Editing Cardiac output (section)

=====Statistical analysis of arterial pressure – FloTrac/Vigileo=====

FloTrac/Vigileo ([[Edwards Lifesciences]]) is an uncalibrated, haemodynamic monitor based on pulse contour analysis. It estimates cardiac output (''Q'') using a standard arterial catheter with a manometer located in the femoral or radial artery. The device consists of a high-fidelity pressure transducer, which, when used with a supporting monitor (Vigileo or EV1000 monitor), derives left-sided cardiac output (''Q'') from a sample of arterial pulsations. The device uses an algorithm based on the [[Frank–Starling law of the heart]], which states pulse pressure (PP) is proportional to stroke volume (SV). The algorithm calculates the product of the standard deviation of the arterial pressure (AP) wave over a sampled period of 20 seconds and a vascular tone factor (Khi, or χ) to generate stroke volume. The equation in simplified form is: <math display="inline">SV = \mathrm{std}(AP) \cdot \chi</math>, or, <math display="inline">BP \cdot k \mathrm{\ (constant)}</math>. Khi is designed to reflect arterial resistance; compliance is a multivariate polynomial equation that continuously quantifies arterial compliance and vascular resistance. Khi does this by analyzing the morphological changes of arterial pressure waveforms on a bit-by-bit basis, based on the principle that changes in compliance or resistance affect the shape of the arterial pressure waveform. By analyzing the shape of said waveforms, the effect of vascular tone is assessed, allowing the calculation of SV. ''Q'' is then derived using equation ({{EquationNote|1}}). Only perfused beats that generate an arterial waveform are counted for in HR.{{citation needed|date=October 2014}}

This system estimates Q using an existing arterial catheter with variable accuracy. These arterial monitors do not require intracardiac catheterisation from a pulmonary artery catheter. They require an arterial line and are therefore invasive. As with other arterial waveform systems, the short set-up and data acquisition times are benefits of this technology. Disadvantages include its inability to provide data regarding right-sided heart pressures or mixed venous oxygen saturation.<ref>{{cite journal | vauthors = Singh S, Taylor MA | title = Con: the FloTrac device should not be used to follow cardiac output in cardiac surgical patients | journal = Journal of Cardiothoracic and Vascular Anesthesia | volume = 24 | issue = 4 | pages = 709–11 | date = August 2010 | pmid = 20673749 | doi = 10.1053/j.jvca.2010.04.023 }}</ref><ref>{{cite journal | vauthors = Manecke GR | title = Edwards FloTrac sensor and Vigileo monitor: easy, accurate, reliable cardiac output assessment using the arterial pulse wave | journal = Expert Review of Medical Devices | volume = 2 | issue = 5 | pages = 523–27 | date = September 2005 | pmid = 16293062 | doi = 10.1586/17434440.2.5.523 | s2cid = 31049402 }}</ref> The measurement of Stroke Volume Variation (SVV), which predicts volume responsiveness is intrinsic to all arterial waveform technologies. It is used for managing fluid optimisation in high-risk surgical or critically ill patients. A physiologic optimization program based on haemodynamic principles that incorporates the data pairs SV and SVV has been published.<ref>{{cite journal | vauthors = McGee WT | title = A simple physiologic algorithm for managing hemodynamics using stroke volume and stroke volume variation: physiologic optimization program | journal = Journal of Intensive Care Medicine | volume = 24 | issue = 6 | pages = 352–60 | year = 2009 | pmid = 19736180 | doi = 10.1177/0885066609344908 | s2cid = 12806349 }}</ref>

Arterial monitoring systems are unable to predict changes in vascular tone; they estimate changes in vascular compliance. The measurement of pressure in the artery to calculate the flow in the heart is physiologically irrational and of questionable accuracy,<ref name="Se 2">{{cite journal | vauthors = Su BC, Tsai YF, Chen CY, Yu HP, Yang MW, Lee WC, Lin CC | title = Cardiac output derived from arterial pressure waveform analysis in patients undergoing liver transplantation: validity of a third-generation device | journal = Transplantation Proceedings | volume = 44 | issue = 2 | pages = 424–28 | date = March 2012 | pmid = 22410034 | doi = 10.1016/j.transproceed.2011.12.036 }}</ref> and of unproven benefit.<ref>{{cite journal | vauthors = Takala J, Ruokonen E, Tenhunen JJ, Parviainen I, Jakob SM | title = Early non-invasive cardiac output monitoring in hemodynamically unstable intensive care patients: a multi-center randomized controlled trial | journal = Critical Care | volume = 15 | issue = 3 | pages = R148 | date = June 2011 | pmid = 21676229 | pmc = 3219022 | doi = 10.1186/cc10273 | doi-access = free }}</ref> Arterial pressure monitoring is limited in patients off-ventilation, in atrial fibrillation, in patients on vasopressors, and in those with a dynamic autonomic system such as those with sepsis.<ref name="Bein2" />