Hypothesis / aims of study
The gold standard for pressure monitor in urodynamic studies is a water filled catheter system (WFC). The accuracy of WFC can be affected by air bubbles in the tubing, movement, kinking of tubing, and the position of the external transducer. On the other hand, an air-charged catheter (ACC) system has already gained popularity in some countries because of simplicity and cost effectiveness even though the use of ACC has not been justified by ICS. Some papers suggested cytometry and maximum voiding pressure measurements done with either WFC or ACC will similarly accurate results and are compatible (1,2). However these information for the investigation of pressure flow study using ACC are still limited. Therefore, we investigated to compare the data of pressure flow study using WFC and ACC system and examine the agreement for the gradings of obstruction and detrusor contractility on the basis of BOOI/BCI and Schäfer nomogram.
Study design, materials and methods
From the UDS database between 2017 and 2018, the male patients who underwent consecutive pair of pressure flow study (WFC and ACC systems) were selected for this study. First pressure flow study using WFC were performed. ACC were inserted for consecutive pressure flow study followed by the removal of WCCs. In WFC system a 6 Fr double lumen catheter for Pves and 10Fr balloon catheter for Pabd were utilized and in ACC system 7FD and 7FDR TDOC were utilized. Generally all UDS procedures were performed on the basis of ICS good urodynamics 2016. The pressure flow study date using WFC and ACC systems were compared. The grading of BOO and detrusor contractility in both systems were evaluated using BOOI & BCI and Schäfer nomogram. Patients were obstructed if the BOOI is > 40, equivocal if the BOOI is 20-40, and unobstructed if the BOOI is <20. Regarding the BCI, a strong contractility is a BCI of >150, normal contractility a BCI of 100-150 and weak contractility a BCI of <100. The agreements of Qmax and PdetQmax between two catheter systems were assessed using the Bland and Altman analysis. Cohen’s kappa estimation was used for the agreements of grading of BOO and bladder contractility between them.
Twenty-five male patients were selected to evaluate comparison of WFC and ACC system. The average age was 74.2±5.8 years old. Their symptoms were difficulty on urination 19, incontinence 2, nocturia 2, pollakiuria 2, respectively.
Applying the Bland and Altman method, the values of Qmax are similar (mean differences 0.3ml/s), however, the values of PdetQmax in the WFC systems are higher than that in the ACC (mean differences 4.6cmH2O) (Fig1). There were wide 95% limits for agreement for difference in both Qmax and PdetQmax (-3.9 to 4.5 mL/s and -12.6 to 21.8 cmH2O, respectively). Cohen’s kappa for obstruction and detrusor contractility estimated using BOOI and BCI were 0.802 and 0.696 respectively. Cohen’s kappa for grading of obstruction and detrusor contractility using Schäfer nomogram, were 0.433 and 0.682 respectively (Table 1). Less agreement in Schäfer nomogram may be due to more fine grading compared with that in BOOI and BCI.
Interpretation of results
These findings suggested that PdetQmax in PFS using AFC and WFS system appear to be not interchangeable and Qmax may be interchangeable because of small mean differences. Cohen’s kappa may suggest that the agreement of grading of obstruction and detrusor contractility using BOOI and BCI appeared to be almost perfect and substantial and those using Schäfer monogram appeared to be substantial and moderate.