Measurement of surgical diathermy current during trans-urethral resection of the prostate gland.

A system is described that has been developed to measure the surgical diathermy current passing through the patient during each cut of a trans-urethral resection of the prostate gland (TURP), with 1.5% glycine solution as irrigant. The immediate aim was to distinguish capsular tissue of the male prostate gland from the hyperplastic adenomatous tissue within it. The ultimate aim was to prevent resection into the surgical capsule which can easily result in excessive blood loss and absorption of irrigant. The system was used in a conventional theatre setting with a commercial diathermy system (Eschmann TD 411-S) of known output characteristics. Measurements were made in 12 patients during resection with a standard loop, involving typically 75 cuts in each patient (60 in adenoma and 15 in capsule). In 8 of these patients this was followed by roller ball placement on typically 10 sites each of capsule or residual adenoma at very low diathermy settings. The results showed great variability both between patients, and between different cuts in the same patient, with no consistent difference between tissues identified under direct vision as adenoma and surgical capsule. Physical reasons are suggested for the observed variability, and it is concluded that it is not possible to use this technique to guide tissue resection in the prostate.