Impact of PEEP Trials on Ventilation-Perfusion Matching in ARDS Patients

In the treatment of critically ill patients, mechanical ventilation is a key link, and appropriate mechanical ventilation strategies can open the alveoli and improve oxygenation, while inappropriate mechanical ventilation can increase lung injury and seriously affect the prognosis. Ventilator-related lung injury is mainly concentrated in barotrauma, volumetric injury, shear injury, and biological injury, and the monitoring of respiratory ventilation to the level of local ventilation can help to better assess the state of alveolar opening and alveolar collapse, and help to understand the uniformity of gas distribution in the lungs, which is closely related to lung injury. However, how to achieve simple, bedside and real-time lung ventilation and lung volume assessment in clinical work has always been a difficult problem to be overcome. This study intends to explore the changes of local ventilation and blood flow in the lungs during PEEP trail in patients with ARDS monitored by EIT.

Development and Clinical Application of EIT-based Pulmonary Blood Flow Imaging in Monitoring PEEP Trial Strategies for ARDS Patients: A Prospective Study

Background and Significance:

Mechanical ventilation is a crucial component in the treatment of critically ill patients. While mechanical ventilation strategies can improve oxygenation through alveolar recruitment, inappropriate ventilation can exacerbate lung injury and worsen outcomes.

Current monitoring methods for assessing pulmonary ventilation distribution, such as bedside chest radiography, CT scanning, and lung ultrasound, have limitations including radiation exposure, intermittent nature of assessment, and impracticality for continuous monitoring. Electrical impedance tomography (EIT) offers a promising solution as a radiation-free, real-time bedside monitoring tool that can assess regional ventilation distribution, lung volume, and respiratory mechanics.

Research Objectives:

The primary objective of this study is to investigate changes in regional ventilation-perfusion relationships during PEEP trials in ARDS patients using EIT monitoring. the investigators aim to develop and validate EIT-based pulmonary blood flow imaging techniques and evaluate their utility in guiding mechanical ventilation strategies.

Methods:

This prospective observational study will be conducted at the Department of Critical Care Medicine, Shanghai Jiao Tong University School of Medicine Affiliated Ruijin Hospital between July 2022 and July 2025. The investigators will enroll patients meeting ARDS criteria who require mechanical ventilation. The study will utilize the Dräger EIT device, which has over a decade of clinical application history and established data acquisition protocols.

Intervention Description： First phase: Observational study using EIT monitoring for lung ventilation and blood flow assessment without altering clinical management.

Second phase: Comparing impact of EIT-guided versus standard ventilation strategies on ARDS patient outcomes.

PEEP Trial Protocol:

Patients will undergo standardized PEEP trials with the following parameters:

* FiO2 will be adjusted to 100%
* Volume-controlled mode with respiratory rate of 12 breaths/minute
* I:E ratio of 1:1
* Tidal volume of 6 mL/kg predicted body weight
* PEEP levels of 0, 5, 10,15 and 20 cmH2O, each maintained for 2 minutes
* Continuous hemodynamic monitoring during PEEP trials
* Safety limits: Peak pressure not exceeding 45 cmH2O
* Immediate pressure reduction if peak pressure exceeds 40 cmH2O after 2 minutes

Data Collection:

The investigators will record:

* Baseline vital signs including heart rate, blood pressure, SpO2, respiratory rate
* EIT ventilation parameters including EELI, GI index, and ROI analysis
* EIT perfusion parameters including V/Q ratio, dead space percentage, and shunt fraction
* Continuous hemodynamic monitoring during PEEP trials
* Arterial blood gas analyses at defined time points

Outcome Measures:

Primary outcomes:

* Changes in regional ventilation-perfusion matching during PEEP trials
* Correlation between EIT-derived parameters and clinical outcomes

Secondary outcomes:

* Development of standardized EIT-based pulmonary blood flow monitoring protocols
* Establishment of PEEP titration guidelines based on V/Q matching

Statistical Analysis:

Sample size calculation is based on expected changes in EELI parameters, with α=0.05 and β=0.1. Data will be analyzed using repeated measures analysis for trends in EIT parameters across different PEEP levels. Multiple regression analysis will be used to evaluate relationships between EIT parameters and clinical outcomes.

Expected Impact:

This study aims to advance our understanding of regional ventilation-perfusion relationships in ARDS patients and develop more precise, individualized mechanical ventilation strategies. The findings may lead to improved patient outcomes through better-guided PEEP titration and ventilation management based on real-time EIT monitoring of both ventilation and perfusion parameters.

Eligibility Criteria:
Inclusion Criteria:

* Patients who meet the Berlin definition of ARDS and have been treated with mechanical ventilation (clinical diagnosis of ARDS by the attending ICU physician)

Exclusion Criteria:

* Age\< 18 or \>90 years