Selection Of The PEEP In ARDS Patients With COPD By EIT And The Effects Of Different PEEP Levels On Respiratory And Hemodynamic Function In ARDS Patients

BackgroundAcute Respiratory Distress Syndrome（ARDS）is a syndrome in which lung capillary endothelial cells and alveolar epithelial cells are damaged by a variety of reasons,with progressive hypoxemia and dyspnea as the main manifestations.Mechanical ventilation is the cornerstone of ARDS treatment.After the implementation of lung protection ventilation strategies,the disability rate and fatality rate of ARDS have been significantly reduced,but the current fatality rate is still as high as 35%-60%.Positive end expiratory pressure（PEEP）is an important part of lung protection ventilation strategy.It can improve Pa O₂/Fi O₂（P/F）and open partially collapsed alveoli and maintain the openness of the alveoli to reduce Ventilator-related lung injury（VILI）.The response of ARDS to PEEP treatment is quite different.Ventilation strategies adopted according to different types of ARDS can improve the prognosis of ARDS patients.Studies showed that 21%of ARDS patients have chronic obstructive pulmonary disease（COPD）.COPD is a type of obstructive lung disease characterized with small airway disease,reversible airflow limitation,over-inflated lung dynamics and gas trapped,and lung heterogeneity is more complicated in ARDS patient with CODP.When PEEP is used in mechanical ventilation,it will cause the risk of increased lung volume,over-expansion of alveoli,and decreased heart function.Over-inflated alveoli are also an important factor leading to VILI.There is controversy about the ventilation strategy of ARDS patients with COPD,especially the choice of PEEP,which may have a higher risk of potential adverse effects.Although there are many methods for titrating PEEP in clinical practice,none of them can better reflect the open and inflated state of the patient’s alveoli except for the CT method.Therefore,how to titrate PEEP in ARDS patients with COPD is still a clinical problem.Electrical impedance tomography（EIT）is a new method for evaluating the gas distribution in the lungs.Compared with the traditional ARDS net table method,the EIT method（gas distribution-oriented PEEP titration method）can monitor the gas distribution caused by ventilation in the lungs.Changes in internal impedance reflect changes in local lung tissue respiratory mechanics;compared with CT method,EIT method has the advantages of non-invasive,non-radiation and real-time monitoring at the bedside.EIT can be used to monitor the collapse,recruitment and over-expansion of local lung tissues.At present,EIT has been studied for the selection of PEEP during ventilation in patients with ARDS and COPD.However,there are very few studies on PEEP selection in ARDS patients with COPD.Therefore,we hypothesize that the PEEP level required for ventilation may be different between the COPD group（ARDS patients with COPD）and non-COPD group（ARDS patients without COPD）.In the COPD group,the PEEP level titrated by the EIT method was different from the traditional ARDS net method.There are differences in the response of the two groups of patients to PEEP levels,and the COPD group may be more difficult to tolerate high levels of PEEP.Objective1.Observe the difference in respiratory mechanics between the COPD group and the non-COPD group during ventilation.2.Apply the EIT method and ARDS net method to titrate the PEEP levels of the COPD group and the non-COPD group,and observe the gas exchange,respiratory mechanics,hemodynamics,and gas distribution under the PEEP levels titrated by the two methods,so as to find the appropriate PEEP selection method.3.Explore the effects of different PEEP levels on the breathing and circulation of the two groups of patients,and evaluate the benefits and risks of applying different PEEP levels.4.Provide a new option for the mechanical ventilation parameter setting of the COPD group.MethodsARDS patients requiring mechanical ventilation who were admitted to the Department of Critical Care Medicine of the First Affiliated Hospital of Guangzhou Medical University between August 2017 and December 2020.Patients who met the inclusion and exclusion criteria were divided into COPD group（ARDS patients with COPD）and no-COPD group（ARDS patients without COPD）.The first part1.The patient is fully sedated,analgesic and muscle relaxation.Arteriovenous catheters are established,and EIT is connected;mechanical ventilation mode:volume control mode,set tidal volume 6-8ml/kg（predicted body weight）,PEEP 5 cm H₂O,Pplat<30 cm H₂O,Fi O₂ is 100%.2.Then maintain Sp O₂ stable at 88-95%,select PEEP level according to Fi O₂/PEEP Lower PEEP table,this PEEP is the PEEP value of ARDS net method,and record the relevant parameters under this PEEP level,including respiratory mechanics and blood flow Parameters such as respiratory mechanics,gas distribution,gas exchange and oxygen delivery.3.Keep other ventilation parameters unchanged,adjust the PEEP level by 2-3 cm H₂O,obtain the global inhomogeneity index（GI）according to EIT monitoring,and the PEEP level corresponding to the minimum value（lowest point of the curve）,and record the PEEP level and related parameters.4.According to the PEEP level titrated by the EIT method and ARDS net method,analyze and compare the differences in respiratory mechanics,gas exchange and hemodynamics during ventilation at the two PEEP levels.The second part1.In the COPD group,the PEEP level titrated by the EIT method was ventilated for30 minutes,and other parameters were kept unchanged.The PEEP level was gradually increased from 0 cm H₂O-3 cm H₂O-5 cm H₂O-8 cm H₂O-10 cm H₂O-12 cm H₂O-14cm H₂O-16 cm H₂O,The interval of each adjustment is 30 minutes,and the parameters such as respiratory mechanics,hemodynamics,gas distribution,gas exchange and oxygen delivery are measured and calculated.Because the COPD group had a significantly increased risk of hemodynamics when the PEEP level was greater than 16 cm H₂O during the pre-experimental process,the PEEP level in this study was increased to 16 cm H₂O and no longer increased.2.In the non-COPD group,the PEEP level titrated by the EIT method was ventilated for 30 minutes,and other parameters were kept unchanged.The PEEP level gradually increased from 5 cm H₂O-8 cm H₂O-10 cm H₂O-12 cm H₂O-14 cm H₂O-16 cm H₂O-18 cm H₂O-20 cm H₂O Up-regulate PEEP,the interval of each adjustment is 30 minutes,after each adjustment of PEEP,all parameters under the PEEP are recorded,and the respiratory mechanics,hemodynamics,gas distribution,gas exchange and oxygen delivery parameters are measured and calculated.Because the PEEP level of patients without COPD in the pre-experimental process is less than 5 cm H₂O,the risk of SPO₂ is lower than 88%.In this study,the level of PEEP was not reduced to 0 cm H₂O and 3 cm H₂O.3.When the above 8 levels of PEEP adjustment is over,the experiment will end,adjust the ventilator parameters based on the patient’s comprehensive situation,and maintain mechanical ventilation therapy at the PEEP level titrated by the EIT method.4.Analyze and compare the effects of different PEEP levels on the breathing and circulation of the two groups of patients.ResultsThe first part of results1.Twenty-seven patients meet the criteria for inclusion and discharge,all of which are ARDS caused by severe pneumonia;among them,14 patients in the COPD group and13 patients in the non-COPD group.The P/F of the patients was 175.5±61.3 mm Hg,including 3 patients with severe ARDS,13 patients with moderate ARDS,and 11 patients with mild ARDS.The COPD group had higher PEEPi than the non-COPD group（5.8±2.1 cm H₂O VS 0.31±0.43 cm H₂O,P<0.001）;the EELV of the COPD group was significantly larger than that of the non-COPD group（1135±217.3 ml VS 724.6±130.8ml,P<0.001）.2.The level of PEEP titrated by the EIT method in the COPD group was lower than that in the non-COPD group（6.93±1.69 cm H₂O VS 12.15±2.40 cm H₂O P<0.001）.The PEEP level titrated by ARDS net in the COPD group was lower than that in the non-COPD group（10.43±1.20 cm H₂O VS 14.0±3.0 cm H₂O,P<0.001）.The PEEP level titrated by EIT method in COPD group was lower than ARDS net method（6.93±1.69 cm H₂O VS 10.43±1.20 cm H₂O P<0.001）.There was no difference between the PEEP level titrated by the EIT method and the ARDS net method in the non-COPD group（12.15±2.40 cm H₂O VS 14.0±3.0 cm H₂O,P=0.098）.In the COPD group,the GI under the PEEP level titrated by the EIT method was lower than the ARDS net method（0.397±0.040 VS 0.446±0.052 P=0.001）,and the difference was statistically significant.In the non-COPD group,there was no significant difference between the GI under the PEEP level titrated by the EIT method and the ARDS net method（0.450±0.038 VS 0.477±0.021 P=0.063）.3.1 In the COPD group,comparison of the patient’s respiratory mechanics parameters during ventilation under PEEP level titrated by EIT method and PEEP level titrated by ARDS net method.The peak airway pressure（Ppeak cm H₂O）of the EIT method was significantly lower than that of the ARDS net method（29.5±4.1 cm H₂O VS 33.64±5.19 cm H₂O P=0.001）,the difference was statistically significant;the airway plateau pressure（Pplat cm H₂O）of the EIT method was significantly lower than that of the ARDS net method（16.50±4.35 cm H₂O VS 20.93±5.37 cm H₂O）,P=0.001),the difference is statistically significant;the dead space ventilation ratio（Vd/Vt）of the EIT method is significantly lower than that of the ARDS net method（48.29±6.78%VS 55.14±8.85,P=0.001）,the difference is statistically significant;The ventilation ratio（VR）of the EIT method is lower than that of the ARDS net method（1.63±0.33 VS 1.87±0.33 P=0.001）,and the difference is statistically significant;the mechanical power（MP）of the EIT method is lower than that of the ARDS net method（13.92±2.18 J/min VS 15.87±2.53 J/min P=0.001）,the difference was statistically significant;The static compliance（Cst）of the EIT method is higher than that of the ARDS net method（42.61±13.77 ml/cm H₂O VS 38.39±13.86 ml/cm H₂O P=0.001）,and the difference is statistically significant;The end-expiratory lung volume（EELV）of the EIT method is smaller than that of the ARDS net method（1326±201.5 ml VS 1440±182.6 ml P=0.019）,the difference is statistically significant;Driving pressure（PD）were not significantly different,P>0.05.3.2 In the COPD group,comparison of gas exchange parameters during ventilation under PEEP level titrated by EIT method and PEEP level titrated by ARDS net method.Pa CO₂ of the EIT method was lower than that of the ARDS net method（54.07±6.78mm Hg VS 63.21±8.26 mm Hg,P=0.001）,the difference was statistically significant.There was no statistically significant difference among other parameters（including p H,P/F）,P>0.05.3.3 In the COPD group,comparison of hemodynamic parameters during ventilation under PEEP level titrated by EIT method and PEEP level titrated by ARDS net method.The cardiac index（CI）of the EIT method was higher than that of the ARDS net method（3.41±0.50 l/min/m²VS 3.02±0.43 l/min/m²,P=0.001）,the difference is statistically significant;The amount of norepinephrine in EIT method is lower than ARDS net method（0.105±0.077 ug/kg/min VS 0.119±0.076 ug/kg/min,P=0.022）,the difference is statistically significant;Other monitored hemodynamic parameters,such as central venous pressure（CVP）,mean arterial pressure（MAP）,heart rate（HR）were not statistically different,P>0.05.3.4 In the COPD group,the effect of PEEP level titrated by EIT method and PEEP level titrated by ARDS net method on the gas distribution in the lungs during ventilation;The proportion of ventilation between Z%ROI3（27.93±7.65 VS 33.07±10.57,P=0.027）and Co V（36.0±10.69 VS 42.21±11.78,P=0.005）of the EIT method was lower than that of the ARDS net method,and the difference was statistically significant;Z%ROI1,Z%ROI2,,and Z%ROI4 were no statistical difference between these methods,P>0.05.3.5 In the COPD group,comparison of oxygen metabolism during ventilation between PEEP level titrated by EIT method and PEEP level titrated by ARDS net method.The oxygen delivery（DO₂）of the EIT method was higher than that of the ARDS net method（466.40±71.08 ml/min/m²vs 411.10±69.71 ml/min/m²,P=0.001）,the difference was statistically significant,while the central venous oxygen saturation（Scv O₂）was not statistically different,P>0.05.The second part of the results1 The effect of different PEEP levels on gas exchange,respiratory mechanics and gas distribution in the two groups1.1 With the increase of PEEP level,the P/F of the two groups of patients gradually increased（P<0.001,P<0.001）.When the PEEP level of the COPD group exceeded 14cm H₂O,the patient’s P/F could not continue to increase significantly（281.00±88.78mm Hg VS 273.00±77.48 mm Hg,P=0.155）.There was no significant difference in P/F between the two groups of patients at different levels of PEEP（P>0.05）.1.2 With the increase of PEEP level,the EELV of the two groups of patients gradually increased（P<0.001,P<0.001）.The EELV of the COPD group was higher than that of the COPD group（PEEP 5 cm H₂O,8 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,P<0.001）,the difference was statistically significant.1.3 With the increase of PEEP level,the ventilation in the dorsal lung area（Z%ROI14）increased and the ventilation in the ventral lung area（Z%ROI1）decreased（P<0.001,P<0.001）.Under PEEP 5 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,the Z%ROI4 of the COPD group was higher than that of the non-COPD group（P=0.022,P=0.028,P=0.023,P=0.025,P=0.024）,the difference was statistically significant.Under PEEP 8 cm H₂O,there was no significant difference in Z%ROI4between the COPD group and the non-COPD group（P>0.05）.Under PEEP 5 cm H₂O,8cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,Z%ROI1 was not statistically different between the COPD group and the non-COPD group（P>0.05）.1.4 The level of PEEP increased.The level of PEEP in the COPD group increased from 0 cm H₂O to 5 cm H₂O,the lung compliance of patients in the COPD group increased（P<0.001）.After more than 5 cm H₂O,the lung compliance of patients gradually decreased（P=0.001）.In the non-COPD group,with the increase of PEEP level,the compliance of patients did not decrease significantly（P=0.331）,and the difference was not statistically significant.Under PEEP 5 cm H₂O,the lung compliance of the COPD group was higher than that of the non-COPD group（P=0.020）,and the difference was statistically significant.Under PEEP 8 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16cm H₂O,there was no significant difference in lung compliance between the COPD group and the non-COPD group（P>0.05）.1.5 With the increase of PEEP level,the driving pressure in the COPD group gradually increased（P<0.001）,and the difference was statistically significant;the change in driving pressure in the non-COPD group was not statistically significant（P=0.336）.Under PEEP 5 cm H₂O,the driving pressure of the COPD group was higher than that of the non-COPD group（P=0.025）,and the difference was statistically significant.At other PEEP levels（8 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O）,there was no significant difference in driving pressure between the COPD group and the non-COPD group（P>0.05）.1.6 With the increase of PEEP level,the VR of the COPD group and the non-COPD group gradually increased（P<0.001,P=0.004）.Under PEEP 10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,the VR of the COPD group was higher than that of the non-COPD group（P=0.018,P=0.026,P=0.005,P<0.001）,the difference was statistically significant significance.Under PEEP 5 cm H₂O and 8 cm H₂O,there was no significant difference in VR between the COPD group and the non-COPD group（P>0.05）.1.7 With the increase of PEEP level,the MP of the COPD group and the non-COPD group gradually increased（P<0.001,P=0.004）.Under PEEP 5 cm H₂O,8 cm H₂O,10cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,the MP of the COPD group was higher than that of the non-COPD group（P<0.001,P=0.002,P=0.005,P=0.025,P=0.012,P=0.026）,the difference is statistically significant.2 The effect of different PEEP levels on the hemodynamics of the two groups of patients2.1 With the increase of PEEP level,the CI of the two groups of patients gradually decreased（P<0.001,P=0.005）,and the CI of the COPD group decreased more significantly.Under PEEP 10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,the COPD group had low CI than non-COPD group（P=0.035,P=0.009,P<0.001,P<0.001）,the difference was statistically significant.Under PEEP 5 cm H₂O and 8 cm H₂O,there was no significant difference in CI between the COPD group and the non-COPD group（P>0.05）.2.2 With the increase of PEEP level,the CVP of the two groups of patients gradually increased（P<0.001,P=0.001）.Under PEEP 10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,the CVP of the COPD group was higher than that of the non-COPD group（P=0.018,P=0.004,P=0.001,P<0.001）,and the difference was statistically significant.Under PEEP 5 cm H₂O and 8 cm H₂O,there was no significant difference in CVP between the COPD group and the non-COPD group（P>0.05）.2.3 and 2.4 With the increase of PEEP level,there was no statistical difference between the MAP and NE applied in the COPD group and the non-COPD group（P>0.05）.Under PEEP 5 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,there was no significant difference in MAP and the amount of NE applied between the two groups of patients（P>0.05）.2.5 With the increase of PEEP level,the IAP of the two groups of patients gradually increased（P<0.001,P<0.001）.Under PEEP 5 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,16 cm H₂O,there was no significant difference in IAP between the COPD group and the non-COPD group（P>0.05）.3 The effect of different PEEP levels on oxygen delivery in the two groupsWith the increase of PEEP level,the DO₂ of the two groups of patients gradually decreased（P<0.001,P=0.020）.Under PEEP 5 cm H₂O,8 cm H₂O,10 cm H₂O,12 cm H₂O,14 cm H₂O,there was no significant difference in DO₂ between the COPD group and the non-COPD group（P>0.05）.Under PEEP 16 cm H₂O,the DO₂ of the COPD group was lower than that of the non-COPD group（P=0.013）.Compared with the non-COPD group,as the PEEP level increased,the COPD group had a more significant decline in oxygen delivery.Conclusion1.The PEEPi of the COPD group（ARDS patients with COPD）was higher than that of the non-COPD group（ARDS patients without COPD）,and the end-expiratory lung volume of the COPD group was significantly higher than that of the non-COPD group.The titrated PEEP level of the COPD group was lower than that of the non-COPD group.2.In the COPD group,the PEEP level titrated by the EIT method was lower than the ARDS net method,and it helped to improve the VR,MP,CI and DO_2,and had less adverse effects on cardiac function.The EIT method is feasible for the PEEP titration of the COPD group.3.With the level of PEEP increases,the improvement of P/F in ARDS patients increases which may be related to the increase in end-expiratory lung volume and the increase in the proportion of ventilation in the dorsal lung area.Compared with the non-COPD group,with the increase of PEEP level,the VR and MP of the COPD group increased more significantly,and the lung compliance,CI,and DO₂ decreased more significantly.As the level of PEEP increases,the potential adverse risk of PEEP to the COPD group may be higher.