Decreases in Electric Thoracic Impedance During transurethral Resection of the Prostate: an Index of Early Water Intoxication

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Abstract
Thoracic impedance of 18 patients undergoing transurethral resection of the prostate was measured 15 min preoperatively, and 30 and 60 min after the start of the operation. Impedance variations were compared to variation in cardiac output, serum Na osmolality and alveolar-arterial O2 tension difference. Thoracic impedance, initially 24.6 .+-. 0.3, decreased to 23.8 .+-. 0.5, 30 min after the onset of the operation (P < 0.0005) and 22.9 .+-. 0.5, 30 min later (P < 0.01 from previous reading and 0.0005 from control). Patients in whom impedance had decreased 10% or more from control values received 10 mg furosemide i.v. 60 min after the onset of the operation. This therapy permitted the restoration of impedance values, cardiac output, alveolar-arterial oxygen tension difference and serum Na osmolality to values statistically similar to those found in the 10 patients who had not sustained such precipitous decreases in impedance within 60 min. Apparently, the measurement of thoracic impedance during transurethral prostatic surgery offers the most sensitive index of early water intoxication. Measurements can be obtained without delay in the operating room and, thus, permit immediate correction of the condition.