Michael J. Im

The role of oxygen-free radicals in ischemic tissue injury in island skin flaps.

The contribution of free radical-mediated reperfusion injury to the ischemic damage caused by total venous occlusion of island skin flaps was investigated in a standardized rat model. Control flaps subjected to 8 hours of total venous occlusion showed complete, full thickness necrosis when followed for 7 days following release of the vascular occlusion. Treatment with superoxide dismutase, a scavenger of superoxide radicals, prior to and immediately following the onset of reperfusion, significantly enhanced island flap survival from 0/11 (0%) to 8/15 (53%), p < 0.005, and from 0/9 (0%) to 6/12 (50%), p < 0.02, respectively. These findings are consistent with the hypothesis that oxygen free radicals generated at the time of reperfusion following a period of ischemia contribute significantly to the ultimate damage caused by ischemic injury. Such findings are consistent with similar reported observations on other tissues and suggest a means by which ischemic tissue injury might be therapeutically modified, even after the period of ischemia.

Effects of superoxide dismutase and allopurinol on the survival of acute island skin flaps

We have demonstrated previously that oxygen-derived free radicals are important mediators of tissue injury following ischemia (total venous occlusion) and reperfusion in small (3 cm X 6 cm) island skin flaps in rats. In this study, we evaluated extension of this concept to regional ischemia in large (8 cm X 8 cm) acute island skin flaps which were constructed to exceed their sole blood supply via unilateral inferior epigastric vessels. Under normal (control) circumstances, a significant portion of the flap would undergo necrosis at the periphery, mimicking the corresponding clinical situation. Blocking the generation of superoxide radicals from xanthine oxidase with a single dose of allopurinol prior to flap elevation significantly improved the area of flap viability from 34 +/- 12% to 57 +/- 6% (p less than 0.01) in the random portion of the flap, contralateral to the source of blood supply. Similarly, the detoxification of superoxide radicals with a single dose of superoxide dismutase improved viability from 41 +/- 6% to 58 +/- 7% (p less than 0.01). Similar results were obtained when either of these agents were administered 60 minutes after flap elevation. These findings suggest that oxygen-derived free radicals play an important role in the development of tissue necrosis in the critical transition zone between well-vascularized and devascularized skin.

Effect of allopurinol on the survival of hyperemic island skin flaps

Allopurinol was investigated in 3 x 6 cm congested island skin flaps in rats. Eight hours of venous occlusion produced total flap necrosis. Pretreatment with systemic allopurinol, an inhibitor of xanthine oxidase, enhanced the survival rate of hyperemic skin flaps. Xanthine oxidase activities were demonstrated in skin, and these enzyme activities were noted to increase in skin flaps during ischemia and reperfusion. Much of this increase in enzyme activity was prevented by allopurinol treatment. The xanthine oxidase system appears to be one of the sources of the superoxide radical, which may be involved in ischemic and reperfusion injury in skin.

Tissue Glucose and Lactate Following Vascular Occlusion in Island Skin Flaps

Neurovascular island skin flaps were elevated in the right groin area of Sprague-Dawley female rats weighing from 200 to 250 gm. Survival rates of the flaps were determined following venous and/or arterial occlusions of the femoral vessels. All the flaps exhibited an 80 percent decrease in tissue glucose content and an increase in tissue lactate content 4 to 7 times normal during venous and/or arterial occlusion. In the groups occluded for 8 hours, venous occlusion resulted in loss of all the flaps; arterial occlusion yielded survival of 70 percent of the flaps; and occlusion of both vessels yielded survival of 30 percent of the flaps. The results indicate that venous occlusion is more detrimental to flap survival than arterial occlusion. Surviving flaps exhibited a glucose content of 3.5 times normal, and dying flaps exhibited a glucose content of 20 percent of normal and a lactate content of 5.1 times normal. The ratio of tissue lactate to glucose may serve as an index for tissue viability: normal flaps, 0.3, surviving flaps, 1.2, and dying flaps, 7.5.

Fixation of the craniofacial skeleton with butyl-2-cyanoacrylate and its effects on histotoxicity and healing

&NA; Butyl‐2‐cyanoacrylate is an easily applied, biocompatible, bioresorbable polymer glue that provides an alternative to conventional rigid fixation techniques. Our aim was to determine if cyanoacrylate fixation of the bone flap in a rabbit craniotomy model provides the healing and strength afforded by plate and screw fixation. We also investigated the inflammatory responses of adjacent tissues including the scalp, cranium, and brain. A unilateral parietal bone flap was elevated in 33 adult New Zealand rabbits. The bone was fixed in position with cyanoacrylate (n = 13), fixed with a microplate and screws (n = 14), or was replaced without fixation (sham‐control, n = 6). Normal scar formation and no residual polymer were found in scalp specimens. Neuropathologic analysis identified the presence of residual polymer on the surface of 2 of the 13 rabbit brains. Histopathologic analysis of the bone flap‐to‐skull interface revealed no difference in the degree but rather in the quality of inflammation and healing between the plate and screw and polymer fixation groups. Microdensitometric analysis of the bone gap revealed nearly equivalent bone density in the cyanoacrylate and plated groups, tending to less density in the sham group (p = 0.11 and 0.09, respectively). An additional study focusing on neurotoxicity was performed in 20 adult rabbits with 3‐week and 11‐week recovery periods and similarly found the absence of a marked inflammatory response to the polymer. In conclusion, bone healing and soft‐tissue inflammation were comparable between cyanoacrylate and plate and screw fixation groups. Although butyl‐2‐cyanoacrylate glue fixation may provide a reasonable alternative to hardware fixation, further investigations are necessary to identify its ideal utilization. (Plast. Reconstr. Surg. 102: 309, 1998.)

Effects of Hyperbaric Oxygen and Hyperbaric Air on the Survival of Island Skin Flaps

The effects of hyperbaric air and oxygen on skin survival were studied in acute 8 X 8 cm neurovascular island flaps in rats. Skin flaps treated with hyperbaric 8% oxygen (equivalent to room air at standard pressure) exhibited no improvement in skin survival. Skin flaps treated with hyperbaric air (21% oxygen) and hyperbaric 100% oxygen exhibited significant increases in survival.

The Effect of Bovine Basic Fibroblast Growth Factor on Skin Flap Survival in Rats

Basic fibroblast growth factor (bFGF) was prepared from bovine pituitary glands and evaluated for its effect on the viability of pedicle skin flaps in rats. Pedicle flaps measuring 3 × 7.5 cm and based cephalad were created on the backs of animals. The treatment group received bFGF in saline solution intradermally by Dermo-jet injection 30minutes before flap elevation. Skin flaps treated with a single application of 80 U of bFGF demonstrated a significant increase in viability from 40.8% to 69.7% of the flap area (p<0.001); the flaps treated with 16 U of bFGF exhibited little improvement. Intradermal administration of bFGF to pedicle skin flaps produced an increase in viability that approximates the increase obtained by a surgical delay procedure; treatment of flaps with exogenous bFGF may offer advantages over surgical delay procedures.

Effects of hyperbaric oxygen preservation on rat limb replantation: a preliminary report.

The effect of hyperbaric oxygen, administered during storage, on the survival of replanted limbs was evaluated in rats. The right hindlimbs of male Sprague-Dawley rats were severed and were replanted by microvascular anastomoses after storage in either room air or hyperbaric oxygen (100% oxygen at 2.9 atm absolute) at 23°C for 5 hours. The administration of hyperbaric oxygen during storage improved limb survival from 50% in the room-air, control rats to 100% (p < 0.05). The gastrocnemius muscle of limbs treated with hyperbolic oxygen demonstrated a higher level of energy reserves (creatine phosphate, adenosine triphosphate, glycogen, and glucose) than the same muscle in room-air, control rats. The mechanisms of the beneficial effect of hyperbaric oxygen on limb survival appears to be related to preservation of high-energy phosphates and glycogen.

Increased Survival of Island Skin Flaps by Systemic Heparin in Rats

The effects of systemic heparin on the survival of island skin flaps have been evaluated. Island flaps measuring 3x6 cm were created in the abdomen/groin of rats based on an inferior epigastric neurovascular pedicle. The venous drainage from the flap was occluded for various lengths of time ranging from 5 to 10 hours in the control rats and from 8 to 15 hours in the hours aria-treated group of rats. The rats in the treated group received 1 ml of heparin solution (300–400 U/ kg) through the contralateral saphenous vein immediately prior to the onset venous occlusion and an equivalent dose every 4 hours during venous occlusion. The group of control rats received 1 ml of saline solution. Flap survival was evaluated daily for 7 days. The flaps of control rats demonstrated a gradual decline of the survival rate after 6 hours of venous occlusion and no survival after 10 hours of venous occlusion. The flaps of heparin-treated rats exhibited complete survival until 12 hours of venous occlusion and no survival after 13 hours of venous occlusion. Thus, systemic heparin prolonged tissue tolerance to venous occlusion from 10 to 13 hours. The flaps of control rats demonstrated a significant accumulation of inosine plus hypoxanthine to 260% of normal after 8 hours of venous occlusion. The flaps of heparin-treated rats exhibited little alteration of inosine plus hypoxanthine, and contained a greater concentration of glucose and lactate than the flaps of control rats after 8 hours of venous occlusion. The results demonstrate that systemic heparin can increase tissue tolerance to venous occlusion and improve significantly the flap survival following subsequent reperfusion.

Effects of deferoxamine on ischemia/reperfusion injury after peripheral nerve compression

We have demonstrated previously that acute nerve compression produces ischemia/reperfusion injury in rat sciatic nerve. In this study, we evaluated the effects of deferoxamine, an antioxidant, on recovery from ischemia/reperfusion injury after nerve compression. The sciatic nerves of male Sprague-Dawley rats, 370 to 430 g, were subjected to 24 hours of compression with Silastic tubing. The control group received intravenous saline solution at the time of decompression. The therapeutic group received intravenous deferoxamine (50 mg per kilogram) at the time of removal of the Silastic tubing. Nerve tissues within and distal to the compression site were assayed for malondialdehyde (MDA) levels and for growth-associated protein 43 (GAP-43) expression, as markers of ischemia/reperfusion injury and nerve regeneration, respectively. In the control group (injury alone), the MDA levels were three times higher than normal during the initial 10 days and returned to normal by 14 days. In contrast, the deferoxamine treatment group had MDA levels that were not significantly different from precompression levels. In the control group, enhanced GAP-43 expression persisted until late in the recovery period. In the deferoxamine treatment group, the increased GAP-43 expression subsided early. The results suggest that the treatment of compressed peripheral nerve with deferoxamine at the time of surgical decompression reduces ischemia/reperfusion injury.