Validation of 3-dimensional mathematical computation of feline bladder volume using orthogonal ultrasonographic bladder images.

Urine output measurement is critical for the management of hospitalized cats and their underlying conditions. Ultrasound-guided estimation of urinary bladder volume (UBV) is a non-invasive surrogate measurement that can provide important clinical information. The purpose of this study was to validate the accuracy of a novel 3D computation method in estimating UBV using 2D point-of-care ultrasonographic images. Bladder volume estimation was performed using coordinates from bladder circumference tracings on paired longitudinal and transverse ultrasonographic images (n = 359) aligned in 3D space for mathematical algorithmic computation. Ultrasonographic images were obtained by 2 different observers at 18 different time points on 10 healthy, purpose-bred male cats under general anesthesia in sternal recumbency. Actual urine volumes were measured via urinary catheterization and compared to UBV estimations using Lin's concordance correlation coefficient and Bland-Altman analysis. Estimation of UBV using the 3D computational bladder circumference tracing method showed moderate strength-of-agreement with actual bladder volume (ρ_c = 0.94 to 0.95) with clinically insignificant bias (3D computation-derived minus actual volume) of -1.96 mL (IQR = -3.89 to -0.57 mL, P < 0.001) and -2.42 mL (IQR = -4.64 to -0.66 mL, P < 0.001) for the 2 observers, respectively. Our study demonstrated acceptable accuracy of 3D computation method for UBV estimation in healthy cats. This method may provide a bridging alternative until 3D ultrasound becomes more readily accessible.