[A preliminary study of using the expiratory limb of the pressure-volume curve to estimate the dead space in patients suffering from acute respiratory distress syndrome].

Objective To trace pressure-volume curves (P-V curves) with quasi-static technique in acute respiratory distress syndrome (ARDS) patients,and using it to explain the relationship between the end point of the expiratory limb and the change in the dead space of expiration.Methods A prospective study was conducted.Fourteen ARDS patients receiving mechanical ventilation were included in the study.When P-V curves was traced with quasi-static technique,the spirometer was connected to the flow sensor.The start point of the expiratory limb was defined as tidal volume 1 (Vr1) and the end point as VT2,and the difference between them (ΔVT=VT1-VT2) was calculated.The VT of spirometer (named VT3) and the predetermined VT (VT4) were recorded.Correlations of Δ VT and VT3,as well as VT4 and VT1,were analyzed with correlation analysis.Results Δ VT was (417.40 ± 119.68) ml,and VT3 was (399.29 ± 121.36) ml,Δ VT and VT3 showed a good correlation (r=0.99,P=0.000),demonstrating that the Δ VT of the expiratory limb was correlated with the volume trapped in lung.VT4 was (908.21 ± 106.52) ml,and VT1 was (892.26 ± 106.32) ml,and they showed a good correlation (r=0.99,P=0.000).Conclusion Because of part of the gas trapped at the end of expiration in ARDS patients,the dead space is increased,showing that the expiratory limb of the P-V curve cannot return to the base points,and the Δ VT of the expiratory limb is inversely proportional to the gas volume trapped in lung. Key words: Pressure-volume curve;  Expiratory limb;  Acute respiratory distress syndrome;  Dead space