Becher T, Rostalski P, Kott M, Adler A, Schädler D, Weiler N, Frerichs I
Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein, Campus Kiel, Kiel, Germany.
Physiol Meas. 2017 Jun;38(6):1132-1144. doi: 10.1088/1361-6579/aa6923. Epub 2017 Mar 24.
Static or quasi-static pressure-volume (P-V ) curves can be used to determine the lung mechanical properties of patients suffering from acute respiratory distress syndrome (ARDS). According to the traditional interpretation, lung recruitment occurs mainly below the lower point of maximum curvature (LPMC) of the inflation P-V curve. Although some studies have questioned this assumption, setting of positive end-expiratory pressure 2 cmHO above the LPMC was part of a 'lung-protective' ventilation strategy successfully applied in several clinical trials. The aim of our study was to quantify the amount of unrecruited lung at different clinically relevant points of the P-V curve.
P-V curves and electrical impedance tomography (EIT) data from 30 ARDS patients were analysed. We determined the regional opening pressures for every EIT image pixel and fitted the global P-V curves to five sigmoid model equations to determine the LPMC, inflection point (IP) and upper point of maximal curvature (UPMC). Points of maximal curvature and IP were compared between the models by one-way analysis of variance (ANOVA). The percentages of lung pixels remaining closed ('unrecruited lung') at LPMC, IP and UPMC were calculated from the number of lung pixels exhibiting regional opening pressures higher than LPMC, IP and UPMC and were also compared by one-way ANOVA.
As results, we found a high variability of LPMC values among the models, a smaller variability of IP and UPMC values. We found a high percentage of unrecruited lung at LPMC, a small percentage of unrecruited lung at IP and no unrecruited lung at UPMC.
Our results confirm the notion of ongoing lung recruitment at pressure levels above LPMC for all investigated model equations and highlight the importance of a regional assessment of lung recruitment in patients with ARDS.
静态或准静态压力-容积（P-V）曲线可用于确定急性呼吸窘迫综合征（ARDS）患者的肺力学特性。根据传统解释，肺复张主要发生在吸气P-V曲线最大曲率最低点（LPMC）以下。尽管一些研究对这一假设提出了质疑，但在LPMC以上2 cmH₂O设置呼气末正压是一项“肺保护性”通气策略的一部分，该策略已在多项临床试验中成功应用。我们研究的目的是量化P-V曲线不同临床相关点处未复张肺的数量。
分析了30例ARDS患者的P-V曲线和电阻抗断层扫描（EIT）数据。我们确定了每个EIT图像像素的局部开放压力，并将整体P-V曲线拟合到五个S形模型方程，以确定LPMC、拐点（IP）和最大曲率上点（UPMC）。通过单因素方差分析（ANOVA）比较各模型之间的最大曲率点和IP。根据显示局部开放压力高于LPMC、IP和UPMC的肺像素数量，计算LPMC、IP和UPMC处保持闭合的肺像素百分比（“未复张肺”），并同样通过单因素方差分析进行比较。
结果显示，我们发现各模型之间LPMC值的变异性较高，IP和UPMC值变异性较小。我们发现LPMC处未复张肺的百分比很高，IP处未复张肺的百分比很小，UPMC处没有未复张肺。
我们的结果证实了对于所有研究的模型方程，在高于LPMC的压力水平下持续发生肺复张的观点，并强调了对ARDS患者进行肺复张区域评估的重要性。
