Department of Anaesthesiology & Intensive Care, Aarhus University Hospital, Skejby, 8200 Aarhus N, Denmark.
Ultraschall Med. 2012 Apr;33(2):152-9. doi: 10.1055/s-0031-1281832. Epub 2011 Dec 16.
Respiratory changes in the diameter of the inferior vena cava (IVC) have been validated as a measure of volume status and preload responsiveness during spontaneous breathing and mechanical ventilation. However, many intensive care patients are ventilated with triggered positive pressure ventilation (PPV). In this setting, there is no evidence regarding IVC collapsibility (IVCc) as a surrogate for preload. We aimed to elucidate the effects of increasing levels of triggered PPV and of varying preload conditions on the IVCc.
10 healthy volunteers were connected to a ventilator through a tight-fitting mask and exposed to 6 different levels of positive end-expiratory pressure (PEEP) and pressure support (PS) after a baseline reading. All ventilator settings were performed at neutral preload (horizontal position), low preload (reverse-Trendelenburg) and high preload (Trendelenburg position with an intravenous fluid bolus). At each ventilator setting, the IVC was imaged throughout at least 1 respiratory cycle using 3 commonly used ultrasound techniques including sagittal M-mode and 2-dimensional echocardiography in both sagittal and transverse views.
Increasing PS diminished IVCc (p = 0.01) in the reverse-Trendelenburg position, and increasing PEEP caused a higher IVCc in the Trendelenburg position (p = 0.02). In the horizontal position, no significant effects of increasing PS, PEEP or a combination of the two were seen. Overall ANOVA analysis showed that IVCc was not independent of preload. During PPV, IVCc was highest at neutral preload at most ventilator settings, IVCc was lowest at low preload, while high preload generally facilitated an IVCc between neutral and high preload. In addition, sagittal M-mode and transverse 2-dimensional echocardiography overestimated IVCc as compared to sagittal 2-dimensional echocardiography.
The compiled results of this study show that IVCc cannot be held as a valid measure of preload status during PPV. This may be explained by systematic alterations in other determinants for IVCc. Comparison of methods encourages the use of sagittal 2-dimensional echocardiography for dynamic imaging of the IVC. Sagittal M-mode and transverse 2-dimensional echocardiography overestimate IVCc as compared to sagittal 2-dimensional echocardiography.
下腔静脉（IVC）直径在呼吸时的变化已被验证可作为评估容量状态和对自主呼吸及机械通气时前负荷反应性的指标。然而，许多重症监护患者接受的是触发式正压通气（PPV）。在这种情况下，尚无关于 IVC 可塌陷性（IVCc）作为前负荷替代指标的证据。我们旨在阐明增加触发式 PPV 水平和不同前负荷条件对 IVCc 的影响。
10 名健康志愿者通过紧密贴合的面罩连接到呼吸机，并在基线读数后暴露于 6 种不同水平的呼气末正压（PEEP）和压力支持（PS）。所有通气设置均在中性前负荷（水平位置）、低前负荷（反向特伦德伦伯卧位）和高前负荷（特伦德伦伯卧位并静脉输液）下进行。在每个通气设置下，使用 3 种常用的超声技术，包括矢状 M 模式和矢状及横切二维超声，在至少 1 个呼吸周期内对 IVC 进行成像。
PS 增加会降低反向特伦德伦伯卧位时的 IVCc（p = 0.01），而 PEEP 增加会使特伦德伦伯卧位时的 IVCc 更高（p = 0.02）。在水平位置，PS、PEEP 或两者的增加均未引起明显的影响。总体方差分析显示，IVCc 不受前负荷影响。在 PPV 期间，大多数通气设置下中性前负荷时 IVCc 最高，低前负荷时 IVCc 最低，而高前负荷通常使 IVCc 在中性和高前负荷之间。此外，与矢状二维超声相比，矢状 M 模式和横切二维超声高估了 IVCc。
本研究的综合结果表明，在 PPV 期间，IVCc 不能作为前负荷状态的有效衡量指标。这可能是由于 IVCc 的其他决定因素发生了系统性改变。方法比较鼓励使用矢状二维超声对 IVC 进行动态成像。与矢状二维超声相比，矢状 M 模式和横切二维超声高估了 IVCc。
