Use of noninvasive bioelectric impedance to predict cardiac output in open heart recovery.
Cardiac outputs (CO) measured by bioelectric impedance (Z) and thermodilution (TD) were compared in ten stable, non-ventilated male coronary artery bypass patients (mean age 59 +/- 12 years) in an open heart recovery unit. The measurements were obtained blindly in three sequential body positions (supine, 45 degrees, final supine) using either a calculated value for resistivity (p) (based upon hematocrit with blood sampled at the time of the study) to estimate CO(Z), or assumed values of p = 135.5 omega cm and p = 150 omega cm. The results indicate high correlations between the two measurement methods (range: r = 0.97 to 0.99) in the initial supine position for all resistivity conditions followed by a progressive decline when body position was changed to 45 degrees and supine (range: r = 0.74 to 0.90). The highest overall correlations and closest absolute mean cardiac output values were obtained when p was calculated from actual hematocrit values obtained at the time of the study. Applying a two-way ANOVA to assess the simultaneous effects of method (TD vx. Z) and position change (supine, 45 degrees, supine), no significant main effects or interactions were found when cardiac output values were estimated using the calculated measurement of p. However, significant main effects of method were found when p was assumed to be either 135.5 omega cm (p > or = 0.005) or 150.0 omega cm (p > or = 0.0001), with impedance showing a tendency to overestimate cardiac output. In conclusion, our findings suggest that impedance is a valid method to estimate cardiac output in this subpopulation of patients in open heart recovery provided that p is calculated at the time the study is performed.
Demeter
R J
RJ
Department of Medical Research, Methodist Hospital of Indiana, Indianapolis 46206.
Parr
K L
KL
Toth
P D
PD
Woods
J R
JR
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001809:Blood Viscosity / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D002307:Cardiography, Impedance; D001026:Coronary Artery Bypass; D003327:Coronary Disease / Q000503:physiopathology / Q000601:surgery*; D006400:Hematocrit; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000503:physiopathology*; D011187:Posture / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology; D013815:Thermodilution