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Effect of cardiopulmonary bypass on urethral blood flow as measured by laser Doppler flowmetry
B R Bamshad1, M W Poon, S C Stewart
1Division of Urology, Loma Linda University Medical Center, California, USA.
Insights
Cardiac bypass surgery significantly reduces urethral blood flow, suggesting urethral ischemia may contribute to stricture formation. This study directly measured blood flow to confirm the link.
Area of Science:
- Urology
- Cardiovascular Surgery
- Medical Devices
Background:
- Urethral strictures are a known complication following cardiac bypass surgery.
- Previous evidence linking urethral ischemia to strictures was indirect.
- Direct measurement of urethral blood flow during bypass was lacking.
Purpose of the Study:
- To directly measure and compare urethral perfusion before and during cardiopulmonary bypass.
- To investigate the role of urethral ischemia in the pathogenesis of post-cardiac bypass urethral strictures.
Main Methods:
- Prospective study of 14 patients (10 cardiac bypass, 4 non-bypass).
- 16F silicone urethral catheter insertion prior to surgery.
- Intraoperative measurement of urethral blood flow using a laser probe (Vasamedics PR-434).
Main Results:
- Cardiopulmonary bypass resulted in a significant 50% average decrease in urethral blood flow (p <0.001).
- Both warm (58% decrease) and cold (44% decrease) cardioplegia strategies reduced flow.
- No significant decrease in urethral blood flow was observed in the non-bypass control group.
Conclusions:
- Direct measurements confirm reduced urethral mucosal blood flow during cardiopulmonary bypass.
- This supports the hypothesis that urethral ischemia is a contributing factor to stricture development after cardiac bypass surgery.
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.