The incidence and interpretation of large differences in EIT-based measures for PEEP titration in ARDS patients

Abstract

Positive end-expiratory pressure (PEEP) can be titrated by electrical impedance tomography (EIT). The aim of the present study was to examine the performance of different EIT measures during PEEP trials with the aim of identifying "optimum" PEEP and to provide possible interpretations of largely diverging results. After recruitment (maximum plateau pressure 35 cmH 2 O), decremental PEEP trial with steps of 2 cmH 2 O and duration of 2 min per step was performed. Ventilation gain and loss, the global inhomogeneity (GI) index, trend of end-expiratory lung impedance (EELI) and regional compliance (C reg ) for estimation of overdistension and collapse were calculated. Largely diverging results of PEEP selection among the measures were defined as differences ≥ 4 PEEP steps (i.e. ≥ 8 cmH 2 O). In 30 ARDS patients we examined so far, 3 patients showed significant differences in PEEP selections. Overdistension and collapse estimation based on C reg tended to select lower PEEP while the GI index and EELI trend suggested higher PEEP settings. Regional inspiration times were heterogeneous indicating that the assumption of a uniform driving pressure in the calculation of C reg may not be valid. Judging by the predominant ventilation distribution in the most dependent regions, these patients were non-recruitable with the applied recruitment method or pressure levels. The existence of differences in the recommended PEEP among the analyzed EIT measures might be an indicator of non-recruitable lungs and heterogeneous airway resistances. In these extreme cases, the largely diverging results may prompt the attending clinician to develop individual ventilation strategies. Clinical Trial Registration Registration number NCT03112512, https ://clini caltr ials.gov/ Registered 13 April 2017.

The global inhomogeneity index assessed by electrical impedance tomography overestimates PEEP requirement in patients with ARDS

“…Maybe the GI helps identify responders and non-responders to alveolar recruitment. We hypothesise that in patients who do not respond to alveolar recruitment, GI does not change, while in responders, the GI improves due to alveolar recruitment, inducing changes in ventilation distribution [31][32][33]. The GI is highly correlated with lung recruitability.…”

Influence of overdistension/recruitment induced by high positive end-expiratory pressure on ventilation–perfusion matching assessed by electrical impedance tomography with saline bolus

“…Both studies calculated collapse and overdistension according to the regional compliance curves along PEEP changes. In order to deliver a reliable result, an incremental or decremental PEEP trial with a number of PEEP steps is required [24]. In the current study, we defined recruitment and overdistension based on the ventilation gain and loss, similar to the analysis method introduced previously [25].…”

Electrical impedance tomography in the adult intensive care unit: clinical applications and future directions

“…These two methods were compared and found overall to not significantly differ in PEEP achieved, but with notable discrepancies in 3 patients [22 ▪▪ ], highlighting the need for further research.…”