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Revascularization surgery in infected fields - an issue yet to be solved
(Portuguese PDF version)

A. Dinis da Gama *

* Clínica Universitária de Cirurgia Vascular, Hospital de Santa Maria, Lisboa, Portugal.

J Vasc Br 2005;4(2):116-9

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The revascularization surgery performed in infected fields, namely in circumstances of aorto-iliac prosthetic infection or infectious aneurysms (inappropriately called "mycotic"), persists as one of the major problems of the contemporaneous vascular surgery, to which there are still no totally satisfactory or consensual solutions. As a consequence, several alternatives have been provided, all of which offer advantages and inconveniences that deserve to be analyzed and discussed.

The surgical treatment is essentially based on the complete excision of the prosthesis or infected aneurysms, almost always followed by a revascularization procedure, which can have two completely distinct aspects: the extra-anatomical revascularization and the local or in situ revascularization.

For several authors, the extra-anatomical revascularization, that is, the axillary-bifemoral bypass represents the preferential method,^1,2 although two significant limitations are attributed to it: the lower durability of grafts in terms of permeability levels, when compared to the conventional aortic surgery, and the specific complications that follow, namely infections and periprosthetic seromas, whose real etiology remains unknown. Besides these facts, it is essential to add the complications that may result from the infrarenal abdominal aorta ligature and the formation of an aortic stump, which may develop at medium- or long-term, consisting of aneurysmatic dilatations, dehiscences, and ruptures that are often severe and fatal.³

In situ revascularization procedures, on their turn, are divided into two chapters, according to the nature of the replacement material used: prosthetic replacement and biologic replacement.

The prosthetic replacement, made of polyester fiber or PTFE, presents the risk of reproducing the infection, due to its known vulnerability, with all the severe inconveniences which may derive from that. That is the reason why antibiotics, such as rifampicin,^4-6 or antiseptics, such as silver salts⁷ are bound to the prostheses. Patients should be judiciously selected for this type of revascularization, and one of the factors to be taken into consideration is the virulence of the bacterial agent, being usually contraindicated in case of highly aggressive varieties, such as the pseudomonas or the MRSA staphylococcus, given the risk of infection recurrence.⁶ Although very satisfactory results have been obtained in the animal experimentation related to the efficiency of antibiotic-impregnated prostheses,⁸ the truth is that clinical series that may certify the validity of the method under these circumstance are rare.

Biologic replacement which can be used in this context are the arterial autografts, venous autografts, and cryopreserved arterial allografts, which represent the object of a study by Zhou et al.,⁹ presented in this issue of the journal.

Starting with the arterial autografts, the experience reported in the literature is quite limited. The autologous superficial femoral artery has already been used in the past, but only in circumstances in which it was occluded, being necessary to perform its further reopening by endarterectomy with eversion, in order to obtain an adequate conduit for the revascularization procedure.¹⁰

The use of the permeable superficial femoral artery was recently described by da Gama et al.,¹¹ in very particular circumstances of aortic prosthetic infection. The graft proved to be extremely successful, and the results at medium-term showed a high quality biologic behavior. On the other hand, there were no significant complications in the donor limb circulation. Although in circumstances that are difficult to reproduce, it is an alternative that can be taken into consideration in the range of technical solutions related to the revascularization surgery in infected fields.

The autologous internal saphenous veins have also been tested in cases of prosthetic infection by Ehrenfeld et al.¹⁰ and Lorentzen & Nielsen.¹² Nevertheless, as Quiñones-Baldrich & Gelabert¹³ could show, the permeability of grafts was much dependent on the original diameter of the veins, being frequent the occurrence of focal stenosis in the small-caliber veins, due to intimal fibroplasia, which anticipated its occlusion, or to the need for multiple surgical repairs.

To overcome this inconvenience, Clagett et al., in 1993,¹⁴ decided to use the autologous superficial femoral veins, which have a much larger diameter and are more compatible to the abdominal aorta caliber, allowing the performance of congruent termino-terminal anastomosis and abolishing the problems caused by the aortic ligature and the formation of vulnerable and risky aortic stumps. Their good experience, which was progressively extended through the years^15,16 and further corroborated by other authors,¹⁷ allowed to recognize the superficial femoral veins as an excellent replacement, resistant to infections and with a biologic behavior free from complications, namely occlusions, dilatations or aneurysmatic degenerations at medium- and long-term. These authors report the good tolerance of patients facing the superficial femoral veins excision and the potential hemodynamic alterations that could occur in the venous flow of the donor lower limbs. In most cases, a clinical expression was not verified.¹⁸ One of the essential requirements for this to occur is the need of scrupulously respecting the limits and extension of the venous segment to be excised, which must not go beyond the popliteal vein, distally, and the confluence with the deep femoral vein, proximally.¹⁸

However, it must still be demonstrated the resistance of femoral veins against infections by aggressive and particularly virulent germs, such as the case of those previously mentioned (pseudomonas and MRSA staphylococcus).

Finally, cryopreserved or cryoconserved arterial allografts have been particularly used in Europe, mainly by Kieffer et al.,^19,20 and their greatest advantages lie in the fact that they are easily available, allowing the creation of real "artery banks". They are also more resistant to infections than the prosthetic replacement,²¹ therefore they can be implanted in infected fields, like Zhou et al.⁹ did.

The history of the use of arterial allografts is mingled with the early reconstructive vascular surgery. Once called homografts (cadaveric), they were initially used by Gross et al., in 1948,²² for the surgical repair of the aortic coarctation, followed by Oudot, in 1951,²³ for the treatment of the terminal aortic obstruction, by Dubost et al.,²⁴ in the same year, for the replacement of the abdominal aortic aneurysm, and by DeBakey & Cooley, in 1953,²⁵ for the treatment of the thoracic aortic aneurysm. Its biologic behavior was exhaustively studied by Szilagyi et al.²⁶ At long-term (from 5 to 15 years after implantation), a high incidence of clinical complications was observed, including occlusions, ruptures, parietal calcifications, and aneurysms, as a consequence of a process of irreversible degeneration that affected the graft. For that reason, homografts were excluded from the clinical practice and replaced by the prosthetic replacement, which have played a relevant role in the reconstructive vascular surgery over the past decades.

Homografts have been recently resuscitated due to progresses in transplantation and organ donation, as well as in the cryopreservation of tissues, this time called "allografts", and their privileged field of action has been, as previously mentioned, the revascularization surgery in infected fields. Against expectations, the experience gathered by several authors and researchers shows that the biologic behavior of allografts is not much different from the one described by Szilagyi et al.^20,27-32 Similarly, at medium- and long-term, the occurrence of the graft degeneration is verified, essentially by the disappearance of structural and cellular elements that form the tunica media of the wall, which contributes to its fragility and consequent complications showed in the clinical practice. Some attempts of explaining the phenomenon have been made, such as the interference of a possible phenomenon of chronic immunological rejection,^33,34 or pure mechanic failure.³⁵ We have formulated a very seducing hypothesis,³² based on clinical and experimental data, which consists of the development of a "degenerative ischemic mediopathy", as a consequence of the functional exclusion of the vascularization of the graft wall, due to failure of its nutritional networks of "vasa vasorum", which has a definite and irremediable character.

Whatever is the real explanation for the phenomenon, the reality is that cryopreserved arterial allografts have been reducing their application field, due to a limited duration of its viability, at medium- and long-term, a fact which the experience of Wei Zhou et al.⁹ could not demonstrate because of the short follow-up period comprehended by their study (mean of 8.3 months). Nevertheless, this reality will not obligatorily avoid it as a therapeutic alternative for the revascularization in infected fields. They are still particularly useful in the acute stage of the infectious process, which, once started, may give place to the prosthetic replacement that has a known durability. This is justified especially for young individuals, who hope to have their lives prolonged.

We are sure that this is the real current indication of cryopreserved arterial allografts for the revascularization surgery in infected fields: to serve as bridge in the most critical stage of the infectious process, until favorable and indispensable conditions are obtained for a safer and long-lasting solution, which is still currently the prosthetic replacement.

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