Evaluation of a non-invasive bladder volume measurement in children

Objective. Postoperative urinary retention (PUR) is associated with overdistension of the bladder. The prevention of PUR by routine catheterization may increase the risk of urinary tract infection. Postoperative monitoring of the bladder volume by ultrasound to prevent PUR is reliable in adults, but has not been evaluated in children. Material and methods. The BladderScan® BVI 6200, an ultrasound device specifically designed for children, was assessed. Forty patients who required urinary catheter placement during surgery or during intensive care unit stay were entered into this blinded calibration study. An assessment of bladder urine volume by ultrasound was performed before and after catheterization in surgical patients. In these patients and intensive care patients 0, 2.5 or 5 ml/kg sterile normal NaCl was injected through the bladder catheter and the catheter was clamped. Volumes estimated with ultrasound were compared with measured catheter drainage or/and injected volume after the scan. Results. The mean relative difference (bias) between the ultrasound estimate and the injected volume was -20% (95% confidence interval 140 to -180%). Precision, estimated using the Wilcoxon signed ranks test, showed a significant difference (Z=-3.25, p=0.001) between the ultrasound-estimated volumes and the injected volumes. Conclusions. This study could not confirm good agreement between the ultrasound-estimated volumes and the injected volumes at volumes below 5 ml/kg. Bladder volumes were underestimated with a very broad 95% confidence interval. The ultrasound device should not replace current clinical assessment.