Clinical evaluation of the non-invasive cardiac output (NICO) monitor in the intensive care unit.

The Non-invasive Cardiac Output (NICO) monitor (Novametrix Medical Systems Inc., Wallingford, CT, U.S.A.) utilizes a minimally-invasive partial rebreathing method to determine cardiac output by means of a differential form of the Fick equation. We evaluated the NICO monitor by comparing its output to paired measurements obtained by the standard thermodilution (TD) technique in patients who had recently undergone cardiac surgery. Forty-two paired measurements were carried out in 12 patients. The correlation between the two methods was moderate with a correlation coefficient of 0.691. Repeated measures ANOVA showed that TD measures of cardiac output were significantly higher than those obtained by the NICO monitor (P = 0.0003). Comparison of the two techniques using the method described by Bland and Altman showed decreased correlation at higher values of cardiac output. We conclude that the NICO monitor may well have a place in intensive care monitoring, provided patients are not breathing spontaneously and are able to tolerate a 4 mmHg rise in PaCO2. It is less suitable for use in patients with a high cardiac output state.