EFFECT OF CARDIOPULMONARY BYPASS ON URETHRAL BLOOD-FLOW AS MEASURED BY LASER-DOPPLER FLOWMETRY

Purpose: Previous reports have implicated urethral ischemia as a poten tial predisposing factor for the increased incidence of urethral stric tures after cardiac bypass surgery. These reports were based on indire ct measurements of urethral blood flow. We directly measured and compa red urethral perfusion before and during cardiopulmonary bypass. Mater ials and Methods: A total of 10 patients undergoing cardiac bypass sur gery (mean age 70) and 4 undergoing various surgery without cardiopulm onary bypass (mean age 54) were studied prospectively. A 16F silicone urethral catheter was placed in each patient before surgery. Urethral blood flow was measured intraoperatively using the Vasamedics PR-434 implantable prism laser probe before and during cardiopulmonary bypass . Results: In the patients undergoing cardiopulmonary bypass there was an overall 50 +/- 28% decrease in flow (range 0 to 88%, p <0.001) com pared to pre-bypass levels. Stratification of the patients into warm v ersus cold cardioplegia revealed a mean percent decrease in flow of 58 +/- 20% (range 41 to 87%, p <0.05) for the warm and 44 +/- 33% (range 0 to 88%, p <0.05) for the cold group. Only 1 bypass case showed no s ignificant decrease in mean flow. There was no significant decrease in urethral blood flow in the nonbypass group. Conclusions: Our study de monstrates that there is decreased blood flow to the urethral mucosa d uring cardiopulmonary bypass. This finding lends support to the idea o f urethral ischemia as a contributing factor in the pathogenesis of ur ethral strictures following cardiac bypass surgery.