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(b) for a simultaneous electrical online estimation of changes in blood hematocrit Delta H [%] and temperatures Delta T [K] in cardiopulmonary bypass (CPB). Z(b) of fixed blood volumes at varying H and T were measured by an impedance analyzer and changes in blood conductivity sigma(b) and relative permittivity epsilon(b) computed. Correlation analysis were based on changes in sigma(b) with H or T at f = 1 MHz while H and T equations were developed by correlating changes in epsilon(b) with H and T at dual frequencies of f = 1 MHz and f = 10 MHz which best capture blood plasma Z(p) and red blood cell cytoplasm Z(cyt) impedances respectively. Results show high correlations between sigma(b) and H (R-2 = 0.987) or sigma(b) and T (R-2 = 0.9959) indicating dependence of the electrical parameters of blood on its H and T. Based on computed epsilon(b), changes in blood hematocrit Delta H and temperature Delta T at a given time t are estimated as Delta H(t) = 1.7298 Delta epsilon(b) (f = 1 MHz) - 1.0669 Delta epsilon(b) (f = 10 MHz) and Delta T(t) = -2.186 Delta epsilon(b) (f = 1 MHz) + 2.13 Delta epsilon(b) (f = 10 MHz). When applied to a CPB during a canine mitral valve plasty, Delta H and Delta T had correlations of R-2 = 0.9992 and R-2 = 0.966 against H and T respectively as measured by conventional devices.