Woltjer H H, Bogaard H J, van der Spoel H I, de Vries P M
Academic Hospital VU, Department of Pulmonary Medicine, Amsterdam, The Netherlands.
Intensive Care Med. 1996 Aug;22(8):766-71. doi: 10.1007/BF01709519.
Obesity is thought to be one of the conditions in which the impedance cardiographic method is less reliable for estimating stroke volume (SV). This led to the introduction of a weight correction factor, sigma, into the equation according to Sramek and Bernstein. However, no scientific evidence has been published to support the use of this factor. The objectives of the present study are to evaluate the influence of body weight on the accuracy of impedance cardiography and to validate Bernstein's weight correction factor by comparison with thermodilution in patients after coronary bypass surgery.
Prospective clinical study.
A surgical intensive care unit in a university hospital.
37 consecutive patients 24-36 h after coronary bypass surgery, sub-divided into a normal-weight group (n = 24), patients whose weight deviated less than 15% from their ideal weight, and an obese group (n = 13), patients whose weight deviated more than 15% from their ideal weight.
Kubicek's impedance cardiographic method and Sramek and Bernstein's method to assess SV are applied and compared to thermodilution. In order to study the validity of sigma, the results are compared between 24 patients with normal weight and 13 obese patients.
A significant correlation between miscalculation of SV by impedance cardiography and the degree of obesity for Sramek and Bernstein's method is found when sigma is not included in the equation (r = -0.55, p < 0.05). This relation, however, remained significant when sigma was included in the equation (r = -0.40, p < 0.05). Kubicek's method shows no significant correlation for this relation (r = -0.30). Besides this, Sramek and Bernstein's method underestimates SV significantly in the obese group, independent of the use of sigma in the equation. These results are explained as being intrinsic to the equation, according to Sramek and Bernstein. In the whole group the impedance-derived SV did not significantly differ from SV as measured by means of thermodilution, independent of the method used to calculate SV. However, a considerably better correlation and agreement (mean difference +/- 2 standard deviations is found when Kubicek's method is applied (r = 0.90, 0.5 +/- 17.1 ml vs 0.64, -4.9 +/- 31.8 ml for Sramek and Bernstein's method).
Weight significantly influences Sramek and Bernstein's method of impedance cardiography, whereas Kubicek's method is not biased by this factor.
肥胖被认为是阻抗心动描记法在估计每搏输出量（SV）时可靠性较低的情况之一。根据斯拉梅克和伯恩斯坦的研究，这导致在公式中引入了一个体重校正因子σ。然而，尚未有科学证据支持使用该因子。本研究的目的是评估体重对阻抗心动描记术准确性的影响，并通过与冠状动脉搭桥术后患者的热稀释法进行比较，验证伯恩斯坦的体重校正因子。
前瞻性临床研究。
一所大学医院的外科重症监护病房。
37例冠状动脉搭桥术后24 - 36小时的连续患者，分为正常体重组（n = 24），即体重与理想体重偏差小于15%的患者，以及肥胖组（n = 13），即体重与理想体重偏差超过15%的患者。
应用库比切克的阻抗心动描记法以及斯拉梅克和伯恩斯坦的方法来评估每搏输出量，并与热稀释法进行比较。为了研究σ的有效性，对24例正常体重患者和13例肥胖患者的结果进行比较。
当公式中不包括σ时，发现阻抗心动描记法对每搏输出量的误算与斯拉梅克和伯恩斯坦方法的肥胖程度之间存在显著相关性（r = -0.55，p < 0.05）。然而，当公式中包括σ时，这种关系仍然显著（r = -0.40，p < 0.05）。库比切克的方法在这种关系中未显示出显著相关性（r = -0.30）。除此之外，无论公式中是否使用σ，斯拉梅克和伯恩斯坦的方法在肥胖组中均显著低估了每搏输出量。根据斯拉梅克和伯恩斯坦的研究，这些结果被解释为公式本身所固有的。在整个组中，无论使用何种方法计算每搏输出量，阻抗衍生的每搏输出量与通过热稀释法测量的每搏输出量均无显著差异。然而，当应用库比切克的方法时，发现相关性和一致性明显更好（平均差异±2标准差，库比切克方法为r = 0.90，0.5±17.1 ml；斯拉梅克和伯恩斯坦方法为0.64，-4.9±31.8 ml）。
体重显著影响斯拉梅克和伯恩斯坦的阻抗心动描记法，而库比切克的方法不受该因素影响。
