Effects of inhaled nitric oxide on ventilation/perfusion mismatch assessed by electrical impedance tomography in patients with ARDS: a prospective observational study

Our study aimed to assess the effects of inhaled nitric oxide (iNO) on ventilation/perfusion mismatch, and individual variability in patients with acute respiratory distress syndrome (ARDS) by electrical impedance tomography (EIT). This single-center, prospective physiological study enrolled mechanically ventilated ARDS patients. All patients initially received 5 ppm iNO; responders (≥ 20% increase in PaO2/FiO2 at 30 min) maintained this dose, while non-responders had their dose doubled every 30 min, up to 40 ppm, until achieving a ≥ 20% improvement. The trial lasted 3 h. EIT data and clinical respiratory and hemodynamic parameters were collected at baseline (0 h), and at 30 min and 3 h after iNO initiation. At 30 min, 36.7% (11/30) of patients responded, associated with younger age and lower prevalence of hypertension. Among responders, the proportion of ventral perfusion significantly increased at 3 h, with this change already observed at 30 min. Responders also showed a significant reduction in the proportion of only perfused units in the dorsal region at 30 min; at the whole-lung level, the proportions of only perfused units and unmatched units decreased. In contrast, non-responders showed an increased proportion of only perfused units in both the dorsal region and whole lung at 3 h compared to baseline, following prolonged high-dose iNO administration. The response to iNO varied. In responders, EIT showed a potential redistribution of lung perfusion toward ventral regions, with reductions in the proportions of only perfused units and unmatched units in the whole lung.