Objective. The aim of the present study was to evaluate the variation of tidal volume-to-impedance ratio (V_T/Z_T) during positive end-expiratory pressure (PEEP) titration with electrical impedance tomography (EIT) measurement.Approach. Forty-two patients with acute respiratory distress syndrome were retrospectively analyzed. An incremental and subsequently a decremental PEEP trial were performed with steps of 2 cm H₂O and duration of 2 min per step during volume-controlled ventilation with decelerating flow. EIT measurement was conducted in the 5th intercostal space andV_Twas recorded simultaneously. The variation ofV_T/Z_T(RatioV) was defined as the changes in percentage to average ratio per cm H₂O PEEP change. A z-score > 1 was considered as a significant variation and an implication that the measurement plane was inadequate.Main results. TheRatioVof 42 patients was 1.29 ± 0.80%·cm H₂O^-1. A z-score of 1 corresponded to the variation of 2.09%·cm H₂O^-1. Seven patients (16.7%) had a z-score > 1 and showed either positive or negative correlation between the volume-to-impedance ratio and PEEP.Significance. Electrode placement at 5th intercostal space might not be ideal for every individual during EIT measurement. Evaluation of volume-to-impedance ratio variation is necessary for patients undergoing maneuvers with wide alteration in absolute lung volume.

Tsai-Fen Chen

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