Simultaneous electrical online estimation of changes in blood hematocrit and temperature in cardiopulmonary bypass.

Two equations have been developed from multi-frequency measurements of blood impedance Z for a simultaneous electrical online estimation of changes in blood hematocrit ΔH [%] and temperatures ΔT [K] in cardiopulmonary bypass (CPB). Z of fixed blood volumes at varying H and T were measured by an impedance analyzer and changes in blood conductivity σ and relative permittivity ε computed. Correlation analysis were based on changes in σ with H or T at f = 1 MHz while H and T equations were developed by correlating changes in ε with H and T at dual frequencies of f = 1 MHz and f = 10 MHz which best capture blood plasma Z and red blood cell cytoplasm Z impedances respectively. Results show high correlations between σ and H (R = 0.987) or σ and T (R = 0.9959) indicating dependence of the electrical parameters of blood on its H and T. Based on computed ε, changes in blood hematocrit ΔH and temperature ΔT at a given time t are estimated as ΔH(t) = 1.7298Δε (f = 1 MHz) - 1.0669Δε (f = 10 MHz) and ΔT(t) = -2.186Δε (f = 1 MHz) + 2.13Δε (f = 10 MHz). When applied to a CPB during a canine mitral valve plasty, ΔH and ΔT had correlations of R = 0.9992 and R = 0.966 against H and T respectively as measured by conventional devices.