Posterior urethral valves: primary voiding pressures and kidney function in infants

We evaluated whether high voiding pressures in patients with posterior urethral valves are associated with reduced kidney function.

A total of 25 children younger than 12 months with posterior urethral valves underwent urodynamic evaluation within 15 days of valve ablation between 1994 and 2007. Six patients underwent primary urodynamics before and 19 after valve ablation. A total of 17 patients underwent repeat studies after 1 month and 1 year. Maximum detrusor pressures during voiding and cystometric bladder capacity were compared with kidney function tests. Maximum detrusor pressures during voiding was compared with a control group and data from other studies of male infants.

At presentation median cystometric bladder capacity was 22 ml (range 5 to 125) and maximum voiding pressure was 112 cm H(2)O (40 to 331). There was no statistical difference in bladder capacity and voiding pressures before and after valve ablation. Also, patients with and without vesicoureteral reflux had similar bladder capacities and voiding pressures. There was no association between primary voiding pressures and serum creatinine levels or kidney split function during the first year of life. Primary voiding pressures were about the same as in a control group and in previous studies of males who were healthy, who had reflux or whose status was post-pyelonephritis. Voiding pressures had decreased and bladder capacity had increased significantly at 1-year followup.

Voiding pressures in infants with posterior urethral valves are as high as but not higher than other male infants. High voiding pressures postnatally are not associated with reduced kidney function.