Transpulmonary pressures and EIT-derived alveolar collapse and overdistension in ARDS: association and comparison of two PEEP titration strategies

Determining the optimal positive end-expiratory pressure (PEEP) to maximize alveolar recruitment while minimizing overdistension remains a clinical challenge. This study investigated the relationship between transpulmonary pressures and electrical impedance tomography (EIT)-derived estimates of alveolar collapse and overdistension, and compared the PEEP levels and physiological conditions produced by two titration strategies, in patients with moderate-to-severe acute respiratory distress syndrome (ARDS). We conducted a physiological study involving 38 mechanically ventilated ARDS patients. Each patient underwent a decremental PEEP trial (20 to 4 cmH₂O), with continuous EIT monitoring and esophageal pressure measurements to calculate end-expiratory (P L, e ) and end-inspiratory (P L, i ) transpulmonary pressures. Percentages of alveolar collapse and overdistension were derived from EIT data. Their associations with transpulmonary pressures were assessed using repeated-measures correlation and linear mixed-effects models. The discriminative performance of P L, e and P L, i for EIT-derived collapse or overdistension exceeding 10% of the lung was assessed. We also compared PEEP levels determined by EIT-guided (best compromise between overdistension and collapse) versus esophageal pressure-guided (lowest PEEP yielding a positive P L, e ) strategies. P L, e was inversely associated with EIT-derived collapse and P L, i positively associated with EIT-derived overdistension (rrm = − 0.85 and 0.89; all p < 0.001). In mixed-effects models, each 1 cmH₂O decrease in P L, e corresponded to a 3.0% increase in collapse, and each 1 cmH₂O increase in P L, i to a 1.9% increase in overdistension. P L, e and P L, i discriminated collapse and overdistension exceeding 10% with AUCs of 0.84 and 0.80. Within the applied PEEP range, a P L, e <0.2 cmH₂O was associated with collapse > 10%, while P L, i >23.3 cmH₂O was associated with overdistension > 10%, both with ≥ 90% specificity. PEEP levels determined using EIT were significantly higher than those based on esophageal pressure (12.0 [8.0–14.0] vs. 8.0 [4.8–11.3] cmH 2 O; p < 0.001), resulting in reduced alveolar collapse, indicating more effective alveolar recruitment, and improved ventilation in the dependent lung region. However, the EIT-guided strategy also led to a slight increase in overdistension and reduced compliance in the non-dependent lung. Transpulmonary pressure measurements are strongly associated with EIT-derived estimates of alveolar collapse and overdistension in ARDS patients. However, EIT- and esophageal pressure-guided strategies result in different PEEP settings, respiratory mechanics, and patterns of alveolar collapse and overdistension.