Influence of systemic vascular resistance on cardiac output measured by new non-invasive cardiac output monitor

Introduction

Early manipulation of hemodynamic variables has been reported to be able to improve the outcome of patients. Cardiac output (CO) was an important parameter to understand the status of hemodynamics. Recently, the pulse-contour method is widely used to estimate CO, because it is non-invasive and easy to use. However, the change in the systemic vascular resistance (SVR) affects CO measured by the pulse-contour method. In this study, we evaluated the new non-invasive cardiac output monitor [1] based on pulse pressure analysis combined with pulse-wave transition time (estimated continuous CO; esCCO) compared with the conventional thermodilution method under a clinical setting.

Methods

Twenty-five surgical patients who underwent cardiac or vascular surgery (ASA physical status 2) were enrolled in this study. After anesthesia induction, radial arterial catheter and pulmonary artery catheter were inserted. Intermittent cardiac output (ICO) was measured by thermodilution method in triplicate and averaged (<5°C saline 10 ml in each measurement) using Vigilance (Edwards Life Science, Irvine, CA, USA). Echocardiogram, pulse oximetry and arterial blood pressure were also monitored and connected to personal computer to calculate esCCO. Bland and Altman plots were used to evaluate the percentage difference in CO in relation to SVR.

Results

One hundred matched sets of data were obtained. The limit of agreement (bias ± 2SD of bias) was -2.9 ± 31.9%. Only five measurements were exceeded - 30% against ICO. Each SVR was 1,159, 1,376, 1,418, 2,567, 3,150 dyn·s/m⁵.

Conclusions

The difference in most CO was within ±30% against the reference values, although CO was underestimated by esCCO under the relative high SVR. COs estimated by esCCO were acceptable under the clinical setting. Therefore, we concluded that esCCO was a useful algorithm to estimate CO.