Flap Monitoring

Monitoring circulation of flaps post-operatively is critical to success in microvascular transplantation.  To be effective, changes in perfusion need to be recognized quickly to correct any treatable problems.  Disruption of perfusion to a flap can result in partial or complete flap loss.  Failure to establish re-perfusion of blood supply after blood vessel repair to an ischemic organ is known as the no-reflow phenomenon.  The mechanism  is believed to be related to blood vessel injury, specifically endothelial injury, as well as platelet aggregation and leakage of intravascular fluid.  The severity of this effect is correlated with ischemia time - the total time the flap lacks perfusion and oxygen flow.  Monitoring and quick recognition of ischemia reduces the chance of a no-reflow phenomenon and flap failure.

Clinical monitoring is effective, but can be difficult, even with the most experienced observer.  Often it can be tricky to tell if a flap has a circulatory problem.  The examiner looks at flap color and sometimes capillary refill or temperature depending on the setting.

Flap circulatory disturbances can be divided into arterial insufficiency and venous insufficiency.  If there is an arterial circulatory problem the flap would usually look pale and lack capillary refill.  Muscle flaps can be particularly difficult to judge – color change with loss of a beefy red appearance is most common.  If venous clot is the cause of flap failure, the flap generally becomes congested and bluish in color.  Capillary refill is brisk.  Sometimes poking a flap with an 18 gauge needle (away from the pedicle site) can help you judge flap circulation.  If there is no bleeding, the problem is inflow.  If there is rapid exit of dark red blood, venous congestion is likely the problem.

More sophisticated devices to monitor flap flow have been developed.  The ideal monitor is reliable, accurate, simple to operative, continuous and inexpensive.  Several different monitoring devices are in use now, and include:

1. Surface or pencil Doppler

2. Temperature probe

3. Laser Doppler probe

4. Quantitative fluorimetry

5. Implantable Doppler probe

The implantable Doppler has been found to be highly reliable with several of the qualities needed for an ideal monitoring system.  In a study performed by Kind et. al. in 1998, the implantable Doppler probe was able to salvage 100% of flaps that were failing due to clotting at an anastomotic site.

The probe is placed on the draining vein of the free flap to monitor venous flow post-operatively.  If flow loss is detected, it may represent venous or arterial clotting in the micro-circulation of the flap and require urgent exploration.