Effect of cardiopulmonary bypass on urethral blood flow as measured by laser Doppler flowmetry

Purpose: Previous reports have implicated urethral ischemia as a potential predisposing factor for the increased incidence of urethral strictures after cardiac bypass surgery. These reports were based on indirect measurements of urethral blood flow. We directly measured and compared urethral perfusion before and during cardiopulmonary bypass. Materials and Methods: A total of 10 patients undergoing cardiac bypass surgery (mean age 70) and 4 undergoing various surgery without cardiopulmonary 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) compared to pre-bypass levels. Stratification of the patients into warm versus 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 significant decrease in mean flow. There was no significant decrease in urethral blood flow in the nonbypass group. Conclusions: Our study demonstrates that there is decreased blood flow to the urethral mucosa during cardiopulmonary bypass. This finding lends support to the idea of urethral ischemia as a contributing factor in the pathogenesis of urethral strictures following cardiac bypass surgery.