/Qt）were calculated.Improved Murray lung injury scores at T₁and after surgery were recorded,and MMSE scores were recorded at preoperative,1day and 7 days postoperative.Result:79 cases were eventually included in this study（1 case was excluded due to single lung ventilation time less than 60min）:19 cases of FiO₂60%+normal PaCO₂（group A）,20 cases of FiO₂60%+PHC（group B）,20 cases of FiO₂75%+normal PaCO₂（group C）,20 cases of FiO₂75%+PHC（group D）.（1）Compared with T₃time points,PaO₂and PaO₂/FiO₂in groups A,B and C were increased at T₂and T₄time points（P<0.05）.（2）Compared with group A,MAP,HR,Cdyn,PaO₂,PaO₂/FiO₂and CBF/CMRO₂were increased in group B at T₂-T₄time points,while Ppeak and CE-RO₂were declined（P<0.05）.Compared with group C,the change trend of the above indexes in group D at time points T₂-T₄was the same as that in group A and Group B.（3）Compared with group A,PaO₂,Qs/Qt and CBF/CMRO₂in group C at time points T₂-T₄were increased,while CE-RO₂was declined（P<0.05）;Compared with group B,the change trend of the above indexes in group D at time points T₂-T₄was the same as that in group A and Group C.（4）Compared with group B,MMSE scores in groups A,C and D were declined 1 day after surgery,and improved Murray lung injury scores were increased after surgery（P<0.05）.（5）Compared with group A,Ppeak,Cdyn,PaO₂/FiO₂,MAP and HR in group C were no obvious variation at T₁-T₄time points（P>0.05）.Compared with group B,there were no obvious variation in the above indexes in group D at T₁-T₄time points（P>0.05）.Compared with group A,Qs/Qt of group B had no obvious variation at T₁-T₄time points（P>0.05）.Compared with group C,Qs/Qt of group D had no obvious variation at T₁-T₄time points（P>0.05）.Conclusion:During single-lung ventilation,oxygen inhalation concentration of60%combined with allowable hypercapnia（PCO₂=50～70mm Hg）decrease cerebral oxygen metabolism,reduce lung injury and the occurrence of early postoperative cognitive dysfunction.