measurement of cardiac output ( co ) requires use of invasive or minimally invasive devices ; the use of noninvasive and minimally invasive devices has gained popularity in recent years . the bioreactance technique is a relatively new , continuous , totally non - invasive technique for measuring co that is easily implemented . this new technique involves analyzing phase shifts of a delivered oscillating current that occur when the current traverses the thoracic cavity , and differs from traditional bioimpedance techniques that rely on analysis of changes in signal amplitude . most validation studies in critically ill patients have shown good correlation and/or agreement of bioreactance values compared with co values obtained using other devices in patients admitted after cardiac surgery [ 2 - 4 ] . however , validation in critically ill patients is lacking . as part of the internal evaluation of a bioreactance device before its implementation in the unit ( evaluation of new non - invasive monitoring systems before introduction in the unit does not require the approval of the ethics committee in our institution ) , we compared co values obtained using the bioreactance technique ( nicom system ; cheetah medical inc . , portland , or , usa ) with those measured using semi - continuous cardiac output by thermodilution ( cco ) with a pulmonary artery catheter ( vigilance , edwards lifesciences , irvine , ca , usa ) . in 11 patients the co values were compared at study inclusion and each time a relevant change in hemodynamics and/or in therapeutics ( for example , fluid challenge , inotrope or vasopressor infusions ) was observed ( table 1 ) . patient characteristics data in parentheses represent maximal dose , range ( g / minute for norepinephrine and g / kg.min for dobutamine ) . we recorded bioreactance co ( average of five values over a 5-minute period ) just after obtaining the pulmonary artery catheter cco ( average of five cco values over a 5-minute period ) . we collected 141 pairs of measurements ( 3 to 23 per patient ) ; the duration of monitoring was at least 3 hours but never exceeded 24 hours . there was poor correlation between the two techniques ( correlation coefficient r = 0.145 ) ( figure 1 ) . to limit the time effect , we randomly selected one pair of measurements for each patient - but this did not improve the results ( r = 0.13 ) . bland and altman analysis with correction for multiple measurements showed wide limits of agreement ( figure 2 ) . the time course of co was not well tracked either , sometimes with opposite trends between the two devices . correlation between pulmonary artery catheter semi - continuous cardiac output by thermodilution and bioreactance cardiac output . pulmonary artery catheter semi - continuous cardiac output by thermodilution and bioreactance cardiac output : bias and agreement . co , cardiac output ; pac - cco , pulmonary artery catheter semi - continuous cardiac output by thermodilution . the bioreactance technique is dependent on diffusion of electrical current , so interstitial edema may interfere with measurements ; we believe this is the most probable explanation for the poor correlation . whatever the reason , these data suggest that caution should be applied when using bioreactance devices in critically ill patients .
measurement of cardiac output ( co ) using minimally invasive devices has gained popularity . in 11 patients we compared co values 
 obtained using the bioreactance technique - a new continuous , totally non - invasive co monitor - with those obtained by semi - continuous thermodilution using a pulmonary artery catheter . 
 we obtained co measurements at study inclusion and after any relevant change in hemodynamic status ( spontaneous or during fluid challenge , inotrope or vasopressor infusions ) . 
 there was a poor correlation between the two techniques ( r = 0.145 ) . 
 these data suggest that caution should be applied when using bioreactance devices in critically ill patients .