Secondary ischemia caused by venous or arterial occlusion shows differential effects on myocutaneous island flap survival and muscle ATP levels

Ischemia-reperfusion injury is one of the major problems in reconstructive microsurgery. The ischemic insult may be due to an occlusion of either the artery or the vein. Clinical observations have suggested that flap survival is more sensitive to venous stasis than to arterial ischemia. The current study evaluated the viability of the myocutaneous rectus abdominis flap following secondary arterial or venous occlusion and its possible dependency on tissue metabolites and length of the preceding reperfusion period. Forty-eight bilateral 5 x 10 cm myocutaneous rectus abdominis flaps were elevated in 24 pigs and exposed to consecutive periods of primary ischemia (2 hours), reperfusion (1, 4, 8, and 12 hours), and secondary pedicle occlusion (6, 8, 10, 12, 14, or 16 hours) of arterial or venous origin. Muscle adenosine triphosphate (ATP) and glucose-6-phosphate (G6P) were assessed immediately after flap elevation, at the end of primary ischemia, after reperfusion, and at the end of secondary ischemia. Flap viability, was assessed 5 days after the operation. Secondary venous occlusion resulted in reduced survival rates as compared with arterial occlusion (9 of 24 versus 20 of 24; p < 0.01), although the average ATP content was higher in flaps subjected to venous stasis [median (25 to 75) percentiles, 3.7 (1.7 to 7.1) μmol/gm protein] than in those subjected to arterial ischemia 1.2 (0.8 to 1.8 μmol/gm protein) (p < 0.01). During reperfusion, muscle ATP decreased from 28.5 (17.9 to 36.6) μmol/gm protein to 15.4 (7.4 to 24.9) μmol/gm protein (p < 0.01) and glucose-6-phosphate from 7.6 (4.1 to 11.6) μmol/gm protein to 1.0 (0.5 to 4.1) μmol/gm protein (p < 0.0l). Still, flap survival following secondary arterial ischemia was improved by increasing the reperfusion time from 1 to 8 hours (p < 0.05). No effect of reperfusion time was seen on viability after venous stasis. In conclusion, despite poorer flap survival, venous stasis was less detrimental to tissue ATP level, suggesting that the continued inflow may have supplied substrates for glycolysis. Furthermore, the larger blood volume may have accumulated the glycolytic waste products. After reperfusion, the recovery of aerobic metabolism was far from complete, and cellular glycolytic substrates were nearly exhausted. However, prolongation of the reperfusion time preceding secondary arterial ischemia improved flap survival.