E-Posters-Can We Trust the Math: A Quality Assurance Project Evaluating the Validity of Postvoid Residual Estimation by Subtraction

Can We Trust the Math: A Quality Assurance Project Evaluating the Validity of Postvoid Residual Estimation by Subtraction - Anna M Drewry, MD

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This study evaluated the validity of estimating postvoid residual (PVR) volume by subtraction in postoperative urogynecology patients. The normal range for PVR is 30-100 mL, and catheterization is considered the most accurate measurement method. In this study, seven patients who had elevated PVR during initial retrograde fill voiding trials (VTs) had their catheters replaced and underwent VTs performed by a urogynecology clinic nurse. Saline was instilled via gravity, and PVR was calculated by subtracting the voided volume from the instilled volume. PVR was also assessed using ultrasound followed by catheterization.<br /><br />The results showed that PVR calculated by subtraction was within 100 mL of PVR obtained by catheterization in 71% of cases. However, two patients had significant discrepancies of 250 mL and 140 mL. The interpretation of PVR as normal or elevated changed for three patients (43%) when assessed with catheterization instead of subtraction. If subtraction alone had been used to assess PVR, two patients would have been misdiagnosed with normal PVR when their true PVRs were elevated.<br /><br />The study concludes that the subtraction method is limited in assessing PVR and suggests that a more rigorous research approach should be applied to this question. This has implications for algorithms used in trials such as the Trial Of Mid-Urethral Slings (TOMUS), as the two patients with elevated PVR by catheterization but not by subtraction would have been misclassified. The authors recommend further research on this topic.<br /><br />In summary, this quality assurance project highlights the limitations of using the subtraction method to assess PVR in postoperative urogynecology patients. Subtraction does not provide a valid assessment of PVR in this population, and a more rigorous research approach is necessary.

Keywords

postvoid residual

PVR volume

urogynecology patients

catheterization

retrograde fill voiding trials

instilled volume

ultrasound

discrepancies

misdiagnosis

research approach