Extravascular absorption of irrigating fluid during TURP. The role of transmural bladder pressure as the driving pressure gradient.

The critical intravesical pressure range for extravascular absorption of irrigating fluid (EVA) during transurethral resection of the prostate (TURP) is determined by the pressure in the perivesical tissue. This means that the transmural bladder pressure (detrusor pressure), calculated by deducting perivesical pressure from intravesical pressure during cystometry, is the pressure gradient behind EVA. The transmural pressure in 6 patients undergoing TURP has been studied both before and during epidural anaesthesia, using both conventional medium-fast fill cystometry and "free-flow" cystometry through the resectoscope. Epidural block does not influence the transmural pressure response on filling the bladder and neither does the type of infusion. A positive transmural pressure, and thereby a pressure gradient for EVA, exists already during the very early phase of bladder filling. Incomplete perforation of the prostatic capsule and clotting, as well as the accumulation of irrigating fluid in the perivesical tissue, probably moderate the rate of absorption.