The Role of Negative Pressure Wound Therapy in Healing Wounds
by Bruce E. Ruben MD
Little has been shown by specific randomized controlled trials to effectively speed the healing of a non-healing wound. Biologically, the human body is capable of healing once constitutional barriers are relieved. These barriers include venous and arterial insufficiency, nutritional deficiency, deep-seated infection, and environmental barriers such as repetitive trauma.
Many medical solutions are available to treat and eradicate these conditions and to allow normal wound healing to take place. Still, advanced technologies such as negative pressure wound therapy (NPWT) continue to be one of the most popular advanced wound technologies for a myriad of wound conditions including open abdominal wounds, traumatic wounds, venous ulcers, skin grafts, pressure ulcers, burns, flaps, dehisced wounds, chronic wounds and acute wounds.1 Holding steadfast to my mantra that once the body is restored to homeostasis, most wounds should heal in a 3-4 week span, NPWT may only be a potentially beneficial adjunct and not the cure.
The History of Negative Pressure Wound Therapy
Historically, mechanical forces have been used both outside and inside medicine for hundreds of years to create and expand skin. Outside of medicine, women in Ethiopia used ceramic plates to expand the diameter of the lower lip. Inside of medicine, applied forces have been used to lengthen bone while rubber balloons and other expanders have been used by plastic surgeons to stretch skin.
After all, obesity and pregnancy demonstrate the skin's ability to expand. So it follows that suction or negative pressure applied to large deformities in soft tissue should promote soft tissue genesis beyond the body's ability to do so for itself. Consequently, in 1997, Argents and Morykwas2 were the first to describe the use of mechanical suction or negative pressure applied to a wound in the form of foam, sealed against non-healing skin. They showed that the suction device's negative atmospheric pressure promoted granulation tissue and wound healing.3
Negative pressure wound therapy, as it was termed, was approved as a class II device by the FDA through a process of reviewing the manufacturer's intended use, indications for use and safety for use. This approval for wound suction devices and the 1,500 dressing types in the United States, however, was solely determined through observational evidence based on large, human databases, subjective observation, and historical guidance of similarly used products and devices. It doesn't get more sophisticated than that. This standard of review by the FDA for devices is far less rigorous than the standard that is required for medical products such as cardiac medications, antibiotics and other new drugs. What's markedly different is that for the latter, the FDA requires demonstration of both safety and efficacy through rigorous randomized controlled trials.
Furthermore, included in this menagerie of advanced wound products and technologies are biologics, including growth factors, stem cells, bioengineered skin and dermal scaffolds. As a result, market penetration of NPWT and biologics have skyrocketed. Further, financial support has allowed bench science to document macro and micro environmental responses to mechanical suction. These are just a few reasons that these products are becoming more popular in wound healing.
So, what are the intended uses and indications of NPWT?
Intended Uses of Negative Pressure Wound Therapy
- Skin production or wound shrinkage through applied suction: Transmission of force over a specific surface with its varying elasticity will induce tissue stretch and ultimately lead to wound contraction. Lack of oxygen at the wound surface is suggested as the physiological basis for angiogenesis (new blood vessel formation) and granulation tissue growth. To a layperson, this seems like a spectacular answer for wound healing. Based on this information, one begins to wonder how our body could ever heal without negative pressure wound therapy.
- Fluid removal and edema reduction: Excess extravascular fluid build up has been a well-accepted contravening factor in healing. Removing fluid reduces compression on the blood vessels and improves blood perfusion which promotes the healing process. This intended use of negative pressure wound therapy makes a lot of sense. Similarly, Complete Decongestive Therapy (CDT) is the current standard for controlling edema and healing venous ulcers. This includes manual lymphatic drainage, pneumatic compression, compression bandaging, and diuretics. However, these man-made measures simply deal symptomatically with the issue at large and does not address the root cause, venous reflux disease. In simple terms, vacuum assisted suction compares to putting a pail under a leaking pipe and CDT is like wrapping duct tape around the leak. Minimally invasive venous ablation of the effected superficial veins and perforators shuts off the hose. This is the most direct means of restoring homeostatic venous return and diminishing edema.
- Stabilization of the wound environment: Controlling the wound environment and protection of both the surrounding skin and the wound bioburden is an important intervention and intended use of NPWT…that is, if the practitioner is focused only on the wound and not underlying root causes of non-healing.
Additionally, wound infection prevention is also a purported benefit of the cellophane cover used in the application of NPWT. From an infectious disease perspective it is unclear that NPWT or any dressing prevents infection. All wounds and their surrounding skin are colonized with skin flora, such as S. epidermitis, S. aureus, Strep species, etc. Colonization is not the same as invasive disease, which may not be avoidable in any open or covered wound, acute or chronic. In fact, the body's intrinsic system in place that prevents invasive disease extending below and around the wound bed is 11 trillion neutrophils made fresh daily that infiltrate and sentry the wound base, engulfing invading bacteria like piranhas. Without first restoring arterial and venous flow, it hardly seems plausible that a suction device would be the preferred antidote to 11 trillion white blood cells or restoration of the arterial and venous circulation. The best dressing that exists and the one that was meant for mankind is an eschar or commonly known as a "scab." There is just no man-made substitute for this biologic wonder, and at no cost to the medical system.
Indications of Negative Pressure Wound Therapy
Once indicated, NPWT is for use on large, soft tissue deformities that are not amenable to surgical repair that would or could avail itself to healing more expeditiously. High-level studies as mentioned are few in number but are not absent. For example, one study done of 162 randomized patients with transmetarsal amputations and diabetes randomized to moist wound dressings vs. NPWT did show faster rates of healing with NPWT. Patient comorbidities were similar regarding arterial flow and nutrition. However, total contact casting (a standard) was not the offloading mechanism of choice, venous reflux was not addressed, and osteomyelitis, a contraindication to NPWT, was not evaluated.4
It seems that the largest deformities that might warrant more expeditious tissue creation would be stage IV pelvic pressure ulcers. These longstanding chronic wounds almost uniformly are associated with osteomyelitis. Two outcomes typically occur when using NPWT in these deformities. The first is that wound contraction occurs but only in a centripetal fashion often leaving an open fistula. This endpoint is expected since permitting continued infectious drainage is the native function for exiting infection to the outside with underlying pelvic osteomyelitis. Second, the device hopelessly fails to remain in place based on the location in the ischial or sacral areas.
1. Necrotic tissue with eschar present or a viable eschar present
2. Untreated osteomyelitis
3. Fistulas present
4. Soft tissue malignancy
5. Exposed blood vessels
6. Exposed nerves
7. Exposed anastomotic site
8. Exposed organs5
There is a parable about a person searching for a valuable coin which he dropped somewhere in Central Park but was searching avidly under one of the park's bright lamp posts just because he could see better there. Devices such as NPWT and advanced biologics such as growth factors, stem cells, bioengineered skin and dermal scaffolds are penetrating the market significantly with eye-catching "before" and "after" photographs. Social conditions in the USA create demand to fix the problem and treat the symptom…and the faster, the better. In reality, these devices pale in comparison to the wonder and infiniteness of the human body's power to heal itself once the barriers or root causes of non-healing are reversed. At best, negative pressure wound therapy and the other advanced wound care technologies available today are adjunctive treatments to healing. Before considering its use NPWT, refer to my first blog on the "Five Reasons Wounds Won't Heal." In other words, don't pass "go" until you have maximized nutrition, circulation, relieved pressure and successfully treated deep-seated invasive infection.
1. http://www.kci1.com/KCI1/woundmanagement: Listing of conditions and wound management using KCI V.A.C.(R)
2. Argenta, L.C. and Morykwas, M.J. Vacuum-assisted closure: a new method for wound control and treatment: clinical experience. Ann Plast Surg. 1997; 38: 563–576 ([discussion 577])
3. Morykwas, M.J., Argenta, L.C., Shelton-Brown, E.I., and McGuirt, W. Vacuum-assisted closure: a new method for wound control and treatment: animal studies and basic foundation. Ann Plast Surg. 1997;38: 553–562
4. Armstrong et al: Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomized controlled trial. Lancet. 2005;366:1704-1710.
5. FDA safety communication: UPDATE on Serious Complication Associated with Negative Pressure Wound Therapy Systems. http://www.fda.gov/MedicalDevices/Safety/Alertsandnotices/ucm244211.htm
About the Author
Dr. Bruce Ruben, internationally known as “The Wound Doc,” is the Founder and Medical Director of Encompass HealthCare and Wound Medicine. Board certified in Internal Medicine, Infectious Disease, and Undersea and Hyperbaric Medicine, Ruben pioneered outpatient IV therapy. He is a member of the Medical and Scientific Advisory Committee and National Spinal Cord Injury Association (NSCIA) board, an advisory board member of WoundSource, and serves on the board of The Emily Stillman Foundation.