Comparison of Niccomo™ bioimpedance cardiac output with lithium dilution (LIDCO™) in ICU patients

Introduction

Knowledge of cardiac output (CO) and vascular resistance has been shown to influence and direct clinical decisions in critical care patients [1, 2]. The choice of which technology to measure CO, however, remains troublesome and confusing. The accuracy and invasiveness of CO measurement technologies are variable, as are the concepts surrounding whether calibration is necessary. These issues of invasiveness and accuracy are central to decisions relating to CO monitor selection and are perceived to have an inverse relationship. Niccomo™ is a new impedance cardiography (ICG) algorithm that is noninvasive ('plug and play') and uses no calibration. LiDCO™ is a well validated indicator dilution (ID) technique. This study compared the accuracy of the new ICG algorithm versus the LiDCO™ standard.

Methods

With consent/assent, 14 critically ill patients were studied. The ICG monitor was set up and, following two initial ID determinations, CO measurements were recorded from both monitors simultaneously at one to six time points over 6 hours.

Results

Fifty-one paired measurements were obtained from the ICG and ID monitors. The mean (± SD) COs were 6.11 (1.62) l/min and 4.67 (1.25) l/min, respectively. The mean bias was -1.44 l/min with a precision (standard deviation) of ± 2.02 l/min. The lower and upper limits of agreement were -5.48 l/min (mean - 2 SD) and 2.61 l/min (mean + 2 SD) (P < 0.001). Spearman's correlation analysis showed r = 0.149, P = 0.297. On direct comparison of the initial paired readings, the Niccomo™ estimated a lower CO than the LiDCO™; however, the differences were extremely variable.

Conclusion

ICG showed both poor agreement and poor correlation versus ID. The percentage error (53%) lies outside the graphically derived accepted 30% level [3], and in this patient population suggests that this ICG algorithm does not have the required accuracy to drive, or the clinical confidence to make, haemodynamic management decisions.