3. Construction of peri-wound barrier

We typically will apply a peri-wound barrier made of thin hydrocolloid dressing or waterproof tape (Microfoam, 3M, St. Paul, MN, USA) . The dressing may be cut into strips and applied on all corners of the wound. This barrier helps to reduce the likelihood of migration of the larvae outside of the intended debridement area.

5. Transfer of larvae to dressing prior to application to wound

Larvae may now be applied to the prepared dressing on the Mayo stand.  The number of maggots depends on the area of the wound that you are applying MDT.  When applied there should be a slight gap between the larvae to allow for growth. The actual number can range from 50-1,000 per dressing. This generally amounts to no more than 10 maggots per square centimeter of wound.  We advise that the maggots be applied as close to the center of the dressing as possible, as they tend to rapidly migrate to the periphery of the chiffon. The maggots are supplied in a jar containing approximately 1000 maggots, which can last for at least 48 hours before they need to be discarded. We have found that with appropriate refrigeration, we have been able to double this lifespan.  

7. Application of secondary air-permeable dressing

Finally the foot should be wrapped in a protective gauze layer that is not impermeable to air , as completely occluding the wound to air would cause a buildup of liquefied necrotic tissue that is not conducive for maggot survival.  If the wound is located in an area of pressure strict off weight bearing must be accomplished to avoid disturbing the maggots. Additional recent modifications that we have made that appear to assist in reducing the bacterial burden on the wound has been the addition of silver-based dressings (Acticoat, Smith+Nephew, Largo, Florida, USA) to the dressing as a layer just above the most intimate larvae/chiffon layer.

Aftercare

The patient should return in two to three days for a dressing change. The maggots may be removed from the wound with a saline flush and forceps.  Upon removal the larvae will be at least four times the previous size (about 1 cm in length) and many times their pre-debridement volume.  At this time one may dispose of the larvae in a standard biohazard receptacle and re-evaluate the ulceration. If sufficient debridement has been accomplished at this time a standard dressing may be applied.  If further debridement is necessary then one may reapply the maggots immediately or wait a week before the MDT is continued.  Regardless of whether MDT is to be continued, we have found optimal results in combining MDT with sharp debridement of the often heavily necrotic wounds in which MDT appears to be beneficial. Depending on the size and condition of the ulceration it may require multiple applications and sharp debridements before the result  is adequate.  In a recent prospective studies the average time of treatment for recalcitrant wounds ranged from 1-2 weeks to obtain a clean granular wound.(1-3) In our experience, this is an accurate assessment. However, we have employed weekly doses MDT for more than two months in large, complex wounds.

Dispelling fear and anticipation

While one may surmise that the use of a living organism to debride a wound might prompt anxiety on the part of the patient, we have noted the exact opposite reaction from the bulk of our patients. In actuality, the majority of persons expressing revulsion at MDT have been other health care providers. The most frequent question regarding the use of MDT has concerned the life cycle of the larvae. It should be noted (to dispel fear and anticipation) that the larvae will not undergo metamorphosis inside of a human. The green blow-fly larva has a pupa stage through which it must undergo prior to transforming into a fly. This is generally accomplished by burrowing into the soil.(4) 

Maggot Debridement Therapy (MDT): A Primer

Through much trial and error, we have developed a method for application of larval therapy dressing that has been successful in our centers. We have based this method mainly on published and unpublished descriptions of technique by our colleagues in various centers. This is a seven step process:

1. Manual sharp debridement

The first step in successful MDT is the performance of manual sharp debridement of the chronic ulceration to prepare for the placement of the maggots.  If eschar is present, it should be excised to the greatest extent possible, as larvae do not penetrate it as efficiently as other necrotic tissues.

Conclusion

MDT is an inexpensive and potentially efficient adjunct for debriding chronic intractable wounds of the lower extremity.  It has been our experience that the success of MDT is most dependent on technique.   There is a small learning curve involved with applying the above described dressing.   Once this is overcome, we believe that this modality can be a valuable addition to the armamentarium of the physician and surgeon caring for the at-risk limb. 

Maggots are available from:

Monarch Labs (USA)

Biomonde (Germany)

References

1. Mumcuoglu KY, Ingber A, Gilead L, Stessman J, Friedmann R, Schulman H, Bichucher H, Ioffe-Uspensky I, Miller J, Galun R, Raz I: Maggot therapy for the treatment of intractable wounds. Int J Dermatol 38:623-627, 1999

2. Rayman A, Stansfield G, Woolard T, Mackie A, Rayman G: Use of larvae in the treatment of the diabetic necrotic foot. Diabetic Foot 1:7-13, 1998

3. Vistnes LM, Lee R, Ksander GA: Proteolytic activity of blowfly larvae secretions in experimental burns. Surgery 90:835-841, 1981

4. Shinkman R: Worms and squirms. Maggots, leeches are making a comeback in modern medicine. Mod Healthc 30:54-55, 2000

2. Application of skin preparation

The next step is the application of skin adhesive to the peri-wound area. This will facilitate adhesion of the peri-wound barrier.

4. Preparation of nylon chiffon dressing to accept larvae

A nylon chiffon dressing, which is available directly from the Monarch Laboratories, is used to accept and contain the larvae on the tissue intended for debridement.  This chiffon dressing is generally laid out over a few pieces of moist gauze dressing and laid on a Mayo stand within easy reach of the wound.

6. Application of MDT dressing to wound with water resistant foam tape

The next step is to transfer the prepared maggot/chiffon/4x4 dressing to the wound.  Obviously, this should be done as expeditiously as possible to avoid unwanted migration. Water resistant foam tape (Microfoam, 3M, St. Paul, MN, USA) should then be used to secure the ends of the dressing.