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Post-Hoc Tracing Interpretation Does Not Reliably Detect Artifactual Depression of Detrusor Pressure Due to Rising Abdominal Pressure Readings in Pediatric Urodynamics
Eric Nelson, MD, Gillian Wolff, MD, Renee Silvis, M.Sc., Christine Kim, MD, John Makari, MD, Fernando Ferrer, MD, Phillip Smith, MD.
Connecticut Children's Medical Center; University of Connecticut School of Medicine, Hartford, CT, USA.
BACKGROUND: Gradual increases in measured abdominal pressure (Pabd) during bladder filling are commonly observed in pediatric urodynamics. Thus, detrusor pressure (Pdet) by standard calculation (Pves-Pabd) at the end of bladder filling has been found to be significantly less than a modified Pdet calculated as the rise in passive Pves during filling. This could potentially provide false reassurance of low-pressure urine storage. We hypothesized that this potential error would be reliably recognized on the urodynamic tracing in the absence of cursor-driven numerical data extraction from the electronic urodynamic pressure recording.
METHODS: 160 sequential urodynamic studies were examined. Tracings from 149 were available for review. The standard Pdet calculation and the rise in passive Pves during filling were determined using the data cursor at the urodynamic console, and the difference (Gap) calculated. 3 reviewers blinded to the electronic results (a urology resident, a pediatric urologist, and an experienced urodynamicist) categorized the printed summary tracings into two categories: I: Pabd flat during filling, II: Pabd rises during filling. Cohen kappa was used to test observer reliability (tracing vs. cursor calculation) and inter-observer (tracing vs tracing) of the categorizations.
RESULTS: Reliabilities of post-hoc determination of potential error in Pdet determination were fair-moderate, all p<0.001. Mean kappa = 0.567 +/- 0.022 for interobserver reliability (moderate), 0.446 +/-0.057 (moderate) for observer vs. Gap >10 and 0.306 +/-0.034 (fair) for observer vs. Gap>2.
CONCLUSIONS: Post-hoc interpretation of urodynamic tracings does not provide good reliability for the detection of gradual increases in Pabd. Reservoir pressures may therefore be underestimated by standard Pdet calculation. The ability to time-expand the urodynamic record and the availability of a data cursor facilitate the detection of the potentially rising Pabd during filling and the subsequent erroneous lowering of Pdet by standard calculation.
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