Minimally Invasive Monitoring of Cardiac Output in the Cardiac Surgery Intensive Care Unit

Abstract

Cardiac output monitoring in the cardiac surgery patient is standard practice that is traditionally performed using the pulmonary artery catheter. However, over the past 20 years, the value of pulmonary artery catheters has been challenged, with some authors suggesting that its use might be not only unnecessary but also harmful. New minimally invasive devices that measure cardiac output have become available. In this paper, we review their operative principles, limitations, and utility in an integrated approach that could potentially change patients' outcome. However, it is now clear that it is how the monitor is used (ie, the protocol or therapy associated with its use, or its lack thereof), and not the monitor per se, that should be questioned when a patient's outcome is being evaluated.

Comparison of noninvasive cardiac output measurements using the Nexfin monitoring device and the esophageal Doppler

“…However, CO monitoring is challenging from a technological standpoint and several different techniques have been proposed during the last decade [5,6]. Apart from the difficulty in reliably measuring flow, evaluation of new CO monitors still remains controversial [21,[30][31][32][33].…”

“…Several technologies are now available for minimally invasive or noninvasive CO monitoring in the perioperative setting [5,6]. However, most of these are either operator-dependent (esophageal Doppler) or require the use of intra-arterial catheters (pulse contour analysis).…”

What is a fluid challenge?

“…Traditionally, the measurement of SV and CO was possible only with an invasive device such as the pulmonary artery catheter (PAC) [11]. The availability of new less invasive CO monitors has made possible the realtime assessment of SV changes during a fluid challenge in a less invasive fashion [12][13][14].…”

Cardiac Output Assessed by Invasive and Minimally Invasive Techniques

“…Every three minutes, partial rebreathing is initiated by opening the rebreathing valve, which adds 150 mL of dead space to the circuit. The difference between normal and rebreathing ratios are used to calculate pulmonary blood flow [4, 88]. Shunt correction is carried out using Nunn's isoshunt curves, a series of curves that describe the relationship between PaO 2 and FiO 2 for different levels of intrapulmonary shunt.…”