Department of Intensive Care, B4, Leiden University Medical Center, P.O.B. 9600, 2300 RC Leiden, The Netherlands.
Anesth Analg. 2012 Apr;114(4):803-10. doi: 10.1213/ANE.0b013e318247fa44. Epub 2012 Feb 17.
Mean systemic filling pressure (Pmsf) can be determined at the bedside by measuring central venous pressure (Pcv) and cardiac output (CO) during inspiratory hold maneuvers. Critical closing pressure (Pcc) can be determined using the same method measuring arterial pressure (Pa) and CO. If Pcc > Pmsf, there is then a vascular waterfall. In this study, we assessed the existence of a waterfall and its implications for the calculation of vascular resistances by determining Pmsf and Pcc at the bedside.
In 10 mechanically ventilated postcardiac surgery patients, inspiratory hold maneuvers were performed, transiently increasing Pcv and decreasing Pa and CO to 4 different steady-state levels. For each patient, values of Pcv and CO were plotted in a venous return curve to determine Pmsf. Similarly, Pcc was determined with a ventricular output curve plotted for Pa and CO. Measurements were performed in each patient before and after volume expansion with 0.5 L colloid, and vascular resistances were calculated.
For every patient, the relationship between the 4 measurements of Pcv and CO and of Pa and CO was linear. Baseline Pmsf was 18.7 ± 4.0 mm Hg (mean ± SD) and differed significantly from Pcc 45.5 ± 11.1 mm Hg (P < 0.0001). The difference of Pcc and Pmsf was 26.8 ± 10.7 mm Hg, indicating the presence of a systemic vascular waterfall. Volume expansion increased Pmsf (26.3 ± 3.2 mm Hg), Pcc (51.5 ± 9.0 mm Hg), and CO (5.5 ± 1.8 to 6.8 ± 1.8 L · min(-1)). Arterial (upstream of Pcc) and venous (downstream of Pmsf) vascular resistance were 8.27 ± 4.45 and 2.75 ± 1.23 mm Hg · min · L(-1); the sum of both (11.01 mm Hg · min · L(-1)) was significantly different from total systemic vascular resistance (16.56 ± 8.57 mm Hg · min · L(-1); P = 0.005). Arterial resistance was related to total resistance.
Vascular pressure gradients in cardiac surgery patients suggest the presence of a vascular waterfall phenomenon, which is not affected by CO. Thus, measures of total systemic vascular resistance may become irrelevant in assessing systemic vasomotor tone.
通过在吸气保持操作期间测量中心静脉压（Pcv）和心输出量（CO），可以在床边确定平均系统充盈压（Pmsf）。可以使用相同的方法测量动脉压（Pa）和 CO 来确定临界关闭压（Pcc）。如果 Pcc > Pmsf，则存在血管瀑布。在这项研究中，我们通过在床边确定 Pmsf 和 Pcc 来评估瀑布的存在及其对血管阻力计算的影响。
在 10 例接受心脏手术后机械通气的患者中，进行吸气保持操作，短暂地将 Pcv 增加并将 Pa 和 CO 降低至 4 个不同的稳态水平。对于每个患者，将 Pcv 和 CO 的值绘制在静脉回流曲线上以确定 Pmsf。同样，通过绘制 Pa 和 CO 的心室输出曲线来确定 Pcc。在每个患者中，在容量扩张 0.5 L 胶体前后进行测量，并计算血管阻力。
对于每个患者，Pcv 和 CO 的 4 次测量以及 Pa 和 CO 的关系都是线性的。基础 Pmsf 为 18.7 ± 4.0 mmHg（平均值 ± 标准差），与 Pcc 45.5 ± 11.1 mmHg 有显著差异（P < 0.0001）。Pcc 和 Pmsf 的差值为 26.8 ± 10.7 mmHg，表明存在系统性血管瀑布。容量扩张增加了 Pmsf（26.3 ± 3.2 mmHg）、Pcc（51.5 ± 9.0 mmHg）和 CO（5.5 ± 1.8 至 6.8 ± 1.8 L·min^-1）。动脉（Pcc 上游）和静脉（Pmsf 下游）血管阻力分别为 8.27 ± 4.45 和 2.75 ± 1.23 mmHg·min·L^-1；两者之和（11.01 mmHg·min·L^-1）与总系统性血管阻力（16.56 ± 8.57 mmHg·min·L^-1）显著不同（P = 0.005）。动脉阻力与总阻力相关。
心脏手术患者的血管压力梯度表明存在血管瀑布现象，而 CO 对其无影响。因此，评估全身血管舒缩性时，总全身血管阻力的测量可能变得无关紧要。
