Remote ischemic preconditioning of flaps: a review.

Ischemic preconditioning (IP) is defined as a brief period of ischemia ("preclamping") followed by tissue reperfusion, thereby increasing ischemic tolerance for a subsequent longer ischemic period. Several studies showed the effectiveness of classic local IP by preclamping the flap pedicle. There are two temporally and mechanically different types of IP: acute preconditioning, which is induced by preclamping the flap pedicle briefly before flap ischemia, and late preconditioning, induced by a preclamping procedure 24-48 h before flap ischemia. However, both types of local ischemic preconditioning are rarely used clinically, most likely since they can be applied only by invasive means, significantly increase operation time, or even require a second surgical procedure. Several studies from our laboratory showed, in different experimental models, that acute IP, enhancement of flap survival, and improvement of reperfusion microcirculation can be achieved not only by preclamping the flap pedicle, but also by induction of an ischemia/reperfusion event in a body area distant from the flap prior to elevation. This new acute remote IP procedure can be applied without invasive means, using limb tourniquet ischemia briefly before flap ischemia. The effectiveness of acute remote IP was confirmed by other authors in large animal models. Another of our studies showed that late remote IP using a limb tourniquet 24 h before flap ischemia attenuates ischemia/reperfusion in muscle flaps, whereas it was ineffective in adipocutaneous flaps. The exact mechanism of "classic" as well as remote IP is not yet finally determined, although several studies demonstrated that endogenous nitric oxide plays an important role. In summary, the use of a tourniquet to induce limb ischemia before flap ischemia could provide a new, alternative, noninvasive remote IP protocol, although late remote IP might be effective only in muscle flaps. However, the possible future clinical application for late IP is elective flap surgery, whereas acute remote IP could even be used in emergency flaps.