Personalized Positive End-Expiratory Pressure in Acute Respiratory Distress Syndrome: Comparison Between Optimal Distribution of Regional Ventilation and Positive Transpulmonary Pressure.

Objectives: Different techniques exist to select personalized positive end-expiratory pressure in patients affected by the acute respiratory distress syndrome. The positive end-expiratory transpulmonary pressure strategy aims to counteract dorsal lung collapse, whereas electrical impedance tomography could guide positive end-expiratory pressure selection based on optimal homogeneity of ventilation distribution. We compared the physiologic effects of positive end-expiratory pressure guided by electrical impedance tomography versus transpulmonary pressure in patients affected by acute respiratory distress syndrome. Design: Cross-over prospective physiologic study. Setting: Two academic ICUs. Patients: Twenty ICU patients affected by acute respiratory distress syndrome undergoing mechanical ventilation. Intervention: Patients monitored by an esophageal catheter and a 32-electrode electrical impedance tomography monitor underwent two positive end-expiratory pressure titration trials by randomized cross-over design to find the level of positive end-expiratory pressure associated with: 1) positive end-expiratory transpulmonary pressure (PEEPPL) and 2) proportion of poorly or nonventilated lung units (Silent Spaces) less than or equal to 15% (PEEPEIT). Each positive end-expiratory pressure level was maintained for 20 minutes, and afterward, lung mechanics, gas exchange, and electrical impedance tomography data were collected. Measurements and Main Results: PEEP(EIT)and PEEP(PL)differed in all patients, and there was no correlation between the levels identified by the two methods (R-s= 0.25;p= 0.29). PEEP(EIT)determined a more homogeneous distribution of ventilation with a lower percentage of dependent Silent Spaces (p= 0.02), whereas PEEP(PL)was characterized by lower airway-but not transpulmonary-driving pressure (p= 0.04). PEEP(EIT)was significantly higher than PEEP(PL)in subjects with extrapulmonary acute respiratory distress syndrome (p= 0.006), whereas the opposite was true for pulmonary acute respiratory distress syndrome (p= 0.03). Conclusions: Personalized positive end-expiratory pressure levels selected by electrical impedance tomography- and transpulmonary pressure-based methods are not correlated at the individual patient level. PEEP(PL)is associated with lower dynamic stress, whereas PEEP(EIT)may help to optimize lung recruitment and homogeneity of ventilation. The underlying etiology of acute respiratory distress syndrome could deeply influence results from each method.