Lower FiO2 during general anesthesia can reduce lung atelectasis. The objectives are to evaluate the effect of two FiO2 (0.4 and 1) during low PEEP ventilation over lung perfusion distribution, volume, and regional ventilation. These variables were evaluated at two PEEP levels and unilateral lung atelectasis.


In this exploratory study, ten healthy female piglets (32.3±3.4kg) underwent mechanical ventilation in two atelectasis models: 1) Bilateral gravitational atelectasis (N=6), induced by changes in PEEP and FiO2 in three combinations: high PEEP with low FiO2 (FiO2=0.4), zero PEEP (PEEP0) with low FiO2 (FiO2=0.4), and PEEP0 with high FiO2 (FiO2=1); 2) Unilateral atelectasis (N=6) was induced by left bronchial occlusion, with the left lung aerated (FiO2=0.21) and low aerated (FiO2=1) (N=5 for this step). Measurements were conducted after 10 minutes in each step, encompassing assessment of respiratory mechanics, oxygenation, hemodynamics; lung ventilation and perfusion by electrical impedance tomography (EIT); lung aeration and perfusion by computed tomography (CT).


During bilateral gravitational atelectasis, PEEP reduction increased atelectasis in dorsal regions, decreased respiratory compliance, and distributed lung ventilation to ventral regions with a parallel shift of perfusion to the same areas. With PEEP0, there were no differences between low and high FiO2 in respiratory compliance (23.9±6.5ml/cmH2O vs. 21.9±5.0, P=0.441), regional ventilation, and regional perfusion, despite higher lung collapse (18.6±7.6% vs. 32.7±14.5, P=0.045) with high FiO2. During unilateral lung atelectasis, the deaerated lung had a lower shunt (19.3±3.6% vs. 25.3±5.5, P=0.045) and lower CT perfusion to the left lung (8.8±1.8% vs. 23.8±7.1, P=0.007).


PEEP0 with low FiO2, compared with high FiO2, did not produce significant changes in respiratory system compliance, regional lung ventilation, and perfusion despite significantly lower lung collapse. After left bronchial occlusion, the shrinkage of the parenchyma with FIO2=1 enhanced HPV, reducing intrapulmonary shunt and perfusion of the nonventilated areas.