Ultrasonographic assessment of bladder volume prior to urinary catheterization in infants: Training operators and avoiding unsuccessful catheterizations

Abstract

Study objectives: Previous studies have shown a 10% failure rate in urine catheterization in children younger than 2 years. This leads either to an incomplete evaluation or a second procedure, with attendant discomfort for child and parent and increased risk of urethral trauma. We assess a brief educational intervention to teach pediatric and emergency medicine attending physicians and residents to use ultrasonography to measure a bladder index and attempt to define a minimum index predictive of successful catheterization. Methods: Investigators were given a 30-minute training session on identifying and measuring the urinary bladder with ultrasonography on volunteer patients. All sonograms were performed with a Sonosite iLook with 7.5-MgHz vascular probe. Female patients younger than 2 years and male patients younger than 1 year were enrolled prospectively in an urban pediatric emergency department during a 1-month period. The physicians performing the catheterization were blinded to the sonographic results. Data recorded were demographics, anterior posterior and lateral bladder diameter, success in obtaining 2 mL of urine (the minimum needed to guarantee urine analysis and culture) and complicating factors. Bladder index was defined as the product of anterior posterior and lateral diameters, expressed in square centimeters. Assuming a perfect sphere, a bladder radius of approximately 0.75 cm would equal a volume of 2 mL. Using this model, the equivalent bladder index would be 2.2 cm². We expect bladder indices roughly at or above this cutoff to be successful. Results: Twenty patients were enrolled, 11 of whom were girls, average age 7 months, average weight 19 pounds. More than 2 mL of urine were obtained in 16 (80%) patients. These patients had an average AP diameter of 1.9 cm (range 0.7 to 2.8 cm), a lateral diameter of 2.6 cm (range 2.0 to 4.3 cm), and an average bladder index of 4.9 cm² (range 2.2 to 9.4 cm²). Two failures had anterior posterior diameters of 0.5 and 0 and lateral diameters of 0.5 and 0 (bladder indices of 0.25 and 0). The 2 remaining failures were ascribed to the child urinating during the procedure, and repeated catheterization was not performed. Conclusion: Our results indicate that emergency and pediatric attending physicians and residents can be quickly trained to use ultrasonography to assess infant urinary bladders and calculate a bladder index. Our data suggest that a bladder index of 2.2 cm² can be used as a cutoff to predict successful catheterization.