Blood-flow velocity as a factor in postoperative microvascular patency.

The authors attempted to develop a reliable and reproducible new animal model in which the blood-flow velocity to a flap could be varied. This model was utilized to study the effects of different blood-flow velocities on the patency rate of small 1- to 2-mm vessels after common microsurgical procedures. Male Sprague-Dawley rats, weighing 450 to 550 gm, were used to develop a model creating either a "high blood flow" or a "low blood flow" state by ligating the rat femoral artery, either distally or proximally, to an epigastric artery based on a groin cutaneous flap. Blood-flow velocities were measured by microvascular flowmeter, and statistical analysis was performed on the data collected. The model was next used to determine the effects of different blood-flow velocities on the patency rates of rat femoral vessels after primary anastomosis vs interpositional vein grafting. Interpositional vein grafting was subsequently repeated by a more senior microsurgeon, to determine the potential effects of increased surgical experience. The animal model was reliable, easily reproducible, and efficacious in producing two separate groups of rats with significantly different blood-flow velocities (3.98 vs. 2.14 +/- 0.5 ml/min), as was confirmed by electromagnetic flowmeter and statistical analysis. In experienced hands, decreased blood-flow velocity did not result in decreased patency rates of these small vessels after primary anastomosis, or even after vein grafting. As long as microvascular vein grafting and primary anastomosis procedures are done properly, even 1-mm vessels can tolerate significantly decreased blood-flow velocity without a decreased patency rate. Although many known factors can contribute to thrombosis and failure of anastomoses in clinical microsurgery, blood-flow velocity appears not to be a significant factor. Also described is a new, reliable animal model that can be used in small-vessel blood-flow velocity studies.