Máttar J A
Brazilian Group for Bioimpedance Study, São Paulo, Brazil.
New Horiz. 1996 Nov;4(4):493-503.
In the past several years, considerable interest has developed in the study of total body bioimpedance analysis (TBBIA) and body composition in healthy subjects. This simple and noninvasive technique uses derived and regression equations to validate data comparative to the gold standards of total body water determination and body composition. However, this approach has not proved to be of value in the critically ill patient with distorted body composition under the effects of multiple drugs and interventions. Notwithstanding, in recent years several authors have demonstrated the usefulness of this technique, apart from derived equations, relying solely in the judicious interpretation of the primary impedance parameters: resistance (R, ohms [omega], reactance (Xc, omega) and the derived phase angle (phi, degrees). The principles of bioelectrical impedance postulate that R is the opposition of total body water and electrolytes to the flow of an alternating current of low amplitude and high frequency, typically 800 microA and 50 kHz, and Xc is the capacitance produced by tissue interface and cell membranes. The phase shift is quantified geometrically as the angular transformation of the ratio Xc/R and is designated as phi. Altered cellular membrane function is a common feature of the septic patient and it has been systematically associated with a significant low Xc and phi. On the other hand, the fluid balance can be precisely monitored by the changes in R, and the serial measurements of the relation Xc/R (or the phi) has been utilized to discriminate between normal subjects and patients, and between septic and nonseptic critically ill patient. Some authors have demonstrated that this relation Xc/R is highly correlated with mortality and could be used for the staging of critically ill patients throughout their stay in the ICU. The role of TBBIA as a simple and noninvasive technique, and its implications for the management of critically ill patients are presented and discussed. Areas for future investigations, with single and multiple frequency, have the potential to clarify many aspects of this emergent technology at the bedside.
在过去几年中，对健康受试者的全身生物电阻抗分析（TBBIA）和身体成分研究产生了浓厚兴趣。这种简单且无创的技术使用推导方程和回归方程来验证与全身水测定和身体成分金标准相比的数据。然而，在受多种药物和干预影响、身体成分已改变的重症患者中，这种方法尚未证明有价值。尽管如此，近年来一些作者已证明，除了推导方程外，仅依靠对主要阻抗参数（电阻（R，欧姆[Ω]）、电抗（Xc，Ω）和推导的相位角（φ，度））的明智解释，该技术是有用的。生物电阻抗原理假定，R是全身水和电解质对低幅度、高频交流电（通常为800微安和50千赫）流动的阻力，而Xc是组织界面和细胞膜产生的电容。相位偏移通过Xc/R比值的角度变换进行几何量化，称为φ。细胞膜功能改变是脓毒症患者的常见特征，并且一直系统性地与显著降低的Xc和φ相关。另一方面，通过R的变化可精确监测液体平衡，并且Xc/R（或φ）关系的系列测量已用于区分正常受试者与患者，以及脓毒症和非脓毒症重症患者。一些作者已证明，这种Xc/R关系与死亡率高度相关，可用于重症患者在重症监护病房（ICU）住院期间的分期。本文介绍并讨论了TBBIA作为一种简单无创技术的作用及其对重症患者管理的影响。单频和多频未来研究领域有可能在床边阐明这项新兴技术的许多方面。
