Vaporization and coagulation potentials of new electrovaporization devices for transurethral prostatectomy

Recently, transurethral electrovaporization (EVAP) has been introduced as an alternative for transurethral electroresection as treatment for benign prostatic hyperplasia. This new method combines the use of high electrical power with special developed `EVAP-elements´. Four different EVAP-elements were applied to bovine myocardial tissue with constant speed (1-4 mm/s) while constant force (20 gm) was applied. Two different electrosurgical generators, the F40 and F300 (both Valleylab) were used. The output power of the F40 decreases rapidly when the tissue impedance, between EVAP-element and return electrode, increases. The F300 has a built-in impedance feedback loop to remain the output power constant in the high impedance region. When above threshold power all the different EVAP-elements vaporize on average 0.8 ml tissue per track of 5 cm length. Coagulation around the track extended 1-2 mm into the tissue, sufficient for hemostasis. The threshold power for the F300 was lower than with the F40, 175 and 250 W respectively, and depended on translation speed and EVAP-element