Noninvasive continuous cardiac output monitoring in perioperative and intensive care medicine

Abstract

The determination of blood flow, i.e. cardiac output, is an integral part of haemodynamic monitoring. This is a review on noninvasive continuous cardiac output monitoring in perioperative and intensive care medicine. We present the underlying principles and validation data of the following technologies: thoracic electrical bioimpedance, thoracic bioreactance, vascular unloading technique, pulse wave transit time, and radial artery applanation tonometry. According to clinical studies, these technologies are capable of providing cardiac output readings noninvasively and continuously. They, therefore, might prove to be innovative tools for the assessment of advanced haemodynamic variables at the bedside. However, for most technologies there are conflicting data regarding the measurement performance in comparison with reference methods for cardiac output assessment. In addition, each of the reviewed technology has its own limitations regarding applicability in the clinical setting. In validation studies comparing cardiac output measurements using these noninvasive technologies in comparison with a criterion standard method, it is crucial to correctly apply statistical methods for the assessment of a technology's accuracy, precision, and trending capability. Uniform definitions for 'clinically acceptable agreement' between innovative noninvasive cardiac output monitoring systems and criterion standard methods are currently missing. Further research must aim to further develop the different technologies for noninvasive continuous cardiac output determination with regard to signal recording, signal processing, and clinical applicability.

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“…The Wigner-Ville distribution (WVD) is the basic QTFD and is defined by taking the Fourier transform (FT) of an instantaneous auto-correlation function K z (t,τ) described in Eq. (1). (1) where K z (t, τ) is defined as (2) and where z(t) is the analytic associate of a real signal x(t) obtained with the Hilbert transform z(t) = x(t) + jH{x(t)}.…”

“…In the last years, impedance cardiography (ICG) has proven to be an advantageous, inexpensive, non-invasive technique for monitoring the cardiovascular hemodynamic state of patients undergoing several medical procedures [1,2,3,4,5,6,7]. This work investigates the frequency content of the ICG signals in different moments of an anesthesia procedure: previous to the induction of anesthesia and after the start of an anesthesia procedure in the surgery room.…”

Cardiac output monitoring: less invasiveness, less accuracy?

“…Although intermittent pulmonary artery thermodilution using a pulmonary artery catheter is still supposed to be the clinical gold standard for the assessment of CO [4], lessinvasive and even non-invasive technologies have been developed in growing numbers in recent years and proposed for CO monitoring-including single-indicator transpulmonary thermodilution and calibrated or uncalibrated pulse contour analysis [3,5].…”

“…In addition, the proprietary pulse contour analysis algorithms consider biometric patient data or properties of the arterial pressure waveform to derive CO; in certain patients or clinical situations these mathematical assumptions might not hold true [19]. Various limitations regarding technical problems and mathematical algorithms have also been described for all completely noninvasive technologies for CO assessment [5].…”

How to “validate” newly developed cardiac output monitoring devices

“…Nevertheless, whilst calculating the precision of the reference method is not very feasible in CO agreement studies, we suggest that all future studies follow the ''guide'' set by Hapfelmeier and co-workers and comply with their recommendations. As such, at least unity between studies can be increased which allows a more sound meta-comparison of all CO method agreement studies and the ongoing discussion [10][11][12] on whether or not new CO monitoring devices can or should be implemented clinically, can be funded on more sound and appropriate statistical analyses.…”