A novel positive end-expiratory pressure titration using electrical impedance tomography in spontaneously breathing acute respiratory distress syndrome patients on mechanical ventilation: an observational study from the MaastrICCht cohort

Abstract

There is no universally accepted method for positive end expiratory pressure (PEEP) titration approach for patients on spontaneous mechanical ventilation (SMV). Electrical impedance tomography (EIT) guided PEEP-titration has shown promising results in controlled mechanical ventilation (CMV), current implemented algorithm for PEEP titration (based on regional compliance measurements) is not applicable in SMV. Regional peak flow (RPF, defined as the highest inspiratory flow rate based on EIT at a certain PEEP level) is a new method for quantifying regional lung mechanics designed for SMV. The objective is to study whether RPF by EIT is a feasible method for PEEP titration during SMV. Single EIT measurements were performed in COVID-19 ARDS patients on SMV. Clinical (i.e., tidal volume, airway occlusion pressure, end-tidal CO₂) and mechanical (cyclic alveolar recruitment, recruitment, cumulative overdistension (OD), cumulative collapse (CL), pendelluft, and PEEP) outcomes were determined by EIT at several pre-defined PEEP thresholds (1-10% CL and the intersection of the OD and CL curves) and outcomes at all thresholds were compared to the outcomes at baseline PEEP. In total, 25 patients were included. No significant and clinically relevant differences were found between thresholds for tidal volume, end-tidal CO₂, and P0.1 compared to baseline PEEP; cyclic alveolar recruitment rates changed by -3.9% to -37.9% across thresholds; recruitment rates ranged from - 49.4% to + 79.2%; cumulative overdistension changed from - 75.9% to + 373.4% across thresholds; cumulative collapse changed from 0% to -94.3%; PEEP levels from 10 up to 14 cmH₂O were observed across thresholds compared to baseline PEEP of 10 cmH₂O. A threshold of approximately 5% cumulative collapse yields the optimum compromise between all clinical and mechanical outcomes. EIT-guided PEEP titration by the RPF approach is feasible and is linked to improved overall lung mechanics) during SMV using a threshold of approximately 5% CL. However, the long-term clinical safety and effect of this approach remain to be determined.

Keywords: ARDS; Airway occlusion pressure; Electrical impedance tomography; Pendelluft; Positive end-expiratory pressure; Regional peak flow; Spontaneous ventilation.

Fig. 1

Measurement protocol for the SMV population. During the EIT measurement, only the PEEP-level is adjusted, while other respiratory settings (i.e., pressure support, slope and oxygen fraction) remain unchanged. EIT: electrical impedance tomography; PEEP: positive end-expiratory pressure; P0.1: airway occlusion pressure; SpO₂: peripheral oxygen saturation

Fig. 2

Example of determining optimal positive end-expiratory pressure based on two pre-defined thresholds: 5% cumulative collapse and the intersection of the cumulative overdistension rate and cumulative collapse rate curves. The grey dashed line represents the 5% cumulative collapse rate threshold. For this approach a positive end expiratory pressure level of 10 is chosen, since its cumulative collapse rate value is closest and under the 5% cumulative collapse rate of all positive end expiratory pressure levels during the decremental trial. An identical approach is used for the 1–4% and 6–10% cumulative collapse threshold. The intersection of the cumulative collapse and cumulative overdistension is considered the positive end expiratory pressure level, where the difference between the cumulative overdistension rate and cumulative collapse rate is the lowest. In this example, the intersection is found at a positive end expiratory pressure level of 12 (black dashed rectangle). CL: cumulative collapse rate; OD: cumulative overdistension rate; PEEP: positive end expiratory pressure

Fig. 3

Median clinical outcomes at the PEEP determined by the pre-defined thresholds and at baseline PEEP. The repeated measures ANOVA results are showed per variable. If a significant outcome is found in the repeated measures ANOVA, post hoc analysis with Bonferroni correction is visualized for each pre-defined threshold and baseline. Significant differences in the post hoc analysis are colored red. ANOVA: analyses of variances; CL: cumulative collapse rate; etCO₂: end-tidal carbon dioxide; Inters.: intersection of cumulative overdistension and collapse curves; P0.1: airway occlusion pressure; PEEP: positive end-expiratory pressure; TV: tidal volume per kilogram of predicted body weight

Fig. 4

Median mechanical outcomes at the PEEP determined by the pre-defined thresholds and at baseline PEEP. The Friedman test results are showed per variable. If a significant outcome is found in the Friedman test, post hoc analysis with Bonferroni correction is visualized for each pre-defined threshold and baseline. Significant differences in the post hoc analysis are colored red. ANOVA: analyses of variances; CAR: Cyclic alveolar recruitment; CL: cumulative collapse rate; Inters.: intersection of cumulative overdistension and collapse curves; Recr.: Recruitment rate

Fig. 5

Median mechanical outcomes at the PEEP determined by the pre-defined thresholds and at baseline PEEP. The Friedman test results are showed per variable. If a significant outcome is found in the Friedman test, post hoc analysis with Bonferroni correction is visualized for each pre-defined threshold and baseline. Significant differences in the post hoc analysis are colored red. CL: cumulative collapse rate; etCO₂: end-tidal carbon dioxide; Inters.: intersection of cumulative overdistension and collapse curves; OD: cumulative overdistension rate; P0.1: airway occlusion pressure; PEEP: positive end-expiratory pressure; TV: tidal volume per kilogram of predicted body weight