The mechanical stop test and isovolumetric detrusor contractile reserve are associated with immediate spontaneous voiding after transurethral resection of prostate.

Purpose: To identify urodynamic factors associated with the mechanical stop test and immediate spontaneous voiding following transurethral resection of prostate (TURP).
Methods: We identified 90 men who underwent TURP over a 12-month period. Forty-three (mean age 68 years) underwent urodynamic evaluation prior to TURP. Isovolumetric detrusor contractile pressure (P _iso ) was obtained using the mechanical stop test during the voiding phase, and used to calculate detrusor contractile reserve (P _res  = P _iso - P _det @Q _max ). Primary outcome was spontaneous voiding after TURP.
Results: Preoperative catheter-free spontaneous voiding was present in 63% of men (27/43) with a urodynamic (mean ± SD): Q _max 6.2 ± 2.7 mL/s, P _det @Q _max 102 ± 47 cmH ₂ O, P _iso 124 ± 49 cmH ₂ O, P _res 22 ± 16 cmH ₂ O, bladder outlet obstruction index (BOOI) 90 ± 49, and bladder contractility index (BCI) 132 ± 44. The remaining 16 catheter-dependent men demonstrated a urodynamic (mean ± SD): Q _max 3.6 ± 3.3 mL/s, P _det @Q _max 87 ± 38 cmH ₂ O, P _iso 99 ± 51 cmH ₂ O, P _res 10 ± 18 cmH ₂ O, BOOI 82 ± 36, and BCI 106 ± 48. Following TURP, 67% of men voided spontaneously with their first void trial, and in receiver operator analysis of urodynamic measures (P _det @Q _max , P _iso , P _res , BOOI and BCI), only P _res was significantly associated with immediate spontaneous voiding after TURP (threshold P _res  ≥ 9 cmH ₂ O, AUC = 0.681, p = 0.035).
Conclusions: In men who underwent TURP, a P _res  ≥ 9 cmH ₂ O was associated with immediate spontaneous voiding and may be easily incorporated into the postoperative pathway.