Accuracy of Measuring Bladder Volumes With Ultrasound and Bladder Scanning

Abstract

Background Removal of urinary catheters depends on accurate noninvasive measurements of bladder volume. Patients with acute kidney injury often have low bladder volumes/ascites, possibly causing measurement inaccuracy. Objective To evaluate the accuracy of bladder volumes measured with bladder scanning and 2-dimensional ultrasound (US) compared with urinary catheterization among different types of clinicians. Methods Prospective correlational descriptive study of 73 adult critical care patients with low urine output receiving hemodialysis or unable to void. Bladder volumes were independently measured by (1) a physician and an advanced practice registered nurse using US, (2) an advanced practice registered nurse and a bedside nurse using bladder scanning, and (3) urinary catheterization (cath). Bland-Altman and χ2 analyses were conducted. Results Mean (SD) cath volume was 171.7 (269.7) mL (range, 0-1100 mL). Abdominal fluid was observed in 28% of patients. Bias was −1.3 mL for US vs cath and 3.3 mL for bladder scanning vs cath. For patients with abdominal fluid and cath volume less than 150 mL, decisions to not catheterize patients were accurate more often when based on US measurements (97%-100%) than when based on bladder scanning measurements (86%-89%; P = .02). In patients with cath volume of 300 mL or more, decisions to catheterize patients were accurate more often when based on bladder scanning measurements (94%-100%) than when based on horizontal US measurements (50%-56%; P = .001). Conclusions Bladder volume can be measured accurately with bladder scanning or US, but abdominal fluid remains a confounding factor limiting accuracy of bladder scanning.