Skin grafts - Biomaterials for Treating Skin Loss - page 65

and, periodically, underlying fluid collections must be expressed by rolling the
graft with a cotton-tipped applicator. Any blebs of blood or serous fluid that form
beneath the graft should be incised with a No. 11 scalpel and drained expeditiously.
Use of fibrin sealant at the time of grafting may decrease the incidence of seroma
or hematoma formation under sheet grafts (Gibran et al ., 2007; Mittermayr et al .,
2006; Greenhalgh et al ., 1999; Saltz et al ., 1989).
Skin grafts require a vascular bed and will seldom engraft on exposed bone,
cartilage or tendon without the presence of periosteum, perichondrium or paratenon,
respectively. In addition, close contact between the skin graft and its recipient bed
is crucial for revascularization; thus, hematomas and seromas under the skin graft
or sheer stress will compromise its survival. It is crucial to ensure the wound to be
grafted has a vascularized bed free of infection or malignant disease and hemostasis
has been achieved (Gingrass et al ., 1975). Finally, the thicker the graft, the more
well-vascularized the bed must be to support engraftment.
5.3.3 Process of successful engraftment
The success of skin grafting or 'skin graft take', depends on the ability of the graft
to receive nutrients and, subsequently, the ingrowth of vascular elements from the
recipient bed. First and foremost, wound beds need to be adequately vascularized
and free from debris and infection. This process of successful skin graft acceptance
occurs in three stages. The first stage, lasting over approximately 24-48 hours,
depends on plasmatic imbibition (Converse et al ., 1969). Plasma leaks from
recipient venules into the space between the graft and the host bed (Kikuchi and
Omori, 1970). Fibrinogen, within the extravasated plasma, settles and forms a
glue-like substance that anchors the graft to the bed. Nutrient absorption into the
graft occurs by passive capillary action from the recipient bed. Once in contact
with the recipient site, the graft becomes edematous and increases in size up to 30%
(Converse et al ., 1957). The energy demands of the graft fall as metabolism occurs
via anaerobic respiration (Hira and Tajima, 1992).
The second stage requires the cut ends of the recipient and donor end capillaries
to align and form microscopic anastomoses - a process known as inosculation first
coined by Thiersch in 1874 (Thiersch, 1874). This process begins immediately
after graft placement, and vascularization occurs by four days (Davis and Traut,
1925). Most reports indicate that vascularization becomes normal by four weeks
(Converse and Rapaport, 1956; Haller and Billingham, 1967; Rolle et al ., 1959).
In contrast, flow within allograft skin improves until day 6 then halts by day 9
owing to rejection (Scothorne and Mc, 1953; Kamrin, 1961; Egdahl et al ., 1957).
The final phase is marked by revascularization of the graft after capillary
alignment. Multiple theories exist to explain this process. One prominent theory
proposed by many German surgeons in the late 1800s describes how the original
graft vasculature degenerates. Subsequently, host endothelial cells and capillary
buds invade the graft via the acellular graft basal lamina, which provides a conduit