The International Continence Society (ICS) working groups have published recommendations for standardised quality control measures required to ensure Good Urodynamic Practice (GUP) when performing urodynamic studies for lower urinary tract assessment(1). One such important quality control step is ensuring the physiological accuracy of initial resting pressures being recorded. This is of particular importance for the measurement of detrusor pressure (pdet), which directly influences the assessment of bladder outlet obstruction. Inaccuracies in initial resting pdet may therefore lead to the suggestion of inappropriate and unnecessary surgical treatment if left uncorrected. It has been previously suggested that >60% of urodynamic tests display non-physiological resting pressure readings, requiring both additional catheter flushing and bladder filling before accurate pressure values are obtained(2). However, these results did not enable differentiation between cases for which flushing alone would have been sufficient, from those that also required bladder filling to obtain suitable resting pressures. 

This study aims to evaluate the need for filling as a further quality control measure after flushing, to ensure both accurate pressure transmission and acceptable resting pressure measurements(3).

Data was collected retrospectively from consecutive urodynamic traces performed during September 2020. Urodynamic tests were conducted with water-filled pressure measurement catheters in accordance with ICS Good Urodynamic Practices. Eligible traces were analysed for evidence of a good quality control check (cough ratio response within 70%3) and resting pdet within recommended limits (-5 to +5 cmH2O in all positions3) prior to filling. For traces found to be of poor quality, the number of catheter flushes and/or the filling volume required to achieve acceptable pressure transmission and acceptable pdet pressures was recorded. The difference between initial pdet and pdet following additional quality control measures was compared. The study was covered by ethical permission granted for retrospective, anonymised analysis of our department data.

A total of 100 traces were included in this study, 47 male and 53 female with an average age of 58.8 years. 71% did not require further quality control after catheter connection and initial priming. 29% required additional quality control measures to ensure both pressure transmission and pdet were within acceptable limits. Of these, 16 required flushing alone, 8 required bladder filling alone and 5 required both flushing and filling (see figure 1). Flushing of the vesical line was primarily performed. The mean volume of bladder filling required was 49.2ml (range from 10-139ml). Of the 29 cases requiring further quality control, 14 displayed a pdet pressure reading outside the acceptable limit. Of these, 9 required catheter flushing and 8 required volume filling. The difference between initial pdet and final pdet following additional quality control measures was -5.79 (± 6.41 cmH2O) and -2.21 (± 3.02 cmH2O) respectively. With quality control measures improving the final pdet and also reducing the range of values.

We have tested the need for, and effects of, flushing water-filled lines and initial filling of the bladder as separate quality control measures in urodynamics.  Previously, it was suggested that the majority of tests require both of these actions to be carried out.  Our results, however, suggest that the majority of tests pass initial quality checks if good catheter priming is routinely performed.  In the 29% of cases where further measures were required, 16% passed quality control tests after only additional line flushing.  Thus, only 13% of tests required subsequent bladder filling in order to pass quality control checks.
In line with ICS recommendations, uroflowmetry is performed as the initial test of urodynamics studies. In some cases, it is likely that there is an element of post-void residual volume remaining in the bladder. The additional performance of urethral pressure profilometry prior to filling cystometry may also influence overall bladder volume, either due to the test itself or increased time for physiological urine production. Both incidences would enable good pressure transmission even before bladder filling was commenced.  Thus, a centre that commences filling cystometry on an entirely empty bladder may find more need to fill slightly before passing initial quality control checks.  However, it is significant that the combination of flushing and filling is much less likely to be required than the recently published data would lead us to believe.

Contrary to previously published data, only 13% of urodynamic tests require bladder filling in order to pass quality assurance checks. Good priming and flushing of lines alone leads to good pressure transmission in the majority of urodynamic tests.

Schäfer W, Abrams P, Liao L, Mattiasson A, Pesce F, Spangberg A, Sterling AM, Zinner NR, van Kerrebroeck P; International Continence Society. Good urodynamic practices: uroflowmetry, filling cystometry, and pressure-flow studies. Neurourol Urodyn. 2002;21(3):261-74. doi: 10.1002/nau.10066. PMID: 11948720.
Rosier, PFWM. Good urodynamic practice: Pressure signal quality immediately after catheter insertion for cystometry with a water-filled pressure transducer system and its relevance for the ICS zero procedure. Neurourology and Urodynamics. 2021; 40: 319– 325. https://doi.org/10.1002/nau.24561
Sullivan, J.G., Swithinbank, L. and Abrams, P. (2012), Defining achievable standards in urodynamics—a prospective study of initial resting pressures. Neurourology and Urodynamics., 31: 535-540. https://doi.org/10.1002/nau.21229