Simultaneous bladder drainage via suprapubic and urethral catheters: which drains more completely and why?

Simultaneous bladder drainage with urethral and suprapubic catheters shows greater drainage from the suprapubic catheter (35% vs 65%). When using two catheters, both can be placed to gravity to maximize bladder drainage as the suprapubic catheter can drain residual urine not adequately drained by the urethral catheter.