What is the variability between 2 consecutive cystometries in the same child?

We compared the results of 2 cystometrograms (CMGs) performed during a single session in the same child to determine the variability between consecutive cystometries.

Subjects underwent 2 consecutive bladder fillings performed at the same rate and position. Maximum cystometric bladder capacity (CBC), pressure at CBC, leak point pressure, maximum flow rate, pressure at maximum flow, maximum voiding pressure, residual urine and pressure specific volumes (PSV) less than 20, 30 and 40 cm water were compared between studies. Uninhibited detrusor contractions (UICs), defined by the previous and new International Children's Continence Society definitions of UIC, were also compared. Data were analyzed using paired t test, chi-square and interclass correlation.

CMGs in 32 male and 34 female children were available for analysis. Mean subject age was 7.4 years (range 1 month to 18 years). Of the children 43 (65%) had spinal dysraphism, 4 (6%) had cerebral palsy, 5 (8%) had posterior urethral valves, and 14 (21%) had recurrent urinary tract infection, daytime incontinence and frequency/urgency symptoms. Maximum CBC, pressure at CBC, leak point pressure, maximum flow rate, pressure at maximum flow, maximum voiding pressure and residual urine did not differ between the 2 studies. PSVs less than 20, 30 and 40 cm water were highly correlated between the 2 CMGs (interclass correlation coefficients 0.795, 0.683 and 0.850, respectively). There were more UICs on the first than the second study (p = 0.02 and 0.03) as defined by the previous and new definitions of UIC. UIC threshold volume was less on the first CMG (p = 0.00 and 0.03). UICs were either present or absent on both studies in 56 of the 66 (85%) children by the previous UIC definition and in 51 (77%) by the new UIC definition.

There is no difference in CBC, PSV and pressure flow parameters when performing consecutive urodynamic studies in the same child. However, UICs are more frequent on the first study. We conclude that repeat cystometry is not indicated in the absence of UICs on the first study and suggest that the second consecutive CMG be used for clinical interpretation when repeat studies are performed in the same session.