The electrical impedance of plasma: a laboratory simulation of the effect of changes in chemistry.

To evaluate the role of plasma chemistry in the genesis of electrical impedance of blood, a laboratory simulation was performed using solutions prepared so as to mimic plasma chemistry abnormalities that are seen in the critically ill. There was a 15% increase of impedance due to decrease in sodium chloride concentration from 140 mmol/L to 120 mmol/L, and a 12% decrease of impedance due to increase in sodium chloride to 160 mmol/L. Impedance changes secondary to other chemistry abnormalities were small and probably not significant, with the exception of a change of albumin concentration from 80 gm/L to 50 gm/L, which induced a 6% increase in impedance. Using this data, a model was constructed to predict changes in whole blood resistivity, and this was extrapolated in two simulations of plasma chemistry abnormalities to predict alterations of calculated impedance stroke volume in excess of 5%.