Clinical studies

Although animal studies considering the reported evidences on compromised grafts and flaps confer a high degree of validity, relevant human studies for HBO as adjunct therapy are essential to enroll it in the therapeutic armamentarium.

In 1966 Perrins reported the use of HBO to enhance flap survival reducing the failure rate in a series cases and next year he presented a controlled study106 of HBO effect on skin split grafts. The protocol included 48 patients randomly assigned to a control and HBO treated group. The graft survival rate in the HBO group was 64% versus 17% in the control, statistically important, although the low percentage in untreated patients was not explained.

Greenwood et al.107 in 1973, having already experience with HBO use in irradiated rats on skin flaps78, studied the action of HBO on healing of compromised wounds in irradiated patients with laryngectomy. They concluded that HBO enhanced the restoration process.

Wilkox et al.108 in 1976 conducted a study with thirty-eight osteotomy patients treated with HBO to determine clinically its effect on the healing acceleration. Data accumulated from this clinical investigation indicated that HBO augments clinical healing subsequent to osteotomy procedures.

Perrins109 in 1983 reported that in graft donor site, when a secondary hypoxia is present, HBO enhances the healing rate e.g. in burns, making grafts transfer possible in a shorter period than expected. HBO use in normal conditions, concerning graft bed healing, is neither necessary nor recommended.

In 1986 Bowersox et al.110 in a retrospective analysis reviewed a series of 105 patients with ischemic flaps and grafts, where HBO had been used as adjunct therapy. In 90% of the grafted patients and in 63% in those with flaps, conditions appropriate for failure of transferred tissues were recognized. HBO contributed to avoid creation of "compromised tissues", as the survival rate in grafts was up to 91% and the relevant in flaps up to 89%.

Davis et al.111 in 1987 reported a series of 4 patients suffering from pyoderma gangrenosum wounds, unhealed for many years even after intensive treatment with all therapeutic modalities (debridement, steroids, antibiotics and multiple skin grafts). Authors used HBO combined with skin grafting and all patients healed with a follow-up period of 4-6 years, free of recurrences. Prior of this report, in the presence of pyoderma gangrenosum, graft prognosis was unfavorable.

Ueda et al.112 in 1987 in a retrospective analysis in a series of 26 patients with oral deformations, after removal of mouth or tongue cancers, reported that the developed compromised flaps achieved a 95-100% recovery.

In 1993 Waterhouse et al.36 in a clinical controlled retrospective review described the effect of HBO in compromised free tissue transfer and replantation. Patient inclusion criterion was the presence of 6 hrs of primary or any secondary ischemia. Salvage in the HBO group (16 cases) was 75% versus 46% in the control group (13 cases). Timing of HBO application proved mostly significant for salvage rate, being 100% when free flaps and replants were treated within 24 hrs after the injury. On the contrary, when HBO was performed later than 72 hrs, failure occurred in all transferred tissues. Thus, the author proposes that HBO therapy should be initiated as soon as possible in order to avoid a post injury prolonged period of ischemia leading to irreversible lesions.

Marx and Ames113 in 1982 proposed the efficacy of HBO in radiation injuries. Reconstructions of the mandible or maxilla using a newly defined and specific hyperbaric oxygen protocol were combined with grafts in irradiated tissue, into scarred and deficient tissue beds. Eleven of 12 grafts in irradiated tissue met six rigid criteria for a 91.6% rate of success. Neovascularity and neocellularity were demonstrated histologically (by human biopsy specimens) and were valid for the excellent results of reconstruction in irradiated and/or deficient tissue beds. Davis et al114 in

1981 had also presented a study proposing HBO as a new adjunct in the management of radiation necrosis with surgery and antibiotics. Fifteen of the 16 cases of soft-tissue radionecrosis of the head and neck were successfully managed.

Reconstructive attempts in studies by Marx et al.115' 116 as also by others117 have demonstrated extensively the close relationship of HBO to bone graft healing.

For over half a century HBO application in radio-injuries to treat late complications is widespread in literature through retrospective trials and case reports' even if most of the studies results were more than encouraging.

In 1994 Marx118 reported that in a series of 104 patients with hemimandibular reconstruction, success percentage was up to 92% in the HBO group with 52 patients versus 65% in the controlled group. The author links the success to induced angiogenesis and fibroblasia by HBO, implying that live bone cell transplantation into HBO treated tissue produces a greater survival of cellular elements and greater bone formation.

Furthermore, as soft tissues are also influenced by radiation injury, microvascular free flaps were introduced in the field of osteoradionecrotic lesions in a combined effort to restore in parallel soft tissues and bones defects. The most often involved areas are in the neck and head, followed by the pelvic region.

Although free flaps carry their own vascular support, the prognosis for a normal rate adherence with the radio -injured underlying tissue is not always favorable. This possibility of poor outcome establishes HBO use an important supportive procedure as adjunct therapy.

Marx et al.118 had accomplished a randomized prospective study in irradiated patients, dealing with three aspects of the problems related to soft tissue flaps and wound healing:

a) delayed wound healing b) minor or major wound dehiscence and c) infection.

106 irradiated patients, with a dose greater than 64Gy, participated in two groups of 80 each, one group with HBO therapy and one as control. All patients were submitted to a flap or a major tissue surgery. In the HBO group the results were:

a) wound healing delay only 11 % versus 55 % in the non treated group b) "minor" rate of wound dehiscence (defined as one that healed in 3 weeks) of 7.5 % versus 15 % in the control group and "major" (unhealed in 3 weeks or requiring secondary surgery or HBO) of 3.5 % versus 33 % respectively c) "minor" rate of wound infection (defined as the one responding to antibiotics, culture specific and local irrigation) of 3.5 % versus 7.5 % in the control group and "major" rate (surgery debridement in addition to minor) of 2.5 % versus 16 % respectively.

The study, according to the author, clearly confirms the value of HBO performed protocol to reduce additional surgeries, disability and total cost of car.

In summarizing studies review, several articles have been published in the medical literature concerning the experienced use of HBO to improve viability in "uncertain" transferred tissues. The acquired results have shown that a beneficial effect was evident in most of the experimental and clinical studies.

Inclusion or acceptance of any new therapeutic approach is related to "evidence based medicine", meaning properly organized protocols through double-blind controlled randomized studies, or strong evidence of beneficial action.

Human flap variety techniques is similar to the one in animal models, making protocol standardization design almost impossible, thus comparable analysis of the results is not practical or feasible. Furthermore in light of the last controlled animal studies, patient inclusion in the non-treated groups may raise ethical matter.

Rapid strides in modern plastic surgery on transferred tissues imposes the need for further research of HBO action in the survival of "compromised" grafts and flaps.

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