Which of the following statement(s) is/are true concerning techniques of burn excision, and temporary and definitive wound closure?

a. Techniques to conserve blood include subeschar injection of dilute epinephrine solution, exsanguination of the extremity and inflation of a pneumatic tourniquet

b. Fresh or cryopreserved human allograft is usually rejected within 2 to 4 weeks

A common argument against the policy of early burn wound excision is the prodigious blood loss which has been associated with these procedures. However, modern blood conserving practices as well as earlier excision of wounds have diminished this concern. Tangential excision of the torso, neck and head are done after subeschar injection of dilute epinephrine solutions. Tangential excisions of the extremities are done after exsanguination and inflation of a pneumatic tourniquet. Once necrotic eschar is excised to a bed of viable tissue, immediate biologic closure is mandatory. Ideally, immediate autografting is performed. When donor sites are insufficient for this purpose, a temporary biologic cover must be chosen while awaiting healing of donor sites for further use. Such covers should prevent desiccation and provide a vapor and bacterial barrier over the excised wound. Fresh or cryopreserved human allograft is most appropriate for this use. Once placed on a viable wound bed, it will vascularize and provide physiologic wound closure until rejected 2 to 4 weeks later at which time or before, it is replaced with reharvested autograft. A second common use for biologic dressings is a physiologic cover for selected clean superficial wounds as they epithelialize, which minimizes the pain associated with open partial thickness burns. Allograft, screened for malignant and infectious diseases, a precarious resource, is however, not commonly used as a biologic dressing in these circumstances. For this purpose, reconstituted porcine xenograft should be used.