Arterial pressure-based cardiac output in septic patients: different accuracy of pulse contour and uncalibrated pressure waveform devices

Abstract

IntroductionWe compared the ability of two devices estimating cardiac output from arterial pressure-curve analysis to track the changes in cardiac output measured with transpulmonary thermodilution induced by volume expansion and norepinephrine in sepsis patients.MethodsIn 80 patients with septic circulatory failure, we administered volume expansion (40 patients) or introduced/increased norepinephrine (40 patients). We measured the pulse contour-derived cardiac index (CI) provided by the PiCCO device (CIpc), the arterial pressure waveform-derived CI provided by the Vigileo device (CIpw), and the transpulmonary thermodilution CI (CItd) before and after therapeutic interventions.ResultsThe changes in CIpc accurately tracked the changes in CItd induced by volume expansion (bias, -0.20 ± 0.63 L/min/m2) as well as by norepinephrine (bias, -0.05 ± 0.74 L/min/m2). The changes in CIpc accurately detected an increase in CItd ≥ 15% induced by volume expansion and norepinephrine introduction/increase (area under ROC curves, 0.878 (0.736 to 0.960) and 0.924 (0.795 to 0.983), respectively; P < 0.05 versus 0.500 for both). The changes in CIpw were less reliable for tracking the volume-induced changes in CItd (bias, -0.23 ± 0.95 L/min/m2) and norepinephrine-induced changes in CItd (bias, -0.01 ± 1.75 L/min/m2). The changes in CIpw were unable to detect an increase in CItd ≥ 15% induced by volume expansion and norepinephrine introduction/increase (area under ROC curves, 0.564 (0.398 to 0.720) and 0.541 (0.377 to 0.700, respectively, both not significantly different from versus 0.500).ConclusionsThe CIpc was reliable and accurate for assessing the CI changes induced by volume expansion and norepinephrine. By contrast, the CIpw poorly tracked the trends in CI induced by those therapeutic interventions.

The precision of PiCCO®measurements in hypothermic post‐cardiac arrest patients

“…Bolus transpulmonary thermodilution measurements are required for the estimation of these haemodynamic and pulmonary variables using the PiCCO. Several studies have investigated the accuracy of these values [17,[20][21][22]], but few have described the precision of this technique [23,24]. Accuracy refers to how close a measurement is to the actual or real value, and precision refers to how close repeated measurements are to each other [25].…”

Cardiac output monitoring: less invasiveness, less accuracy?

“…Moreover, changes in vasomotor tone can impair the measurement performance of pulse contour analysis that might however be improved by frequent calibration to CO assessed with a more invasive technology (e.g. transpulmonary thermodilution) [16][17][18][19]. 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].…”

Can the “FloTrac” really track flow in septic patients?

“…The capacity of the uncalibrated FloTrac to estimate CO has been well established in surgical patients but has been seriously questioned by some studies in vasoplegic states [3][4][5][6]. For instance, the FloTrac did not allow tracking of the trends in CO in whom arterial pressure was modified by norepinephrine administration [6].…”

“…For instance, the FloTrac did not allow tracking of the trends in CO in whom arterial pressure was modified by norepinephrine administration [6]. This suggested that the FloTrac estimation of CO was ''disorientated'' by large changes in arterial compliance and vasomotor tone, which might be problematic for septic shock patients and, more generally, for use in the intensive care unit.…”

“…Of note, this tracking ability was not found to be better than with the second FloTrac version. More importantly, the serial data varied little and the study was not designed for testing the ability of the third version to systematically evaluate some planned CO trends, in particular when total systemic vascular resistance changes by a large extent, as can occur when changing the dose of vasopressors [6]. Hence, although this study clearly suggests that the accuracy of the FloTrac device has been improved and that it might be suitable for septic shock patients, it is to speculate that further studies will investigate whether this improved accuracy is resistant to large changes in arterial compliance and vascular tone, continuing the laborious search for the ''gold nugget''……”