USE OF NONINVASIVE BIOELECTRIC IMPEDANCE TO PREDICT CARDIAC-OUTPUT INOPEN-HEART RECOVERY

Cardiac outputs (CO) measured by bioelectric impedance (Z) and thermod ilution (TD) were compared in ten stable, non-ventilated male coronary artery bypass patients (mean age 59 +/- 12 years) in an open heart re covery unit. The measurements were obtained blindly in three sequentia l body positions (supine, 45-degrees, final supine) using either a cal culated value for resistivity (p) (based upon hematocrit with blood sa mpled at the time of the study) to estimate CO(Z), or assumed values o f p = 135.5 OMEGA cm and p = 150 OMEGA cm. The results indicate high c orrelations between the two measurement methods (range: r = 0.97 to 0. 99) in the initial supine position for all resistivity conditions foll owed by a progressive decline when body position was changed to 45-deg rees and supine (range: r = 0.74 to 0.90). The highest overall correla tions and closest absolute mean cardiac output values were obtained wh en p was calculated from actual hematocrit values obtained at the time of the study. Applying a two-way ANOVA to assess the simultaneous eff ects of method (TD vx. Z) and position change (supine, 45-degrees, sup ine), no significant main effects or interactions were found when card iac output values were estimated using the calculated measurement of p . However, significant main effects of method were found when p was as sumed to be either 135.5 OMEGA cm (p greater-than-or-equal-to 0.005) o r 150.0 OMEGA cm (p greater-than-or-equal-to 0.0001), with impedance s howing a tendency to overestimate cardiac output. In conclusion, our f indings suggest that impedance is a valid method to estimate cardiac o utput in this subpopulation of patients in open heart recovery provide d that p is calculated at the time the study is performed.