Hypothesis / aims of study
The Bladder Outlet Obstruction Index (BOOI) Nomogram categorizes men into three groups: obstructed (BOOI > 40), unobstructed (BOOI < 20), and equivocal (BOOI 20-40) [1]. Many men with a combination of voiding and storage lower urinary tract symptoms (LUTS) who undergo urodynamics with pressure-flow studies (PFS) often fall into this equivocal "grey area," making it challenging to determine whether surgical intervention would be beneficial.
The study aims to evaluate whether replacing detrusor pressure at maximum flow (Pdet-Qmax) with maximum detrusor pressure (Pdet-max) in the BOOI formula reduces the occurrence of equivocal micturition rates and to analyze its clinical implications.
Study design, materials and methods
The data of men undergoing urodynamic testing with pressure-flow studies in 2022 were analyzed (based on an estimated incidence of 25% of equivocal BOOI results and aiming to detect a relative 20% subjective improvement after surgical intervention, with a 5% alpha level and 80% power, the calculated sample size was 75 patients).
Men who underwent radical prostatectomy were excluded from the study. Clinical parameters obtained included age, medical history and chronic medications such as alpha-blockers, anti-muscarinics, and beta-3 agonists, along with previous trans-urethral prostatectomy (TURP), indwelling catheter use and predominant storage symptoms. Urodynamic studies were analyzed, and data on uroflowmetry (including volume, Qmax, and post-void residual), filling cystometry (occurrence of detrusor overactivity, bladder compliance, and maximum cystometric capacity), and pressure-flow studies (including voided volume, Qmax, Pdet-Qmax, and Pdet-max) were observed.
The BOOI index was calculated twice for each patient, first using the “regular” formula (Pdet-Qmax - 2 × Qmax) and then with the "modified" formula (Pdet-max - 2 × Qmax). Additionally, data concerning surgical outcomes in patients who eventually underwent TURP were also analyzed. Subjective improvement after surgery was evaluated during follow-up appointments by the treating urologist.
Results
Eighty-one patients were included in the final analysis, with a mean age of 63 (±13) years. Among them, 55 patients (73%) presented with predominant storage symptoms, while 9 patients (12%) had an indwelling urinary catheter. Alpha-blockers were prescribed to 42 patients (56%) and anti-muscarinics/beta-3 agonists were prescribed to 25 patients (33%). Additionally, 9 patients (12%) had undergone TURP previously.
During the filling cystometry, 34 patients (42%) exhibited unstable detrusor activity, while 26 patients (32%) demonstrated abnormal bladder compliance.
The mean values of Pdet-Qmax and Pdet-max were 39 ± 19 cm H2O and 54 ± 34 cm H2O, respectively.
Utilizing the BOOI "regular" formula, 15 patients (18%) were classified as obstructed, 33 (41%) as unobstructed, and the remaining 33 patients (41%) fell into the equivocal category. By substituting Pdet-Qmax with Pdet-max in the BOOI formula, an additional 11 patients initially categorized as equivocal using the "regular" formula were reclassified as obstructed (33%). Upon follow-up, 4 out of these 11 patients (37%) eventually underwent TURP, resulting in subjective improvement in 2 patients post-surgery (50%).
TURP was performed in 8 patients with BOOI > 40 using the “regular” formula, with subjective improvement in 7 patients (87%).
Interpretation of results
Previous studies have indicated that patients with obstructed BOOI tend to experience greater benefits from TURP surgery compared to those with equivocal voiding [2]. This study aimed to evaluate whether substituting Pdet-Qmax with Pdet-max in the BOOI formula would lead to a reduction in equivocal micturition observed during pressure-flow studies (PFS). Additionally, it aimed to investigate the potential benefits of prostate surgery, if any, in the subgroup of patients who were reclassified to obstructed due to this modification.
When substituting these parameters in the BOOI formula, 33% of patients were re-categorized as obstructed. Among these "newly obstructed" patients, 37% underwent TURP, with 50% reporting subjective improvement in micturition. When analyzing all patients classified as obstructed (using either Pdet-Qmax or Pdet-max in the BOOI formula) and comparing their surgical outcomes to patients classified as obstructed solely when Pdet-Qmax was used in the formula, additional 28% experienced subjective improvement in micturition.
Despite the study's limited total number of surgeries and the mixed indications for performing urodynamics, a substantial reduction in equivocal rates, along with added surgical benefits, is observed in patients reclassified as obstructed using Pdet-max in the BOOI formula. Its supplementary application may facilitate decision-making for patients with equivocal voiding and inconclusive interpretation of PFS curves. Nonetheless, further prospective studies are essential to definitively validate these findings.