**5. Couple devices**

Since the onset of microsurgery, a great interest was drawn towards the development of suture techniques to perform anastomoses more quickly and automatically, in order to buffer inaccuracies [28]. For this purpose, devices in the form of two metal rings that are coupled, known as coupler devices, were developed.

Currently, its use is widespread, mainly for vein anastomoses, although they have also tested a 100% patency in arterial ones. The vessel is introduced through the ring and the edges are fixed inside-out in the pins arranged in the ring, then the same is done with the other vessel and the hinge of the device, that joins both sides, is closed. The eversion of the edges achieves less exposure of the vascular lumen to foreign

material and therefore the rate of thrombogenesis is lower. This eversion of the edges in the case of the arteries is more complex due to the thickness of the vascular wall, which makes its use in arterial anastomosis not so popular [28, 30]. There are coupler devices currently available with built-in systems for flap control, such as Doppler.

Despite their many advantages, they present some drawbacks. Although they have been shown to reduce the time needed to perform the anastomosis, their use involves some complexity and produces some stenosis. On the other hand, they are not recommended in areas with a tendency to infection, with poor vascularisation or to be irradiated.
