Efficacy of one lung protective ventilation regimen based on quarsi-static pressure-volume curve in patients undergoing thoracic surgery

Objective To evaluate the efficacy of PEEP set according to pressure-volume (P-V) curve for one lung ventilation (OLV) in patients undergoing thoracic surgery.Methods One hundred and twenty ASA Ⅱ or Ⅲ patients of both sexes aged 20-60 yr weighing 40-80 kg undergoing lobectomy under general anesthesia were enrolled in this study.Double lumen tube was inserted.Correct positioning was verified by fiberoptic bronchoscopy.The patients were mechanically ventilated.P-V curve was determined at 3 min of two-lung ventilation (TLV).Lower inflection point (LIP) was measured and the pressure at LIP (PLIP) was recorded.The patients were randomly divided into 5 groups (n ＝ 24 each):control group (group C) and 4 lung protective ventilation regimen groups ( groups P1-4 ).PEEP was set at 0 and VT was set at 10 ml/kg in group C.PEEP was set at 0 and VT was set at 6 ml/kg in group P1.PEEP was set at PLIP- 2 cm H2O and VT was set at 6 ml/kg in group P2.PEEP was set at PLIP and VT was set at 6 ml/kg in group P3.PEEP was set at PLIP + 2 cm H2O and VT was set at 6 ml/kg in group P4.Peak airway pressure (Ppeak),plateau airway pressure (Pplat),airway resistance (Raw) and lung compliance (CL ) were measured and recorded during OLV and TLV after a period of stabilization.Arterial blood samples were taken before induction of anesthesia and at 20 min of TLV and 20 min of OLV for blood gas analysis.Qs/Qt was calculated.Arterial blood samples were collected at the beginning and end of OLV for determination of plasma concentrations of IL-6 and TNF-α(by ELISA).Results Compared with group C,Ppeak and Pplat were significantly increased while Raw was decreased and plasma IL-6 concentration was significantly decreased at the end of OLV in group P4.PaCO2 was significantly higher during TLV and OLV in groups P1-4 than in group C.There was no significant difference in the parameters of respiratory mechanics,blood gases and plasma IL-6 and TNF-α concentrations among groups P1,2.3.Compared with groups P1,2,3,Ppeak and Pplat were significantly increased while plasma IL-6 concentration was decreased at the end of OLV in group P4.Conclusion Mechanical ventilation with VT set at 6ml/kg and PEEP at PLIP + 2 cm H2 O provides best venfilatory efficacy for OLV in terms of oxygenation and inhibition of inflammatory response. Key words: Positive-pressure respiration; Tidal volume