After 1960, apart from conventional closed dressing techniques, moist wound dressings and negative pressure dressings are the most commonly discussed in the literature.
The author designed the Limited Access Dressing (LAD) in an attempt to combine the advantages of both moist wound healing and negative pressure dressings.The design has notable advantages, while avoiding some major disadvantages such as an inaccessible, offensive smelling wound environment, and relatively high treatment costs.
Moist Wound Healing
It has been claimed that occlusive dressings promote rapid wound healing by preventing dehydration and scab formation, facilitating debridement, minimizing inflammation, reducing pain, increasing the rate of epithelialization, and diminishing scarring.1 However, there is concern that a moist environment may lead to bacterial proliferation and wound infection.2–4 Moistwound healing achieved by occlusive hydrocolloid produces offensive-smelling exudates and has raised some doubt about its effect on bacterial flora, specifically anaerobes.5,6
In 1962, moist wound healing was first described in an experimental wound7 and later in a human.8 An occlusive dressing that traps moisture on intact skin can produce an explosive proliferation of bacteria.9,10 Occlusive hydrocolloids are impermeable to water and the colloid gel, formed by absorption of exudate, produces an absorption gradient that removes the toxic components of the wound exudate that the cellular and bacterial destruction produce.11 The bad odor that is produced has been explained as a result of either gelatin breakdown in the colloid gel6 or anaerobic infection.6,12,13
Increasing evidence shows that the presence of many and varied bacterial species in chronic wounds does not adversely affect healing.14–19 The need for routine bacteriological culture swabs does not seem to be a necessity in chronic leg ulcers.20 This would result in considerable cost savings,and would avoid unnecessary use of antibiotics20 and toxic chemicals that may delay wound healing.21
Negative Pressure Wound Dressing
The vacuum sealing techniques (VST) were first described by Argenta et al22 and Fleischmann et al.23 Others24–27 have used VST for the treatment of acute traumatic soft tissue defects, soft tissue defects complicated by exposed bone and/or implants, and skin graft and flap resurfacing.The optimal topical negative pressure (TNP) regimen has not yet been established.
Nakayama et al28 have used negative pressure dressings on free skin grafts with an adhesive drape and a disposable suction drain. This method applies constant pressure on the graft and allows for easy inspection of possible hematomas and similar findings have been reported.29–32
Infected groin wounds following lymph node dissection and groin lymphorrhea have been effectively treated by negative pressure dressing.33,34
Limited Access Dressing (LAD): The Concept and Applications
How is LAD a combination of moist healing and negative pressure dressing? The Limited Access Dressing is a combination of intermittent negative pressure (for 30 minutes) and a moist wound dressing (for 31⁄2 hours without negative pressure) that is covered with a transparent polythene material (a total of 3 hours moist dressing and 21 hours negative pressure dressing in a 24- hour period). Negative pressure (up to -30 mmHg) is applied through tubing connected to a suction machine that is then placed under a polythene wound cover.
LAD designs. The material that contacts the wound LAD is classified into 2 groups:
A. Hydrocolloid material contacts the wound (LAD I, Figure 1)
B. Polythene sheet contacts the wound (LAD IB and LAD II, Figure 2)
Some may be skeptical as to whether a hydrocolloid material encountering the wound or negative pressure (LAD I) makes a difference. Liquefied hydrocolloid materials blocking the tube, and poor wound floor visibilityfor the initial few days until the suction removes any liquefied material, are two additional problems.
To avoid doubts and problems associated with LAD I, in LAD IB (Figure 2) a sterile polythene sheet separates the wound along with tubes from hydrocolloid and in the Hydrocoll® (Hartmann, Heidenheim, Germany) a central hole was made to improve visibility. LAD I and LAD IB was used for smaller wounds (up to 10 cm x 10 cm given that the maximum size of Hydrocoll was 15 cm x 15 cm).
In LAD II (Figure 3) wounds are covered with larger polythene sheets, polythene tubes, and polythene bags after placing tubes (as in other LAD designs) and when sealing is achieved with pieces of Hydrocoll and the adhesive polyurethane film (OpSite™, Smith & Nephew, Largo, Fla).
If required in critically ill patients, after taking out intravenous and other lines through the LAD polythene bag that covers the extremities, the puncture site may be sealed effectively.
How much intra-LAD negative pressure is effective? There is a general belief among most physiologists that true interstitial fluid pressure in loose subcutaneous tissue is slightly less than atmospheric pressure (average value of this pressure is negative in relation to atmospheric pressure and is approximately -3 mmHg).35
When the skin cover is absent in wounds,the pressure will rise to 0 mmHg (ie, equal to atmospheric pressure). These increases in interstitial tissue pressure from -3 mmHg to 0 mmHg will also cause the lymph flow to increase 20-fold35 and the re-absorption of fluid to increase through capillaries. Hence, the chances bacterial invasion and absorption of chemicals (toxins) through venules and lymphatics increases when edema increases the interstitial tissue pressure or produces an open wound that is not sutured.
If the interstitial tissue pressure is slightly more negative than -6 mmHg, the lymph flow is slight 35 and consequently, the absorption of interstitial fluid will be negligible. As a result, the risk of sepsis due to bacterial invasion and the risk of systemic inflammation syndrome (SIRS) due to absorption of pro inflammatory cytokines will reduce considerably at -6 mmHg.
Surgeons generally believe that after wounding the wound remains contaminated for 6–8 hours, after which bacterial invasion occurs. If negative pressure (more than -30 mmHg) is applied every 31⁄2 hours for 30 minutes chances of invasive wound sepsis and SIRS will be reduced considerably—the author determined this schedule by a trial and error method and through daily observation of changes in wound granulation appearance after applying the LAD in more than 1000 cases while generating a maximum -30 mmHg negative pressure through the suction machine.This level of pressure (-30 mmHg) not only appears to be safe for most of the tissues, but also produces a desirable negative pressure effect even if slight leakage occurs. Magnitude of negative pressure is directly proportional to the pain and discomfort produced.
Leech effect of LAD. The intermittent negative pressure (cycle of 30 minutes suction and 4 hours rest) produces a leech effect.The leech effect is beneficial in the following ways:
1. Intermittent negative pressure of LAD can possibly retain local, beneficial effects of cytokines (inflammation, fibroplasia) during the rest period, but drains it out during the suction period; thereby, the leech effect removes the deleterious systemic effects of proinflammatory cytokines (SIRS). It also most likely removes chemicals producing progressive capillary thrombosis and, hence, the chances of progressive necrosis requiring repeated debridement after a crush injury, for example, is reduced.
2. Intermittent negative pressure prevents bacterial invasion,35 removes cytokines, and toxins along with the wound secretions.
3. Intermittent negative pressure helps relieve venous congestion (like the leech effect) and increases tissue oxygenation.
Evidence in favor of leech effect:
Effect on renal failure. High concentrations of proinflammatory cytokines have been reported to correlate with the prognosis of sepsis and the development of multiorgan dysfunction syndrome.36 In critically ill patients with ARF, proinflammatory and anti-inflammatory cytokines are markedly elevated in the presence or absence of sepsis and associated with significant increase in the risk of death.36 A preliminary study (unpublished data) indicates that use of LAD dressing helps in recovery from ARF associated with wound sepsis- related SIRS. The following case reports support the evidence of the leech effect.
Case 1. A 21-year-old man, presented with raw areas on both lower limbs with bilateral ankle subluxation following a scooter accident (Figure 4). The patient’s hemogram, routine and microscopic urine examination, and renal function tests were all normal (blood urea 15 mg/dL, creatinine 0.9 mg/dL). He underwent wounddebridement in the emergency department and 3 days later was diagnosed with acute renal failure (blood urea 116 mg/dL, serum creatinine 3.0 mg/dL, and serum potassium 3.9 mEq/L). Limited Access Dressing II was applied and the same antibiotic and supportive treatment was continued. Blood urea and creatinine levels returned to normal levels (serum creatinine 1.3 mg/dL) over the course of the 6 days he was under observation by nephrologists (no further active interventions were taken in this period). Wound debridement was performed and a new LAD II was applied again after 15 days. Thirty-five days after the first LAD application, a splitthickness skin graft was applied.Subsequently,more than 98% graft take was seen on postoperative day 10.
Case 2. A 55-year-old man was admitted with acute renal failure after being bitten by a Viper snake on the top of his right foot 2 days prior.Venous Doppler showed compressed veins in the right lower limb caused by tense subcutaneous edema. No evidence of thrombosis was present. Ultrasound of the abdomen showed bilateral grade I renal parenchymal changes. At the time of admission the renal function test was abnormal (blood urea 90 mg/dL, serum creatinine 4.7 mg/dL, K+ 4.6 mEq/L).A subsequent renal function test showed a deteriorating trend that required hemodialysis.After 2 days of hemodialysis, debridement was performed. Following the 5 hemodialysis treatments in 8 days, the patient’s blood urea was 95 mg/dL, serum creatinine 5.3, and K+ 4.2 mEq/L. At this point treatment remained the same, and a LAD II was applied.After 5 days with the LAD, the serum creatinine level (without dialysis) was 4.7 mg/dL. His blood urea creatinine level slowly became normal (serum creatinine 1.3 mg/dL) in 26 days without dialysis. Split-thickness skin grafting was done after 42 days of LAD. Graft take of 100% was seen postoperative day 10. The patient was discharged 2 weeks thereafter.
Toxic symptoms. Toxic symptoms associated with gangrene are not observed when gangrenous tissue and part of the body is covered in LAD even for longer duration (more than a week, Figure 5). This perhaps is because the major part of the pro-inflammatory cytokines (TNF-α and IL-1) responsible for SIRS are removed along with oozing by negative suction. In addition, infection was effectively prevented by LAD suction; hence, bacterial endotoxins and various inflammatory mediators released in infected tissue remains under control.
Indications of LAD. To avoid infection in acute, subacute, or chronic wounds. LAD is used for postoperativewounds in immunocompromised patients or patients with diabetes, also as a temporary cover for exposed bare bone, cartilage, tendon, and joints.Abdominal wall reconstruction and intra-LAD tissue expansion adjacent to the wound (Figure 6) are additional uses. It is technically difficult to apply the LAD over the face and perineum.
The LAD may be applied after abscess drainage and after 7 to 10 days (before skin edges retract significantly). Secondary suturing over the suction drain may be done to promote faster healing and a better quality scar.
LAD wash. To avoid wound infection and to control bad odor, the surface bacteria can be removed by mechanical saline wash through the LAD tubes. This keeps the wound in a dependent position and avoids liquefaction of hydrocolloid material from water and any leaks.The physician may instill the antimicrobial solution of choice after the wash.
Intra-LAD physiotherapy. When the triad of edema, immobility, and inflammation coexist, a vicious cycle develops with each feeding off the other, resulting in rapid stiffening of uninjured joints and tendon adhesions.37 Generally, a favorable situation results if 2 of the 3 factors are controlled.Edema was not a problem in any of the presented cases due to the intermittent compression produced via the negative pressure combined with early intra-LAD mobilization. Early intra-LAD physiotherapy helps minimize stiffness—the most common cause of persistent physical impairment in hand trauma cases.
LAD protocol for trauma: early wound isolation. LAD application over trauma areas reduces contamination and infection risk in acute wounds.A report (unpublished data) on wound infection studied wound swab cultures taken in the pre-LAD period and 7 days after LAD application.The results showed that in LAD I there was eradication of gram-negative infection in 98.74% (18/19 wounds), and in LAD II, eradication of gram-negative bacteria in 100% of cases.However, after 7 days new growth of gram-negative bacteria was seen in 50% of LAD I (14/28 wounds) and 57.14% of LAD II (12/21 wounds). Both LAD I (8 wounds) and LAD II (2 wounds) were effective in eradicating gram-positive bacteria in all cases and none of the wounds (LAD I, 0/28 wounds;LAD II, 0/21 wounds) showed new growth of gram-positive bacteria.
After LAD, elastic crepe bandages in cases of bleeding wounds (over extremities) and in cases of bone, joint, ligament, tendon, or nerve injuries appropriate splints may be applied.
Debridement and LAD. LAD is applied after thorough mechanical wash and surgical removal of dead tissue (Figure 7). After about 1 week (time determined by appearance of soft and relatively loose slough),if deemed necessary, the wound is debrided again. During debridement, slough is removed easily with minimal blood loss. In compound comminuted fracture cases, as much bone pieces as possible should be preserved to increase the chance of survival while the wound is under the LAD.
Complications. Applying a pressure bandage or continuous suction initially prevents intra-LAD hematoma. Once hematoma is formed it is gently broken with finger pressure under LAD,hydrogen peroxide (H2O2) wash and intermittent suction usually over 1 to 2 days assists in removing hematoma.Without vascular surgery in casesof complete arterial block LAD may fail to produce a desirable effect. In these cases, pressure exerted by tight LAD bag/tubes may produce ulceration over toes and other parts under the LAD. LAD is not effective if the target tissue is not exposed to negative pressure (ie, subcutaneous infection with intact skin). In these situations, 1 tube is inserted in deep-seated infection site before applying LAD.
LAD I application. After minimal wound debridement (under regional block/intravenous anesthesia/local anesthesia), a closed suction drain and 12 French feeding tubes are placed either over the skin surface or through a puncture wound.The surrounding skin is cleansed with ether and the wound is covered with Hydrocoll. As an additional measure to secure the LAD, an additional adhesive polyurethane film (OpSite) is used and if required, the Hydrocoll stitched to the skin around the wound with a 3–0 nonabsorbable monofilament suture.
LAD IB application. In LAD IB the wound is covered with a polythene sheet of suitable size after placement of the 2 tubes and is then covered with the larger size Hydrocoll. A central hole is cut in the Hydrocoll to increase visibility through polythene sheet, and the polyurethane film is applied as done in LAD I.
LAD II application. For LAD II either ethylene oxide sterilized polythene (0.15-mm thick) sheet/bags (presealed adult size bags for extremities) are used; or based on the size, shape, and wound site, customized bags or tubes can be sealed using a semiautomatic sealing machine and sterilized by immersion in 2.45% w/v glutaraldehyde solution for 20 minutes.
After placing 2 tubes (12–14 FR tubes with multiple holes), the wound is covered with a polythene sheet that is neither permeable to water vapor nor to bacteria, and is sealed with Hydrocoll (after cleaning the skin with ether). Additional adhesive polyurethane film (OpSite) was applied to cover and secure the position of the hydrocolloid and to create a watertight seal. Plaster slab immobilization was done in suitable cases. Three basic designs of the polythene cover were used in LAD II— bag, tubular, and patch design.
One LAD tube was attached to a suction drain bottle and through other tube intermittent suction (-30 mmHg) was applied for 30 minutes every 4 hours from an ordinary hospital suction machine capable of generating 300 mmHg of negative pressure. Minor leaks noted during application of suction were ignored. For instance, maintaining negative pressure > 30 mmHg was possible in spite of leak. For moderate leaks resealing was done (ie, maintaining negative pressure > 30 mmHg was possible after applying a pressure dressing at the site of sealing). If a major leak occurred and maintaining a negative pressure > 30 mmHg was not possible and wound secretion was noted just after the end of suction period in spite of resealing, the LAD was changed.
Also, the amount of leakage was monitored subjec-tively based on reduction in compression, compared to that at the time of application felt by the patient. Leakage amount was monitored objectively by the amount of force required to pull the folds of polythene away from the wound surface after negative pressure application.
Split-thickness skin grafts with the LAD were covered with a non-stick,polyolefin mesh that was sutured to normal skin to avoid accidental displacement of the graft under the LAD.The LAD was removed on postoperative day 10.Two layers of non-stick, polyolefin mesh covered donor areas in all cases with 14 French tubes between them, which were covered with an adhesive polyurethane film. In the postoperative period, LAD intermittent suction (30 minutes suction, 4 hours rest) was applied over the recipient and donor areas.
Thirty-nine cases of wounds that underwent splitthickness skin grafting that were covered with LAD II were performed (between July 2004 and March 2005) were studied.Wounds that were either not prepared by LAD II, in cases where the resurfacing was done with a skin flap, or skin grafting was not done under LAD II, were not studied.The case sheets of these patients were reviewed and personal data, diagnosis, treatment method, time taken to treat the wound or to get the desired effects and outcome were noted (time to appearance of healthy granulation tissue judged by color, amount of exudate, and amount of graft take by day 10 if grafted under LAD), and results were analyzed.
The age range was 3.5 months to 86 years (median 32 years) and male to female ratio was 4.57 to 1.Wound etiologies that were studied are shown in Table 1. Twentyfour of 39 wounds were located on lower extremities, 13 wounds on upper extremities, and the remaining 2 on the torso.Twelve cases had exposed avascular structures (bone , tendons , bone and joint , bone and tendon ). On average, wounds were 21.56 days old and required an average of 1.51 LADs (range 1–3) to prepare the wound properly for skin grafting.The average number of days required to prepare the wound under LAD was 17.05 days.
All 39 wounds were treated with one LAD application with 100% graft take. In one case graft take was 95% and required repeated LAD preparation for 10 days to achieve healthy granulation tissue and subsequent 100% graft take. On average, 1.03 LAD applications were required to cover wounds with a skin graft (range 1 to 2; median 1).
Twenty-four of 39 wounds were treated with conventional dressings for more than 7 days. In these cases, an average of 33.83 days, conventional dressing (range 7 to 120 days; median 22.5 days) could not achieve healthy granulation suitable for skin grafting.These wounds were switched to LAD wound preparation and took an average of 13.2 days (range 3 to 32 days; median 12 days) to develop granulation appropriate for grafting.The average number of LADs required to prepare these wounds was 1.46.
In 1975, hydrocolloid dressing was introduced to absorb exudates forming a moist gel on the surface of the wound.38 The moist gel maintains the moist and warm wound environment suitable for growth of the granulation tissue, controls wound infection, increases rate of epithelialization and reduces pain.
Negative pressure dressing using an adhesive polyurethane film (OpSite) and suction bottle, as advised by Singh et al,39 is cost effective and can be adjuvant management of chronic infected wounds. Though doubts have been raised recently,27 topical negative pressure applied over the wound surface is supposed to increase circulation and granulation tissue, and decrease the bacterial count in the wound.
The conventional negative pressure dressing described by Mullner et al40 has the disadvantage of no access to the wound for the surgeon to daily irrigate the wound with local anti-microbial agent of his choice like that in LAD. However, Silverlon® (Argentum Medical, Willowbrook, Ill) that continuously emits a very high level of ionic silver into the wound bed may be placed under negative pressure dressing for better infection control for 1 week.41 The second tube of the LAD is help-ful in changing the wound environment and to some extent guards against the problems of tube blockage due to thick secretion and slough.
Others25,26,42,43 have used topical negative pressure foam dressing with continuous suction between 50 mmHg–125 mmHg.With LAD as low as 30 mmHg, topical negative pressure produces satisfactory results (see Results section).
In LAD II, the bad odor was attributed to chemical (present in the wound and body secretion) degradation of nonviable tissue, discharge and degradation of shed surface epithelium.The problem of odor was reduced by daily saline LAD wash.To reduce the smell at the time of removing the LAD,multiple punctures were made in the polythene sheet and tubes were connected to wall suction (central suction) for 5 minutes.
Consistently better graft take under LAD appeared to be due to control of infection and intermittent compressions of graft between polythene sheet and recipient area, which squeezes any collection under the graft and removed by the suction.Téot et al,44 recently reported a strong correlation between the positive clinical effects of the VAC system and high levels in the wound of proangiogenic growth factors, such as vascular endothelial growth factor (VEGF).44,45 High VEGF may also be responsible for better graft take.
In LAD IB and LAD II, the wound is covered with a polythene sheet that is not permeable to water vapor. In these designs the moisture was removed intermittently along with secretions by negative suction. LAD was also useful to keep the exposed tendons and periosteum viable by providing moist environment until definitive cover is provided. The pus like gel (usually a source of concern to the patients) produced due to combination of hydrocolloid material and wound secretion in hydrocolloid moist dressings was absent in LAD.The negative pressure appears to provide a competitive alternate negative channel for lymphatics and venules (channels for bacterial invasion), therefore, instead of invading the tissue, microorganisms under influence of negative pressure are directed towards the suction bottle for safe disposal.
In the present study, the average number of days required to prepare the wound under LAD was 17.05. Overall graft take under LAD was 99.87%.Twenty-four of 39 wounds (24/39) on an average 33.83 days with conventional dressing (range 7 to 120 days; median 22.5 days) did not achieve healthy granulation fit for skin grafting, but when switched to the LAD,wound preparation took an average of 13.2 days (range 3 to 32 days; median 12 days).
Overall, the LAD was found to be a safe and effective alternative to conventional dressing methods.
LAD application was easy and retained all the advantages of moist wound healing and negative pressure dressings and avoided all of their disadvantages by manipulating the wound environment by providing limited access through tubes.
The wound isolation and safe disposal of infected materials associated with Limited Access Dressing usage helps reduce hospital-acquired infections. It is believed that the LAD minimizes multi-drug resistant bacterial infection and is treated more effectively by physical agents (eg, photon energy, ultrasound, and changes in osmosis and pH) within the closed space of the LAD.
Effective infection control under LAD may be exploited to start radiotherapy and chemotherapy relatively early on in the postoperative period. Preparation of irra-diated wounds for surgery with LAD is quicker than that of conventional dressing techniques (Figure 8).
Intermittent negative pressure with the LAD II may be used to treat DVT prophylaxis.46 Continuous intra-LAD cold saline irrigation may be useful in controlling malignant hyperthermia.