1. The burst of damaging oxygen free-radicals at the time of reperfusion is one of the crucial factors affecting skin flap survival after an ischaemic interval. In these experiments the efficacy of the antioxidant and free-radical scavenger N-acetylcysteine in improving the survival of ischaemic rabbit epigastric skin flaps was tested.

2. At the time of reperfusion flaps were given: (1) balanced salt solution by intravenous whole-body administration, (2) N-acetylcysteine (200 mg/kg) by intravenous whole-body administration, (3) balanced salt solution by intra-arterial infusion into the flap, (4) N-acetylcysteine (20 mg/kg) by intra-arterial infusion into the flap, or (5) N-acetylcysteine (200 mg/kg) by intra-arterial infusion into the flap. Flap survival at 1 week, and tissue levels of parameters related to free-radical production, blood levels of thromboxane B2 and peripheral resistance during reperfusion were determined.

3. Compared with controls (groups 1 and 3) which had flap survival rates (expressed as percentage surface area surviving) of 27.1% and 31.6%, respectively, N-acetylcysteine treatment in group 2 (55.2%) and group 4 (51.9%) resulted in significant (P < 0.05) improvements in flap survival. The survival rate in group 5 (37.7%) was not significantly better than that of the controls.

4. N-Acetylcysteine significantly reduced parameters related to free-radical production in the skin flap after 30 min of reperfusion, determined as tissue levels of malonyldialdehyde and protein oxidation products. There was also a significant decrease in peripheral resistance when low-dose N-acetylcysteine (group 4) was infused intra-arterially into the flap. The systemic levels of thromboxane B2, a prostanoid promoting thrombosis, were not significantly altered by administration of N-acetylcysteine.

5. N-Acetylcysteine proved to be a successful therapeutic agent for the salvage of experimental ischaemic rabbit skin flaps, when used as a low-dose intra-arterial or high-dose intravenous treatment. The possible clinical benefits in humans have yet to be demonstrated.

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