Compromised Skin Grafts and Flaps: Reconstructive Work
Pathophysiology and Hyperbaric Effects
Skin grafts and compromised skin flaps represent a classical problem involving insufficient oxygen supply to tissue. Plastic surgeons use the grafts and flaps to repair serious damage, and to close or cover wounds. In creating skin grafts or flaps, a strip of skin is sharply removed from all or part of its adjacent tissues. The surgery removes all of the blood supply from the skin graft, and eradicates much of the blood supply in the skin flap. Reinisch described such alterations of blood supply and clinicians consider these changes daily in their practices.
Skin grafts are especially susceptible to hypoxic injury. Once a graft is in place, the bed and the edges of the graft site provide the only sustenance available until neovascularization occurs. Hyperbaric oxygen therapy (HBOT) maximizes oxygen transfer for these sites. HBOT ameliorates vascular problems triggered by hypoxia. Three of the primary effects of HBOT, hyperoxygenation, edema reduction, and neovascularization, prove particularly useful to surgeons and plastic surgeons.
Providing hyperoxgenation increases the oxygen tension in the graft bed and wound margins up to 1500 percent. In turn, the hyperoxygenation causes a marked increase in the effectiveness of the blood or plasma that reaches the graft through compromised blood vessels. The volume of tissue that derives sufficient oxygen from a single damaged blood vessel increases 16 fold, and marked tissue salvage results. This same effect, with the augmentation of neovascularization described below, maximizes the rate new blood vessels mature at the site where the graft ultimately attaches.
Hyperbaric techniques also offer strategies for reducing edema. The edema reduction effect, induced by the relative spasm of a precapillary arteriolar sphincter, helps to limit the swelling of the graft or flap. In addition, an increase in the mean diffusion radii occurs, resulting in the amount of tissue being supplied with oxygen increasing significantly. The high oxygen tensions achievable with HBOT induce large oxygen gradients, increasing macrophage migration, proline synthesis, and neovascularization. Once this neovascularization occurs, the beneficial effects of HBOT for organs begins. Among other things, fluids begin to flow to tissues and organs more readily, limiting damage from reperfusion injury.
Both animal and human studies support concepts described above. Jurrel and Kaisjer used a rat model to test skin survival, providing early support for the use of HBOT. McFarlane demonstrated the effectiveness of neovascularization in his study showing thick graft survival only in a group receiving HBOT. Skin flap studies by Nemiroff and by Zamboni have demonstrated markedly greater skin survival in the HBOT treated group, as did those of Rubin. Clinical studies have confirmed these findings, including those of Perrins, who showed a 50 percent improvement in graft area survival over controls, and a remarkable 400 percent increase in the number of treated patients with complete graft take. Bowersox’s review of 105 patients with hypoxic grafts or flaps further support the clinical efficacy. The work of Hill demonstrates that a graft can be a composite of different tissues, of large size, and still be directly grafted with success.
Skin grafts, by their process, are hypoxic. Grafts are used to cover areas that are devoid of skin due to trauma or disease, so the recipient site is ischemic, and it is this site that will provide the support for the graft. The skin graft is cut from all of its blood supply. Next, it is placed upon the compromised tissue base, where it must initially rely completely upon oxygen that diffuses from the base, and later upon rapid angiogenesis from the base and wound margins so that the graft’s vascular structure can be reconstructed. Skin flaps must overcome similar problems due to the stretching and twisting of their vascular tree. Hyperbaric oxygen therapy ameliorates the hypoxia, post-operative swelling, and ischemia of grafts and flaps. HBOT provides high concentrations of oxygen to the graft bed so that more oxygen can diffuse into the graft to sustain it during an ischemic period. The anti-edema effect of HBOT improves tissue oxygenation by reducing the distance oxygen must diffuse, and by improving perfusion (Nylander, 1985). Neovascularization is enhanced by the steepening of the tissue oxygen gradient by HBOT (Knighton, Gottrup, 1981). Finally, as the neovascularization progresses, HBOT reduces the “no reflow” phenomenon (Zamboni, 1993).
Animal and human studies support the use of HBOT in skin grafts and flaps. Hunt and Van Winkle demonstrated that a minimum oxygen value of 30 mm Hg was required for cellular function, with Hunt and Pai showing that an optimal PO2 for healing is in the 50 to 100 mm Hg range. Sheffield documented that many wounds do not reach this critical range, so healing is impaired. He further showed that HBOT can provide oxygen levels of 1,000 mm Hg or more. Gruber et al., demonstrated that elevated PO2 from HBOT was found in the skin graft itself. In their randomized, prospective animal study, Nemiroff et al., showed greatly increased survival of ischemic flaps that were treated with HBOT (p<0.05). Collins et al., demonstrated enhanced survival of rat skin flaps with hyperbaric oxygen (p<0.01) in their prospective randomized study, as did McFarlane in a rat skin graft model. Zamboni et al., showed markedly reduced skin necrosis in the rat model, with 5 percent necrosis in the HBOT group, compared to 28 percent in controls (p<0.0005). Kaelin et al., extended such results to free flaps as well, with a 66 percent improvement in survival (p<0.01). Human clinical experience has also well documented the benefits of HBOT. In his prospective, randomized, controlled study, Perrin found marked improvement in the percentage of total graft take, with 64 percent of the HBOT group having complete survival, compared to only 17 percent of controls (p<0.01). Similar improvements were found for overall percentage of graft take, and for overall graft success (p<0.01). In their large clinical study, Bowersox et al., showed the effectiveness of HBOT on skin grafts, as has Perrins. Hill et al., have shown that large composite grafts, including entire ears, can be grafted using adjunctive HBOT. Reedy et al., have shown that the use of HBOT markedly increases the healing of wound flaps in patients following radical vulvectomy (p=0.035). Zamboni has shown the effectiveness of HBOT in grafting and in reimplantation of limbs, with a salvage rate of 75 percent for the HBOT group (n=16), compared to 46 percent (n=13) for the controls, with 100 percent HBOT salvage when the patient is treated within 72 hours post-operatively.
Upon review of the medical literature, the authors conclude that the use of HBOT for the preparation of a base for skin grafting and the preservation of compromised skin grafts has been well documented as effective.
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