Research On The EIT Monitoring In ARDS During PEEP Titration

Acute respiratory distress syndrome（ARDS）is a common cause of respiratory failure in critically ill patients,which is characterized by its intractable hypoxemia and high mortality.As the primary adjuvant therapy of ARDS,the main effect of mechanical ventilation（MV）is to improve the pulmonary ventilation directly.Application of appropriate positive end-expiratory pressure（PEEP）can improve oxygenation and accelerate lung tissue repair.But the incorrect PEEP will lead to ventilator associated lung injury（VALI）.Therefore,it is of great clinical significance in ARDS to setting appropriate PEEP value according to the monitoring state of ventilation for the purpose of avoiding VALI.The common clinical detection methods such as X-ray and CT are able to evaluate the lung injury effectively.However,such devices cannot be employed in dynamic detection and real-time evaluation due to radiation and other reasons.And clinical monitoring methods,like arterial blood gas analysis and mechanical parameters,can not provide lung local function information of ventilation.Therefore,in order to realize dynamic evaluation of local lung during mechanical ventilation and reduce the incidence of VALI in ARDS patients,a functional imaging technology,which can monitor ventilation information of the lung and help to adjust the ventilation strategy at bedside,is required.As a functional imaging technique,electrical impedance tomography（EIT）is dynamic,rapid,non-radioactive,low-cost and easy to operate.EIT can provide sufficient local information through continuous real-time monitoring of pulmonary ventilation at bedside.Currently,clinical studies on pulmonary EIT mainly focus on pulmonary function testing,monitoring of pulmonary perfusion and mechanical ventilation.There is still no uniform standard for EIT monitoring of ARDS mechnical ventilation.At the meantime,the existing functional EIT（fEIT）images and indices cannot directly reflect the evolution process of VALI.The research on abroad in EIT monitoring ARDS area is initial starting and domestic research is still relatively weak at present.Therefore,based on the review of domestic and foreign ARDS and EIT research reports,we carried out a series of studies on EIT experimental platform construction,software modular design,signal processing,feature EIT indices extraction,animal ARDS model experiments and clinical trials.The research contents of this study are as follows:（1）Establishment of EIT experimental platform and data processing methodsBased on available EIT hardware data acquisition system,the software platform for EIT monitoring ARDS mechanical ventilation was developed.The data post-processing platform is stable and easy-to-use,with functions of auxiliary monitoring,functional information analysis,one-dimensional curve and two-dimensional image display and indices extraction.In this section,the data preprocessing method as well as EIT indices extraction methods were established.Expiration time constant of EIT index τ_pixel was optimized and a controlled study on healthy people and COPD was conducted using this index.The results showed that there was a strong correlation（r=0.773）between （?） and the volume expiratory time constant;（?） could significantly distinguish the COPD patients from the healthy group（p<0.05）and increased with the severity.The conclusion is that （?） index provides a new idea for lung ventilation monitoring in ARDS from the physiological and physical perspective of lung unit expiratory capacity.Furthermore,it is a new index for PEEP setting of mechanical ventilation.（2）Clinical and trial study of PEEP titration in ARDS piglet model monitored by EITIn this section,the monitoring experimental study of recruitment maneuver（RM）and PEEP titration using EIT was carried out.PEEP guided by EIT indices were compared with routine method C_dyn.The ARDS model（n=9）of piglets were prepared by intravenously infusing oleic acid.Three recruiment manoeuvers,incremental PEEP（IP）,pressure control ventilation（PCV）and sustained insufflation（SI）followed PEEP titration were implemented.PEEP titration was performed from PEEP 20 cmH₂O to 0 cmH₂O every 2 cmH₂O with EIT monitoring synchronously.Mechanical ventidation parameters such as dynamic compliance were recorded.GI,OD_CL and （?） were calculated to evaluate the lung ventilation distribution homogeneity,the degree of overdistention（collapse）and the expiratory time constant.The result showed that EIT technology provided a 2D visual image for the PEEP setting of ARDS piglet model in this experiment compared with the traditional C_dynyn method.EIT indices used to monitor the RM process could provide convenience for finding the appropriate PEEP value in titration.The （?） index was closer to the results of C_dyn-guided PEEP compared with other EIT indices.（3）Experimental study on PEEP titration using EIT in post-operative cardiac surgery ARDS patientsARDS patients after cardiac surgery（n=11）were in enrolled and implemented PEEP titration monitored by EIT.The driving pressure of mechanical ventilation was constant at15 cmH₂O.RM and PEEP titration were performed by IP method.Pulmovista 500 system was used for monitoring.PEEP values guided by EIT indices（GI、OD_CL、（?））were compared to C_dyn.EIT image results were compared with clinical CT images.It turned that patients with C_dyn-guided PEEP showed significant improvement in lung dynamic compliance and oxygenation index at 4h and 8h after PEEP titration.There were no significant difference in PEEP settings by EIT methods and C_dyn method.Imaging contrast showed that the abnormal area of local pulmonary ventilation on the EIT functional image was consistent with the CT image.The EIT technique was equipped to dynamically monitor the local pulmonary ventilation and precaution the occurrence of VALI.In sum,this study has established EIT mechanical ventilation monitoring experimental platform with appropriate data preprocessing and indices extraction methods.The expiratory time constant index was optimized and was verified by experiments.PEEP titration in ARDS piglet model and clinical patients monitored by EIT were carried out respectively.Compared with the C_dyn method,the potential application of EIT indices in PEEP setting was verified.The innovations of this study are as follows:1)Series experimental studies of setting PEEP value guided by EIT in ARDS with MV are performed.The method of applying EIT monitoring on RM and PEEP titration in ARDS is established.2)The EIT expiratory time constant index is optimized,which lays a foundation for reflecting lung unit exhalation ability,abnormal pulmonary ventilation area and provides a reference for early warning of the VALI occurrence.