Using the statistical process control (SPC) method as a quality review tool to analysis the typical value ranges (TVR) of urodynamic measurements based on a single center data.

This single center retrospective study was conducted at the department of urology at our Hospital in October 2022. We selected all the 120 UDS traces in October, but only 84 urodynamic traces met all the inclusion and exclusion criteria  for final analysis.

There were 84 urodynamic traces which met the inclusion and exclusion criteria enrolled for further analysis. 20 females and 64 males with the average age of 58.02±16.09 years. 32 cases were diagnosed with neurogenic bladder dysfunction and 52 cases were diagnosed with non-neurogenic bladder dysfunction. The average initial intravesical pressure was 34.81±10.78 cmH2O, initial abdominal pressure was 30.92±11.14 cmH2O, initial detrusor pressure was 4.20±3.73 cmH2O, then we used scatter diagram to visualize these data for further analysis. Then use these data to make a scatter diagram, and make a standard TVR mark line in each diagram (standard TVR for initial intravesical pressure was 35.4±10.7cmH2O, standard TVR for initial abdominal pressure was 33.1±10.9cmH2O, and standard TVR for initial detrusor pressure was2.3±3.5cmH2O) (Figure 1). The CL was 22.48, UCL was 32.04, LCL was 12.92 for Xbar-control chart, and the CL was 15.78, UCL was 22.57, LCL was 8.9 for s-control chart. Then we used these data to draw the Xbar-control graph and s-control chart separately (Figure 2). According to the defining of the abnormal fluctuation, we could saw 3 abnormal fluctuation in these control chart, which indicated this process may are out of control. We could find that there were 2 cases exceeded the UCL in Xbar-control chart, and 1 case exceeded the UCL in s-control chart. Other cases were all under control.

In our study, we compared our individual initial pressure with the standard TVR: initial intravesical pressure (34.81±10.78 cmH2O vs 35.4±10.7cmH2O), initial abdominal pressure (30.92±11.14cmH2O vs 33.1±10.9cmH2O), initial detrusor pressure (4.20±3.73cmH2O vs 2.3±3.5cmH2O). We further used the visual processing method to convert the data into the image form, and drew the high and low limits of quality control on the image according to the TVR，but we need to point out that this kind of chart is different from the SPC control chart we mentioned later, and the high and low limits mentioned here are also different from UCL and LCL in SPC chart.  There seems no significant difference between the 3 different initial pressures we obtained when compared with their standard TVR, but we could see some fluctuations exceeded the high limits in the scatter diagram, indicating there are some abnormal causes we mentioned before happened, and we should do further analysis for these issues.

In order to further analysis the quality of the beginning of the UDS, we use the Xbar-s control chart to show the data. We drawn the Xbar-control chart and s-control chart separately, and we could find that there were 2 cases exceeded the UCL in Xbar-control chart, and 1 case exceeded the UCL in s-control chart. However, the distribution of data points within the control limits was more uniform. Which means in the begging of the UDS there may be some issues happened may affect the quality of the process, but the overall quality performance is acceptable.  Combining with the scatter diagram we made before, we may can explain this situation. In the scatter diagram we can see some outliers over control line, and these outliers may cause the abnormal fluctuation in the SPC chart.

The clinical value of SPC in the quality review of UDS in numerical data has been confirmed in the previous studies. This study preliminarily verified the using of SPC in measurement value data, such as the TVR of UDS parameters, and we also confirmed the critical value of the TVR in UDS quality control.