Autolytic Debridement

Autolytic debridement (26-33) occurs spontaneously to a varying extent in all wounds and is because of macrophages and endogenous proteolytic enzymes, "which liquefy and spontaneously separate necrotic tissue and eschar from healthy tissue" (10).

The spontaneous autolytic debridement can be enhanced by moist dressings that create and maintain a moist environment capable of stimulating macrophages and endogenous pro-teolytic enzymes to carry out their action and promote tissue granulation.

The favorable effects of moist environment on wound healing were first described by Winter (34) on a swine experimental model and was repeated by Hinnman and Maibach (35) in humans.

They described a higher epithelialization rate for wounds occluded by a polyethylene film when compared with wounds freely exposed to air. Histological studies demonstrated that the dry environment causes further tissue necrosis probably because of the dehydration itself; it was also shown that epithelial cells can move faster in a moist environment when compared with a dry one (36). Subsequently, it was reported that a moist environment as created by semiocclu-sive or occlusive dressings does not induce bacterial growth or an increase in the infection rate but that, on the contrary, resulted in prevention by this peculiar condition (37).

Hydrogels are formed by insoluble polymers with a high concentration of water (up to 90%); sometimes they contain glycerine to delay water release; they can be manufactured as amorphous gel or compress and are the first choice in case of necrotic tissue or dry fibrin slough; they are unsuitable for wounds with high level of exudate and need to be changed within 24 to 72 hours. The amorphous gel needs a secondary dressing (e.g., film or hydrocolloids) in order to be maintained on the ulcer bed and avoid adsorption by the padding material of the bandage.

Hydrocolloids contain carboxymethylcellulose, other polysaccharides, pectin, and noncy-totoxic adhesives. Their outer layer is formed by a waterproof polyurethane sheet that makes the dressing occlusive; they gel on contact with wound exudate and create a moist environment. When the adsorbing capacity of the dressing is lost it tends to detach and must be changed (usually after 24 to 48 hours in ulcers stuck in the inflammatory phase) (Fig. 1). They are indicated for mild to moderately exudating wounds. The hydrocolloids can also be used over granulation tissue and in the epithelialization phase. In this case, they can be changed even after one week depending on the exudate amount. Rarely, they cause allergic contact dermatitis (29).

Film dressings are formed by polyethylene and polyurethane with acrylic adhesive; they are permeable to water vapor and oxygen but impermeable to water and micro-organisms and

FIGURE 1

Large vasculitic ulcer: (A) covered by fibrin slough; (B) dressed with hydrocolloid; (C) the same after two days and (D) after eight days and four dressings. The ulcer bed is now debrided and is in the granulation phase.

FIGURE 1

Large vasculitic ulcer: (A) covered by fibrin slough; (B) dressed with hydrocolloid; (C) the same after two days and (D) after eight days and four dressings. The ulcer bed is now debrided and is in the granulation phase.

do not have any absorbing ability. Their indication is restricted at the later stages of wound healing when there is not abundant exudate or as secondary dressing to keep other dressings (e.g., hydrogel) in contact with the wounds or to help in creating a moist environment.

Calcium alginate is formed by fibers of alginate (derived from brown seaweed) and tied together by calcium. They can have manuronic acid content (which gives a high gelling capacity) or galuronic acid content (which gives good fiber integrity). Calcium alginate exchanges calcium with the sodium ion in the exudate; calcium alginate is converted into sodium alginate causing the alginate to form a gel and promoting moist environment. The alginate gel adheres to the wound bed, trapping exudate and bacteria within its structure and promoting their removal during dressing change. The calcium donated to the wound fluid promotes a hemo-static effect. Calcium alginate is ideal in stimulating granulation tissue in exudative and infected wounds even when indented, undermined, or cavitary. Finally, the alginate gel can be removed without considerable trauma, allowing a poorly painful dressing change (Fig. 2).

Hydrofibers consist of sodium carboxymethylcellulose; they are able to absorb and lock considerable amount of exudate and bacteria into a cohesive gel and reduce the lateral wicking; they are indicated in moderate to heavily exudating wounds even if infected. Compared with alginate (31) they showed a longer wear time, a lower cost, better ease in application and removal but no statistical difference in numbers healed.

Polyacrylate is a new multilayered dressing pad containing superabsorbent polyacrylate activated with an appropriate volume of Ringer's solution. The polyacrylate has a greater affinity for protein-containing wound exudate than for salt-containing solutions (Ringer's solution); the wound exudate displaces the Ringer's solution from the superabsorbent pad. The Ringer's solution, in its turn, is given off continuously to the wound bed over hours (12 or 24 hours depending on the type of dressing used—if standard 12 hours or extended 24 hours). This permanent inflow of Ringer's solution softens and loosens necrotic tissue and, at the same time, superabsorbent poly-acrylate absorbs and entraps bacteria, detritus, and toxins.

TenderWet®, therefore, can be used in infected and noninfected ulcers. According to our data (32), TenderWet 24 is capable of absorbing large amounts of exudate and can effectively and

FIGURE 2

Large vasculitic ulcer: (A) covered by fibrin slough; (B) dressed with calcium alginate; (C) the same after four days and (D) after nine days and four dressings. The ulcer bed is now debrided and is in the granulation phase. (See color insert.)

quickly get rid of necrotic tissue, fibrin, and debris, promoting the appearance of the granulation tissue in a few days; it also has a noticeable effect in decreasing dramatically the bacterial burden, sometimes just after the first dressing, absorbing the bacteria and binding them inside the polyacrylate pad (Fig. 3).

The dressing is fairly atraumatic and slightly painful at removal if it is not moistened plentifully with saline solution; when removed, the ulcer bed is "clean" and further wound cleansing necessary with the other kinds of dressings is not required. This substantially contributes to the good compliance of the dressing as the mechanical ulcer bed cleansing during the change of dressing is usually the most painful event of all the procedures. When properly placed, Tender-Wet is well tolerated and does not cause any particular complication.

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