Preoperative Detrusor Contractile Strength Measurement in the BPH Patients with Residual Urine

Kim, Jong Woo; Kim, Ha Young; Yang, Kou Young

Abstract

When the bladder is obstructed by BPH, the contractile strength is increased to empty completely. If the obstruction is too severe to overcome by detrusor contraction, there will be residual urine. If detrusor is still compensated there will be no postoperative residual urine. But if detrusor is decompensated with "fading contraction" there will be postoperative residual urine. So the measuring of detrusor contractile strength is a very important test to predict the postoperative residual urine. We calculated the mechanical power generated per unit area of the detrusor surface(WF; Watts factor) to measure the detrusor contractile strength in 14 BPH patients with more than 100ml of residual urine preoperatively and compared the amount of preoperative residual urine with postoperative residual urine to evaluate the diagnostic value of WF in predicting the absence or presence of residual urine postoperatively. The WF in each 3 patients whose detrusor contractile strength seemed to be decreased with more than 50 ml of postoperative residual urine was less than 4W/m2, that was decreased than normal(4-11W/m2). In contrast, the WF .in each 11 patients whose detrusor contractile strength seemed to be normal or increased with less than 50ml of postoperative residual urine was more than 4W/m2, that was normal or increased. There was no significant difference in the amount of preoperative residual urine between both group of patients(p=0.2253, Wilcoxon rank sum test). There was no statistically significant relationship between the WF and the amount of preoperative residual urine in both group of patients(r =-0.028, p=0.92). In conclusion, WF measurement was a useful test in checking the detrusor contractile strength to predict the absence or presence of postoperative residual urine in patients with more than 100ml of residual urine.