Abstract:

Objective  To study the different positive end-expiratory pressure (PEEP) on pulmonary shunt fraction and oxygenation during one-lung ventilation (OLV), and to explore the best PEEP value in OLV.Methods  Thirtypatients with ASA Ⅰ-Ⅱ level elective thoracotomy with OLV were selected.The blood gas analysis were performed
 in the lateral position at ventilation 30 min (T1), OLV 30 min (T2), 5 cmH₂O OLV PEEP 30 min (T3), and 10 cm

H₂O OLV PEEP 30 min (T4).At each time point, the PaO₂, PaCO₂, SaO₂, pH, HR, mean arterial pressure (MAP), and peak airway pressure (Ppeak) were recorded, and the intrapulmonary shunt(Qs / Qt) was calculated.Results Compared with two-lung ventilation, the PaO₂ was decreased and the Qs / Qt was increased significantly (P<0.05), the PaO₂ was increased from (200.20 ± 145.25) mmHg to (299.55±138.83) mmHg (P<0.05) and the Qs / Qt was decreased (P<0.05) at the duration of T2 to T3; the PaO₂ was decreased from (299.55 ± 138.83) mmHg to（237.30 ± 135.57） mmHg(P<0.05) and the Qs / Qt was increased (P<0.05) at the duration of T3 to T4; the Ppeak value was increased from T2(21.15±3.60) cmH2O to T4(27.20±3.78) cm

H₂O (P<0.05)  in OLV.Conclusion During OLV, 5 cmH2O PEEP applied in ventilated lung can increase the

PaO₂, decrease the Qs / Qt and prevent the occurrence of hypoxemia.It is more appropriate PEEP value.

Key words: positive end-expiratory pressure, one-lung ventilation, arterial partial pressure of oxygen, pulmonary shunt fraction