Some urologists apply pressure to a full bladder to express its contents as an indirect measure of urinary flow after prostate resection. Intra-operative flow rate (IOFR) could act as a marker for post-operative success following transurethral resection of prostate (TURP) for treatment of urinary retention. Our aims are to determine if intra-operative flow rate (IOFR) could act as a marker for post-operative success following TURP and to assess the feasibility of a novel intra-operative flow rate technique.

Patients with indwelling urinary catheters for recurrent retention due to benign prostatic hyperplasia were included in this single-centre feasibility cohort study. IOFR is measured immediately before and after resection. The bladder is filled to 300ml, on average 50Nm of force is applied to the abdomen, the voided flow is graded on a 0-5 pre-set scale by two assessors. Outcome data collected over 10 weeks included; flow complications (e.g. urinary retention, catheter dependent), flow rates and patient satisfaction based on the International Prostate Symptom Score. Primary outcome is IOFR diagnostic feasibility and accuracy at predicting catheter free results. Secondary outcomes are complication rates, patient satisfaction scores and outpatient direct uroflowometry.

17 patients included. Average score: Pre-procedure intraoperative flow rate (PrIOFR), post-procedure intraoperative flow rate (PIOFR) and change in IOFR were 1.17(95%CI 0.42-1.94), 3.64(95%CI 2.89-4.39) and 2.47(95%CI 1.7-3.24).
The table compares IOFR thresholds and sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for predicting successful first trial removal of catheter (TROC) and catheter free by follow up (CFF). The best cut off threshold is the combined score of PIOFR + change in flow rate.
ROC analysis for successful first TROC calculated AUC of the combined threshold score as 0.88. Similarly, ROC analysis for CFF calculated AUC for combined score as 0.94. 
IOFR took about two minutes to complete before and after resection, predominantly due to bladder filling time. The technique proved to be simple to perform and straightforward to follow with feedback from the operator, assessors, and theatre staff.

A combined score with a threshold ≥ 4 AND ≥2  correctly predicted 92% of those who were catheter free (sensitivity) and 100% of those who were not catheter free (specificity) at follow up and the positive predictive value was 100% and negative predictive value 83%. The IOFR technique is efficient and requires little resource. In day-to-day clinical practice, the this can lead to a change in management in those predicted to do poorly by objectively generating a clinical decision: either doing further resection of the prostate or inserting an SPC at the same sitting (in individuals with multiple co-morbidities, advanced age/frailty, and those who repeated operative management carries significant risk). This simple, reproducible technique may be of value specifically in resource constrained settings challenged by reduced access to pre-operative investigations.

Intra-operative flow rate during TURP is simple, reproducible, fast and requires minimal resources. In TURP it may predict successful outcomes by identifying patients who will be catheter free post-operatively as opposed to those who will be catheter dependent despite the procedure.