Electrical Impedance Tomography Monitors Gas Distribution In The Lungs During Prone Position In Patients With Acute Respiratory Distress Syndrome

Background:Acute respiratory distress syndrome(ARDS)is a clinical syndrome characterized by refractory hypoxemia caused by a variety of causes,with high severe and case fatality rates.At the same time,ARDS can be caused by a variety of both internal and external pulmonary factors,heterogeneity,no specific treatment drugs,it is recognized that the main treatment is to maintain the patient life through mechanical ventilation and lung protective ventilation strategy,mainly includes small tidal volume(VT)ventilation,limit platform pressure(pplat)<30cmH2o,limit driving pressure<15 cmH2O,positive end-expiratory pressure(PEEP),early prone position ventilation(PPV),early application of muscle drugs and extracorporeal membrane oxygenation treatment.The PPV in lung protective ventilation is simple,economical and suitable for clinical application.At present,there have been a large number of studies to prove that PPV can promote collapsed alveolar opening,uniform gas distribution in the lung,improve oxygenation,reduce lung injury,and reduce mortality in patients.Chinese guidelines recommend the early use of PPV in patients with moderate/severe ARDS,with each treatment time more than 12 hours/day,during which the treatment effect can be evaluated by monitoring changes in arterial oxygen partial pressure and carbon dioxide.However,some studies have shown that the improvement of oxygenation has no obvious correlation with the mortality,and the influencing factors of the change of carbon dioxide partial pressure are complex and are not special.At the same time,the traditional indicators such as Ppeak、Pplat、Pdriving and which reflect the overall situation cannot well explain the occurrence of local Ventilator Induced Lung Injury(VILI).Electric impedance imaging(EIT)can provide real-time monitoring of gas and blood flow distribution in the lung at the bedside,provide the heterogeneity of regional tidal volume,ventilation distribution,lung perfusion,cardiac output and cardiovascular volume status,and have high consistency with computed tomography(CT)in the evaluation of normal lung and lung injury.Currently EIT has been used to monitor and evaluate the therapeutic effect of PPV.Objective:In this study,by comparing the vital signs,Ppeak,Pptat,Pdriving,arterial blood gas analysis and EIT monitoring results before and after PPV,study the physiological changes of different time points before and after PPV,compare the correlation between common clinical indicators and EIT monitoring results,provide a new method for the efficacy evaluation of PPV efficacy,and finally compare the clinical differences of the respiratory mechanics,arterial blood gas and EIT indicators of the Dead and surviving patients.Methods:This is a single-center prospective physiological study,ARDS patients who received PPV treatment in Intensive Care Unit(ICU)of The First Affiliated Hospital of Guangzhou Medical University from February 19,2022 to September 19,2022 were selected as subjects.Their gender,age,height,weight,BMI,APACHE Ⅱ score and SOFA score,systolic and diastolic blood pressure,mean arterial pressure,heart rate,VT,Ppeak、Pplat、Pdriving,and other basic information were collected.All patients underwent a lung protective ventilation strategy,turning back in the supine position and being taken in the semireclining position.Experiments were performed at six different time points,including SPV,2rd hour after PPV,6th hour after PPV,12th hour after PPV,2rd hour after SPV,and 6th hour after SPV.At each time point,vital signs,VT、Ppeak、Pplat、Pdriving were recorded,and arterial blood was drawn for blood gas analysis,while EIT data was recorded,and the gas distribution and reversion were assessed by analyzing △End-expiratory Lung Impedance(EELI),Center of ventilation(COV),Global inhomogeneity(GI)index and Regional ventilation delay(RVD)%.Finally,the patients were divided into two groups according to death and survival,and the differences of the appeal indicators were compared respectively.Results:A total of 16 ARDS patients who were treated with PPV in ICU of the First Affiliated Hospital of Guangzhou Medical University from 2022 to September 19,2022,with a total of 29 PPV times,were enrolled in this study.There was no significant difference in respiratory rate,heart rate and mean arterial pressure before and after PPV;no significant change in PH,and oxygenation index improved at the 6th and 12th hours after PPV compared with pretreatment,and gradually increased with the extension of PPV time(173.6±75.3 vs.202.7±68.11 vs.227.2±81.7),but the improvement was not obvious in the early period(within 2 hours)(p<0.05).During PPV,△EELI continued to increase and reached the optimal level at 12th hours,but it cannot be denied that this effect would exceed 12 hours and remain better than before treatment within 6 hours of SPV(p<0.05),without no significant change in RVD%,GI index,and COV.The oxygenation index showed a positive weak correlation with COV(r=0.2498,p<0.05),a negative weak correlation with RVD%(r=-0.1775,p<0.05),and no significant linear correlation with GI index and△EELI.Compared with blood gas analysis and respiratory mechanical indicators,EIT monitoring can be more confirmed in the early stage,and with the extension of PP time,the gas distribution in the lung gradually improves,and the collapsed alveoli show continuous reversion,and the prolonged treatment time of PPV time may have greater clinical benefit.In Surviving patients,both Pplat and Pdri were lower than the Dead group(p<0.001),the oxygenation was significantly higher than the Surviving group,and continued to improve with prolonged prone positioning time(p<0.05),while the improvement in oxygenation was not significant in the dead group.In both the Death and Survival groups,PPV tended to decrease ventral EELI and increase dorsal EELI,and dorsal EELI was more pronounced the Dead group,but not statistically.Conclusions:Prone Position Ventilation can improve patient oxygenation and promote dorsal alveolar enlargement,and prolonging the time of prone position can further increase the effect of prone position.The EIT allows early detection of alveolar overdistension and excessive expansion,and a better clinical outcome may be associated with a reduction in VILI.In addition,this trial encourages clinicians to re-titrate PEEP during PPV to reduce overdistension,but further studies are still needed.