Normal ranges of variability for urodynamic studies of neurogenic bladders in spinal cord injury

Background/Objective: Urodynamic studies are conducted on a regular basis to evaluate changes in bladder function after spinal cord injury. Often, differences in urodynamic parameters exist from one study or one year to the next. The objective of this study was to provide reference ranges for "normal" variability in urodynamic parameters that can be considered as "no real change" from one study to the next. Design: Retrospective chart review. Methods: Fifty consecutive individuals with spinal cord injury had 2 trials (trial 1 and trial 2) of urodynamic studies done 5 minutes apart, and the following data were collected: maximum cystometric capacity, opening pressure, maximum detrusor pressure, volume voided, and postvoid residual. The corresponding data were compared, and the frequency distribution for the change between consecutive studies was plotted. Because there is no standard, variability ranges for 5th to 95th, 10th to 90th, and 25th to 75th percentiles were calculated to give health care providers more choices. Results: Ranges of variability are as follows in the following format (urodynamic parameter; mean value; maximum increase; -, maximum decrease)-5th to 95th percentile: cystometric capacity (234.63 mL, + 213.50 mL, -158.05 mL); opening pressure (54.56 cmH(2)O,+30cmH(2)O, -18.00 cmH 2 0); maximum detrusor pressure (60.82 cmH(2)O, +17.35 cmH(2)O, -27.80 cmH(2)O); volume voided (122.20 mL, +177.25 mL, -176.00 mL); postvoid residual (176.06 mL, + 197.25 mL, -118.00 mL); 10th to 90th percentile: cystometric capacity (234.63 mL, +126.40 mL, -74.60 mL); opening pressure (54.56 cmH(2)O, +13.70 cmH(2)O, -12.00 cmH(2)O); maximum detrusor pressure (60.82 cmH(2)O, +10.00 cmH(2)O, -20.00 cmH(2)O); volume voided (122.20 mL, +105.60 mL, -82.00 mL); postvoid residual (176.06 mL, +131.00 mL, -86.00 mL); 25th to 75th percentile: cystometric capacity (234.63 mL +72.00 mL, -27.00 mL); opening pressure (54.56 cmH(2)O, + 4.00 cmH(2)O,-9.50 cmH(2)O; maximum detrusor pressure (60.82 cmH(2)O, + 4.00 cmH(2)O, -10.00 cmH(2)O); volume voided (122.20 mL, + 50.00 mL, -30.00 mL); postvoid residual (176.06 mL, + 50.00 mL, -30.00 mL). Conclusions: Urodynamic studies have variability. Knowing these ranges of variability can be helpful in determining whether differences between filling trial 1 and filling trial 2 in a single study or year-to-year changes in urodynamic studies are significant or simply the normal variability of the urodynamic study.