Zeroing Pressures in Urodynamics: Revisiting Current Practice and Pressure Interpretation

INTRODUCTION: Zeroing of pressure transducers is a fundamental step in urodynamic testing, as it affects pressure tracings and numerical values. Atmospheric zeroing before catheter insertion is the recommended approach, but zeroing with catheters in situ is also used. We reviewed the conceptual and practical basis for atmospheric zeroing and explored whether in vivo zeroing affects interpretation. METHODS: A structured literature review in PubMed and SciELO (1968-January 2025) identified studies on zeroing techniques and standardization in urodynamics. From 122 records, 20 met predefined criteria for qualitative synthesis, supplemented by key methodological documents. Additionally, three illustrative urodynamic assessments-a woman with stress incontinence, a man with lower urinary tract symptoms, and a patient with neurogenic dysfunction-underwent two consecutive studies (atmospheric and in vivo zeroing) in the same session to compare tracings and derived parameters. RESULTS: The literature describes atmospheric zeroing before catheter insertion as the conventional approach, but no studies were found comparing atmospheric and in vivo zeroing. Conceptual arguments in favor of atmospheric zeroing include interpretation of resting pressures, inter-center comparability, patient-related influences, early measurement artifacts, and voiding-phase considerations. These arguments were not supported by available outcome data, and their clinical relevance was questioned on methodological and practical grounds. In the illustrative cases, both zeroing methods produced different absolute baseline values but similar detrusor pressures, key indices (bladder outlet obstruction index and detrusor overactivity leak point pressure), and unchanged diagnostic and management conclusions. CONCLUSION: The recommendation of atmospheric zeroing rests on conceptual arguments and lacks comparative outcome data. Our synthesis suggests that, in water-filled external-transducer systems, both atmospheric and in vivo zeroing appear capable of producing sound urodynamic studies. Future research should assess their diagnostic agreement, user experience, and the clarity of pressure tracings.