Positive end-expiratory pressure applied to the dependent lung during one-lung ventilation improves oxygenation and respiratory mechanics in patients with high FEV1

Background and objective: The aim of this study was to test the efficacy of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation, taking into consideration underlying lung function in order to select responders to PEEP. Methods: Forty-six patients undergoing open-chest thoracic surgical procedures were studied in an operating room of a university hospital. Patients were randomized to receive zero end-expiratory pressure (ZEEP) or 10 cmH₂O of PEEP to the dependent lung during one-lung ventilation in lateral decubitus. The patients were stratified according to preoperative forced expiratory volume in 1 s (FEV₁) as an indicator of lung function (below or above 72%). Oxygenation was measured in the supine position, in the lateral decubitus with an open chest, and after 20 min of ZEEP or PEEP. The respiratory system pressure-volume curve of the dependent hemithorax was measured in supine and open-chest lateral decubitus positions with a super-syringe. Results: Application of 10 cmH₂O of PEEP resulted in a significant increase in PaO₂ (P <0.05). This did not occur in ZEEP group, considered as a time matched control. PEEP improved oxygenation only in patients with high FEV₁ (from 11.6 ± 4.8 to 15.3 ± 7.1 kPa, P <0.05). There was no significant change in the low FEV₁ group. Dependent hemithorax compliance decreased in lateral decubitus, more in patients with high FEV₁ (P <0.05). PEEP improved compliance to a greater extent in patients with high FEV₁ (from 33.6 ± 3.6 to 48.4 ± 3.9 mL cmH₂O_-1, P <0.05). Conclusions: During one-lung ventilation in lateral decubitus, PEEP applied to the dependent lung significantly improves oxygenation and respiratory mechanics in patients with rather normal lungs as assessed by high FEV₁.