Noninvasive cardiac output monitoring: a clinical validation

Introduction

Our objective was to evaluate the clinical utility of noninvasive cardiac output monitoring (NICOM), a new tool for automatic continuous cardiac output (CO) monitoring based on chest bioreactance, using continuous thermodilution as reference (PAC-CCO).

Method

We included 110 consecutive adult patients immediately after cardiac surgery in a prospective, single-center study taking place in the ICU. CO measurements obtained from NICOM and PAC-CCO were simultaneously recorded minute by minute (Figure 1). We evaluated the accuracy, precision, responsiveness, and reliability of NICOM for detecting CO changes. Tolerance for each of these parameters was specified prospectively.

Figure 1

Mixed venous hemoglobin oxygen saturation (SvO₂) vs cardiac output (CO) by noninvasive cardiac output monitoring and Swan on Mister197.

Results

A total of 65,888 pairs of CO measurements were collected. Mean reference values for PAC-CCO ranged from 2.79 to 9.27 l/min. During periods of stable PAC-CCO (slope < ± 10%, 2SD/mean <20%), the correlation between NICOM and PAC-CCO was R = 0.82; bias was +0.16 ± 0.52 l/min (+4.0 ± 11.3%), and the relative error was 9.1 ± 7.8%. In 85% of patients the relative error was <20%. During periods of increasing CO, slopes were similar with the two methods in 96% of patients and intraclass correlation was positive in 96%. Corresponding values during periods of decreasing CO were 90% and 84%, respectively. Precision was always better with NICOM than with PAC-CCO. During hemodynamic challenges, changes were 3.1 ± 3.8 minutes faster with NICOM (P < 0.01) and amplitude of changes were not different (not significant). Finally, sensitivity of the NICOM for detecting significant directional changes was 93% and specificity was 93%.

Conclusion

CO measured by NICOM had most often acceptable accuracy, precision, and responsiveness in a wide range of circulatory situations.