To analyze the quality control in urodynamic study by using proportion control chart of statistical process control.

15 urodynamic study (UDS) traces conducted at the Urodynamic center of our hospital were randomly selected from each month of 2020, with a total of 180 samples been included according to the including criteria. Statistical process control (SPC), a tool provided visualization to the problem of process management [1], was applied to analyze the incidence of all artifacts, which including non-standard zero setting, did not do the cough test, did not record all the UDS measurements, catheter displacement, and baseline drift. According to the study data and Shewart chart selecting criteria, we chose the proportion control chart (p-chart) with 3 standard deviations (3-sigma) control limits for further analysis. We calculated the Center line (CL), Lower Control Limit (LCL), which equal to CL-3-sigma, Upper Control Limit (UCL), which equal to CL+3-sigma, of all artifacts incidence in UDS process. Then we did the stabilization process to get controlled quality control in UDS process.

We calculated the proportion of the incidence of all kinds of artifacts in each month, through p-chart calculation formula, we got the value of CL, UCL, and LCL in one year (Table 1). We set the value of LCL to zero when LCL had a negative value, since the proportion cannot be negative. The Zone A, B, C were divided in the p-chart according to 3-sigma limit rule. The Zone A is between the 2-sigma and the 3-sigma limit, the zone B is between the 2-sigma and 1-sigma limit, and the zone C is between the 1-sigma and the center line [2]. (Figure 1. a).

Our results showed that 8 data points were within the zone C, 11 data points were within the zone B, but an outlier was found in October (0.87) in the p-chart for all artifacts, which exceeded the UCL (0.69). This might be a result of special cause variation. After the value in October was removed, the p-chart showed a significant improvement in quality control as evidenced by all data points were within the zone A (Figure 1. b).

By using the p-chart, we found the total artifacts occurrence showed an outlier point above the UCL in October, which might indicate an abnormal quality control in October. Then we did further investigation, we found that in October 2020, our urodynamic center had accepted some candidates from other hospitals, for these candidates, they might have a lack of practical experience and knowledge of UDS. This indicated that attending recognized training would increase the ability to perform urodynamic examination [3]. SPC approach plays an important role in the evaluation of UDS process and guides us to find the cause of the bad behavior in process management, and it could be served as a predictive model to predict the future performance of UDS process. Any point outside of the control limits indicates something unusual (a special cause). A point below the LCL represents an opportunity to see if something positive happened to the process. However, further analysis with larger sample is still needed.

Keller DS, Reif de Paula T, Yu G, Zhang H, Al-Mazrou A, Kiran RP. Statistical Process Control (SPC) to drive improvement in length of stay after colorectal surgery. Am J Surg. 2020 Jun;219(6):1006-1011. doi: 10.1016/j.amjsurg.2019.08.029. Epub 2019 Sep 10. PMID: 31537326.
Pereira P, Seghatchian J, Caldeira B, Xavier S, de Sousa G. Statistical methods to the control of the production of blood components: principles and control charts for variables. Transfus Apher Sci. 2018 Feb;57(1):132-142. doi: 10.1016/j.transci.2018.02.022. Epub 2018 Feb 20. PMID: 29526479.
Shamout S, Andonian S, Kabbara H, Corcos J, Campeau L. Teaching and evaluation of basic urodynamic skills in urology residency programs: Randomized controlled study. Neurourol Urodyn. 2018 Nov;37(8):2724-2731. doi: 10.1002/nau.23728.

Continence 2S2 (2022) 100255
DOI: 10.1016/j.cont.2022.100255