Influence of venous stasis on survival of epigastric flaps in rats.

Venous congestion results in tissue damage and remains the most common reason for failure of transfer of microvascular free flaps if it is not recognised early. The purpose of this study was to measure the critical duration of venous congestion and the resultant survival of flaps according to the duration of venous stasis. A standard epigastric flap was raised and repositioned in 35 rats, seven of which acted as controls. The superficial inferior epigastric vein was fully occluded for four, five, six, or seven hours in the rest (n=7 each group). Subsequently, the rats were monitored for one week, and the resultant necrotic areas were photographed. After five, six, and seven hours of venous stasis, the incidence and area of necrosis were significantly increased (p=0.04 in each) above that of the control. The degree of necrosis after seven hours of venous stasis was significantly greater than that after four or five hours (p=0.01 and 0.02, respectively). The duration of venous congestion is therefore a potential risk for the survival of free flaps, as it results in operative complications and may jeopardise the whole procedure. After a critical period of venous stasis we reach a point of no return, and any attempt to salvage the compromised flap will be in vain. Based on these results, we think that monitoring by an experienced surgeon at intervals of no longer than three hours is essential for the successful salvage of venous congestion in microvascular free flaps.