Multi-frequency bioimpedance measurements of children in intensive care.

Bioimpedance spectroscopy is used to monitor the condition of the tissues of children staying in intensive care for the treatment of meningitis. The results are significant, with the angular frequency at maximum reactance lying between 1500 and 6400 x 10(3) rads(-1), whereas in a control group, this value does not exceed 900 x 10(3) rads(-1). The ratio between the specific conductance at zero and that at infinite frequency (this ratio is proportional to total body volume/volume of extracellular space) remains constant at 1.4 and equal to the ratio in the control group, despite infusions with physiological saline. The electrical parameters are associated with physiological ones and indicate that the membrane 'capacitance' decreases, as a result of the illness, from approximately 0.4 in the control group to 0.05 in the patient group. However, there is a time-delay between the onset of illness and the change in membrane capacitance. It is also found that the ratio between extracellular and intracellular specific conductivity in the group of patients and controls remains constant at approximately 4.3. The changes in the physiological and electrical parameters were compared with chemical parameters that were measured during the stay in intensive care.