Background Electrical impedance tomography (EIT) visualises alveolar overdistension and alveolar collapse and enables optimisation of ventilator settings by using the best balance between alveolar overdistension and collapse (ODCL). Besides, the global inhomogeneity index (GI), measured by EIT, may also be of added value in determining PEEP. Optimal PEEP is often determined based on the best dynamic compliance without EIT at the bedside. This study aimed to assess the effect of a PEEP trial on ODCL, GI and dynamic compliance in patients with and without ARDS. Secondly, PEEP levels from “optimal PEEP” approaches by ODCL, GI and dynamic compliance are compared. Methods In 2015–2016, we included patients with ARDS using postoperative cardiothoracic surgery patients as a reference group. A PEEP trial was performed with four consecutive incremental followed by four decremental PEEP steps of 2 cmH2O. Primary outcomes at each step were GI, ODCL and best dynamic compliance. In addition, the agreement between ODCL, GI, and dynamic compliance was determined for the individual patient. Results Twenty-eight ARDS and 17 postoperative cardiothoracic surgery patients were included. The mean optimal PEEP, according to best compliance, was 10.3 (±2.9) cmH2O in ARDS compared to 9.8 (±2.5) cmH2O in cardiothoracic surgery patients. Optimal PEEP according to ODCL was 10.9 (±2.5) in ARDS and 9.6 (±1.6) in cardiothoracic surgery patients. Optimal PEEP according to GI was 17.1 (±3.9) in ARDS compared to 14.2 (±3.4) in cardiothoracic surgery patients. Conclusions Currently, no golden standard to titrate PEEP is available. We showed that when using the GI, PEEP requirements are higher compared to ODCL and best dynamic compliance during a PEEP trial in patients with and without ARDS.

Background: Spontaneous breathing efforts during mechanical ventilation are a widely accepted weaning approach for acute respiratory distress syndrome (ARDS) patients. These efforts can be too vigorous, possibly inflicting lung and diaphragm damage. Higher positive end expiratory pressure (PEEP) levels can be used to lower the magnitude of vigorous breathing efforts. Nevertheless, PEEP titrating tools are lacking in spontaneous mechanical ventilation (SMV). Therefore, the aim is to develop an electrical impedance tomography (EIT) algorithm for quantifying regional lung mechanics independent from a stable plateau pressure phase based on regional peak flow (RPF) by EIT, which is hypothetically applicable in SMV and to validate this algorithm in patients on controlled mechanical ventilation (CMV). Methods:The RPF algorithm quantifies a cumulative overdistension (OD RPF ) and collapse (CL RPF ) rate and is validated in a prospective cohort of mechanically ventilated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) patients on CMV. OD RPF and CL RPF are compared with compliance-based cumulative overdistension (OD P500 ) and collapse (CL P500 ) rates from the Pulmovista 500 EIT device at multiple PEEP levels (PEEP 10 cmH 2 O to PEEP 24 cmH 2 O) in EIT measurements from CMV patients by linear mixed models, Bland-Altman analysis and intraclass correlation coefficient (ICC).Results: Seventy-eight patients were included. Linear mixed models revealed an association between OD RPF and OD P500 of 1.02 (0.98-1.07, P<0.001) and between CL RPF and CL P500 of 0.93 (0.80-1.05, P<0.001).ICC values ranged from 0.78 to 0.86 (P<0.001) for OD RPF and OD P500 and from 0.70 to 0.85 (P<0.001) for CL RPF and CL P500 (PEEP 10 to PEEP 24). The mean bias between OD RPF and OD P500 in these PEEP levels ranged from 0.80% to 4.19% and from −1.31% to 0.13% between CL RPF and CL P500 .Conclusions: A RPF approach for quantifying regional lung mechanics showed a moderate to good agreement in coronavirus disease 2019 (COVID-19) related ARDS patients on CMV compared to the compliance-based approach. This, in addition to being independent of a plateau pressure phase, indicates that the RPF approach is a valid method to explore for quantifying regional lung mechanics in SMV.

Electrical impedance tomography (EIT) visualises alveolar overdistension (OD) and collapse (CL) and enables optimisation of ventilator settings by using the best balance between OD and Cl (ODCL). Besides, the global inhomogeneity index (GI), measured by EIT, may also be of added value in determining PEEP. PEEP is determined based on the best dynamic compliance (Cdyn) without EIT. This study aimed to assess the effect of a PEEP trial on ODCL, GI and Cdyn in patients with and without ARDS. Secondly, PEEP levels from “optimal PEEP” approaches by ODCL, GI and Cdyn are compared. In 2015–2016, we included patients with ARDS using postoperative cardiothoracic surgery (CTS) patients as a reference group. A PEEP trial was performed with four consecutive incremental followed by four decremental PEEP steps of 2 cmH2O. Primary outcomes at each step were GI, ODCL and Cdyn. In addition, the agreement between ODCL, GI, and Cdyn was determined for the individual patient. 28 ARDS and 17 CTS patients were included. The mean optimal PEEP, according to Cdyn, was 10.3 (± 2.9) cmH2O in ARDS compared to 9.8 (± 2.5) cmH2O in CTS patients. Optimal PEEP according to ODCL was 10.9 (± 2.5) in ARDS and 9.6 (± 1.6) in CTS patients. Optimal PEEP according to GI was 17.1 (± 3.9) in ARDS compared to 14.2 (± 3.4) in CTS. Currently, no golden standard to titrate PEEP is available. We showed that when using the GI, PEEP requirements are higher compared to ODCL and Cdyn during a PEEP trial in patients with and without ARDS.