Electrical Impedance Tomography-based Ventilation Patterns in Patients After Major Surgery

General anesthesia and mechanical ventilation have negative impacts on the respiratory system, causing heterogeneous distribution of lung aeration, but little is known about the ventilation patterns of postoperative patients and their association with clinical outcomes.To clarify the phenotypes of ventilation patterns along a gravitational direction after surgery by utilizing electrical impedance tomography (EIT) and to evaluate their association with postoperative pulmonary complications (PPCs) and other relevant clinical outcomes.Adult postoperative patients at high risk for PPCs, receiving mechanical ventilation on ICU admission (N=128) were prospectively enrolled between November 18, 2021 and July 18, 2022. PPCs were prospectively scored until hospital discharge and their association with phenotypes of ventilation patterns was studied. The secondary outcomes were the times to wean from mechanical ventilation and oxygen use and the length of ICU stay.Three phenotypes of ventilation patterns were revealed by EIT: phenotype1 [32%(N=41), a predominance of ventral ventilation], phenotype2 [41%(N=52), homogeneous ventilation], and phenotype3 [27%(N=35), a predominance of dorsal ventilation]. The median PPC score was higher in phenotype1 and phenotype3 than in phenotype2. The median time to wean from mechanical ventilation was longer in phenotype1 vs. phenotype2. The median duration of ICU stay was longer in phenotype1 vs. phenotype2. The median time to wean from oxygen use was longer in phenotype and phenotype3 than in phenotype2.Inhomogeneous ventilation patterns revealed by EIT on ICU admission were associated with PPCs, delayed weaning from mechanical ventilation and oxygen use, and a longer ICU stay.