[Thoracic impedance in the determination of hydration following heart surgery under extracorporeal circulation].

Changes in thoracic water content are measurable by determining basic impedance (Zo). In 57 cardiac surgical patients Zo decreased postoperatively by an average 24% corresponding to water retention of about 1.51. On the second postoperative day the difference to the initial preoperative value was still 8.5% corresponding to a water amount of over 500 ml. A close mathematic correlation exists between changes in the basic impedance (delta Zo) and fluid balance with a correlation coefficient of 0.94. The simple, non-invasive method is suitable for therapeutic control of fluid balance and quantitative diagnosis of pulmonary hyperhydration forms of various causes.