COMPARISON OF BIOIMPEDANCE AND DOPPLER ULTRASOUND CARDIAC-OUTPUT IN CAPD PATIENTS

The reproducibility and reliability of cardiac output (CO) measurement by transthoracic electrical bioimpedance (TEB) and dual beam Doppler ultrasound methods were compared in 9 uremic patients during treatment with continuous ambulatory peritoneal dialysis (CAPD). CO was measure d simultaneously by each method during supine rest and 70 degrees pass ive head-up tilt on two separate days. The effect on CO after the infu sion of dialysate was also studied on day 1. CO, stroke volume (SV) an d heart rate (HR) measurements were reproducible by each method. The m edian day to day differences (95% confidence intervals) in CO and SV w ere 0.6 (-03, 1.8) l/min and 10 (-1.5 24.5) ml for TEB and 0.7 (-0.5, 2.2) l/min and 13 (-1.0 30.5) ml for Doppler at supine rest; 0.4 (-0.2 , 0.9) l/min and 11 (-0.5, 19.0) ml for TEB and 0.5 (-0.3, 1.2) l/min and 8 (-5.0, 16.0) ml for Doppler during tilt (p > 0.05 in each case). Data were unobtainable by TEB at five time points while none were los t by Doppler. This is due to incorrect HR or poor quality signals dete cted by TEB. CO and SV measured by Doppler were higher than that by TE B during supine rest (p less than or equal to 0.01) but not during pas sive tilt. As a result, there was significant change (p less than or e qual to 0.01) in CO and SV from supine to tilt measured by Doppler but not by TEB. Neither TEB nor Doppler detected significant change (p > 0.05) in CO or SV after the infusion of dialysate, in either the supin e or tilt positions. Although TEB is a more reproducible method than D oppler, it is less reliable in data acquisition and in detecting CO ch ange from the supine to tilt position in CAPD patients. TEB is thus no t a suitable method for CO measurement in these patients under such ci rcumstances. Further studies are required to evaluate the accuracy and limitations of Doppler in these patients.