Detection of Pleural Effusion by Internal Thoracic Impedance Method

Early detection of pleural effusion (PLE) would improve the treatment. However, preclinical detection of pleural effusion is often not possible.

Radiographic examination, widely used for detecting pleural effusion ,is not suitable for prolonged monitoring of patients at high risk of developing PLE especially ambulatory or at home (1-9).

The currently available methods for monitoring and early detection such as the measurement of pulmonary capillary wedge pressure or measurement by double indicator thermodilution, are not reliable enough and may themselves lead to complications(2-8).

Yu C-M et al.(9) recently reported successful prediction of CPE by a surgically implanted impedance plethysmograph integrated into a pacemaker . The system was shown to be sufficiently sensitive for cardiogenic pulmonary edema preceding. However this method is invasive and not suitable for wide use (9).

Therefore, these methods are seldom employed for the detection of PLE (3-7). Thus, a safe and accurate technique for early detection and monitoring of PlEf would be of great clinical value. The changes in the blood and extravascular fluid content in the lungs in humans and animals can be easily monitored using a noninvasive and totally safe procedure based on impedance plethysmography (5-12-). This method is based on the fact that the impedance of the lungs decreases with the increase in the fluid and free ions content in them (8,13,). However, it proved to be unsuitable for preclinical stage monitoring of PLE (2-8) for several reasons, mainly the low sensitivity of the existing impedance plethysmographs. This is due to the high skin-electrode contact resistance (13,14), which is of an order of magnitude high erthan the impedance of the lung.