When the burn wound is deep partial thickness (Fig. 126.1A), it may be possible to preserve some dermis by performing tangential excision. This provides an excellent bed for skin grafting while maintaining the underlying structure of the skin. It is absolutely essential that a clean viable bed be achieved. Classically, this is done by observing punctate bleeding from the excision bed, and this may result in considerable blood loss. Tangential excision is commonly limited to small cosmetically or functionally sensitive areas such as hands and fingers.

Perform tangential excision with a handheld dermatome such as a Weck knife. Guards are available for various thicknesses. Place the knife at the farthest margin of the patch to be excised. Rapidly move it from side to side, producing a sawing motion that enables the knife to cut a slab of dead tissue off with minimal force. Progress down through the area to be excised (Fig. 126.1B). Generally multiple passes are required to excise the entire area. The goal is not to excise the full depth of the burned area in the first pass (although this may occasionally happen), but rather to sequentially excise all of the burned tissue in several layers for maximal control.

Wipe the dead tissue off the knife and insert a new blade when the one you are using becomes dull.

Carefully progress, excising layer by layer until clean, viable, bleeding tissue is seen. All burned and devitalized areas must be removed to provide a good bed for skin graft. If you are using a tourniquet to limit blood loss, you will not see bleeding but should note clean glistening moist white tissue. More practice is required to recognize the correct depth of excision in this situation.

Obtain hemostasis with pressure and electrocautery. Place a moist laparotomy pad over the prepared recipient site while you obtain the graft (see Figure 126.4).

The epidermis is the portion of skin superficial to the basement membrane. This layer is the primary barrier against evaporative water loss and injury from the outside world. All burns injure this layer. The epidermis is avascular and is divided into five layers. From superficial to deep these are stratum corneum (the outermost layer of dead cells), stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale (the layer in which new cells are formed). Cells in the stratum basale divide, producing new epidermal cells that are pushed upward through the various layers to eventually die and form the stratum corneum. The dead cells of the stratum corneum are shed in approximately 2 weeks. In addition to the epithelial cells, the epidermis contains Langerhans cells (a crucial part of the immune system), melanocytes, and Merkel cells.

The dermis contains collagen and elastin as well as reticular fibers. It is divided into two layers: The upper papillary layer and the lower reticular layer. The dermis provides structural support for the epidermis. It contains hair follicles and their associated erector pili muscles. Numerous blood vessels and nerves traverse this layer. Glands (sebaceous, apocrine, and eccrine) are found here. Regeneration of deep partial thickness burns occurs by re-epithelialization from these deep structures. Specialized nerve cells that sense pressure and touch are also located here. Burn injuries that completely destroy this layer are classified as full-thickness (or third degree). Because the nerve injuries are destroyed, these full-thickness burned areas are anesthetic and may be surprisingly painless.