A common cause of free flap and replant failure is thrombotic occlusio
n of the anastomosed pedicle vessel(s). Clinical observations and subs
equent experimental studies showed that platelet emboli generated at t
he arterial anastomosis caused significant alterations in the downstre
am microcirculation. To study both the thrombogenic arterial (anastomo
sis) site and the downstream microcirculation, we developed an animal
model (the isolated rat cremaster) in which we could directly view and
quantitatively analyze thrombus formation and the appearance of embol
i in the downstream microcirculation. Using this model we studied the
effect that reducing blood flow across the arterial anastomotic site h
ad on thrombus formation at the anastomotic site and the appearance of
emboli in the downstream microcirculation. In 40 male Sprague-Dawley
rats we found that reducing blood flow velocity to approximately half
of normal during reperfusion nearly eliminated emboli appearing in the
downstream microcirculation compared with controls, 43.9 +/- 31.5 vs.
259.5 +/- 117.8 emboli, respectively. We also found that the same low
flow had no effect on thrombus size at the pedicle artery injury site
yet significantly decreased the rate at which thrombus formation occu
rred (time to maximum thrombus size; low flow = 25.3 +/- 8 minutes, no
rmal flow = 6.6 +/- 3 minutes). From these studies we conclude that re
ducing pedicle artery blood flow in our rat model during reperfusion c
an protect the downstream microcirculation from platelet emboli-induce
d injury; however, the same reduction in flow does not affect thrombus
formation in the pedicle artery. Further studies using direct observa
tion/measurement techniques are needed for a better understanding of t
he mechanisms regulating free flap and replant failure.