Monitoring of peripheral edema using electrical bioimpedance measurements

A peripheral edema monitor, based on the measurement of bioimpedance from electrodes located on the forearm is described. The monitor is essentially an 8-channel electrical impedance tomograph; it applies a sinusoidal current (1-4 mA @ 20-100 kHz) to adjacent electrodes and measures voltage gradients from the other pairs of electrodes. A reference data set is acquired before surgery, and subsequent sets are used for computing changes in the conductivity of the subcutaneous layer, the region whose electrical properties are most likely to be affected by peripheral edema. Simulations with a finite-element model of an elliptical cross-section cylinder, representing the forearm, suggest that conductivity changes of 5% can be detected. The relationship between conductivity changes and parameters characterizing the evolution of peripheral edema in critically-ill patients remains to be established