Topical negative pressure therapy: current concepts and practice.
Abstract: Research into topical negative pressure therapy (TNPT) started in 1989 with Dr Louis Argenta and Prof Michael Morykwas of Wake Forest University School of Medicine in North Carolina, USA.

In 1997, Morykwas and Argenta concluded that TNPT both enhanced granulation tissue formation and helped bacterial clearance, through the actions of negative pressure Armstrong and Lavery confirmed this in 2005, concluding that TNPT therapy was promoting the development of granulation tissue

Numerous other studies have proved that TNPT is beneficial for a myriad of other wounds including: sternotomy wounds, extensive de-gloving injuries, various soft tissue injuries prior to surgical closure, )skin grafting, pressure sores, leg ulcers, sacral pressure ulcers, acute traumatic soft tissue defects, and soft tissue defects following rigid stabilisation of lower extremity fractures.

This review aims to summarise the clinical and scientific concepts of TNPT and its future applications.

KEYWORDS Topical negative pressure therapy / TNPT / Wound management, Dressings / Tissue healing, Granulation tissue
Article Type: Report
Subject: Wounds and injuries (Research)
Bedsores (Research)
Skin
Medical colleges
Authors: Malahias, M.
Hindocha, S.
Saedi, F.
McArthur, P.
Pub Date: 10/01/2012
Publication: Name: Journal of Perioperative Practice Publisher: Association for Perioperative Practice Audience: Academic Format: Magazine/Journal Subject: Health; Health care industry Copyright: COPYRIGHT 2012 Association for Perioperative Practice ISSN: 1750-4589
Issue: Date: Oct, 2012 Source Volume: 22 Source Issue: 10
Topic: Event Code: 310 Science & research
Accession Number: 309315290
Full Text: History

Research into TNPT started in 1989 by Dr Louis Argenta and Prof Michael Morykwas of Wake Forest University School of Medicine in North Carolina of the USA.

A German trauma surgeon first described the benefits of exposing a wound to negative pressure for prolonged periods of time: Fleischmann et al published their findings in 1993 (Fleischmann et al 1993), after successfully making use of this technique in 15 patients with compound fractures.

In 1997, Morykwas and Argenta concluded in a study, that TNPT both enhanced granulation tissue formation whilst at the same time helped bacterial clearance, through the actions of negative pressure (Morykwas et al 1997, Argenta & Morykwas 1997, 2005). Armstrong and Lavery confirmed this in 2005; they concluded that TNPT was promoting the development of granulation tissue (Armstrong & Lavery 2005).

How does TNPT work? A technical view

Machine

The TNPT machine has a pressure monitor and adjusts pressure continuously to ensure that the therapeutic pressure range is delivered to the wound. It compensates automatically for the pressure change due to unit positioning and increased exudate production. The inbuilt digital processor allows the clinician to monitor the delivered therapy history; the device will sound an alarm if the canister is full or not engaged, or if any seal leaks or tube blockages occur, if the battery charge is low, or the suction pressure is lost (VAC ViaTM Therapy System Monograph).

Consumables

Dressing

The dressing is made of reticulated, hydrophobic open-cell foam with pore sizes of 400-600 microns, allowing cellular microdeformation under controlled negative pressure (VAC Via Therapy System Monograph). The semiocclusive drape provides an appropriate seal for the transmission of negative pressure to the wound site, whilst maintaining a moist wound bed. The connector pad, with the tubing has special sensors, which allow the pump to maintain target pressure in the wound.

Canister

This container is a single use, plastic container with welded connection and valve to prevent leakage. It contains a powder like substance, containing 'Isolyzer', which is a chemical that solidifies fluid waste. The T.R.A.C[TM] Pad, formed of a clamp and tubing with special sensors, allows the pump to monitor and regulate the pressure.

How does TNPT work? A physiological view

Julius Wolff observed in 1892 that bone under stress would change its shape if exposed to this physical force of nature for long enough; this is what we today call 'bone remodeling', commonly known as 'Wolff's law' (Wolff 1892, Brand & Claes 1989). A few years later in 1896 another German scientist observed a similar response in soft tissues. Richard Thoma (Thoma 1896) evaluated the effect of dynamic forces acting on the walls of blood vessels. He concluded that an increase in lateral pressure of the vessel wall caused it to thicken; an increase in end pressure, on the other hand, resulted in the formation of new capillaries. This is the law of tension stress described by Ilizarov (Ilizarov 1989) and forms the scientific basis for the Ilizarov bone lengthening technique.

Granulation tissue

TNPT therapy is useful in promoting granulation tissue formation. This was proven after a porcine study model involving 25 pigs (Morykwas et al 1997) in which laser doppler probes were placed inside surgically created wounds and the blood flow was studied.

The authors found that when negative pressure was applied in 25mmHg increments up to 400mmHg (lasting for 15 minutes) the optimal maximal improvement of blood flow was 125mmHg, which resulted in an increase in blood supply of 400%. This was proven by comparing the production rate of granulation tissue between intermittent and continuous suction, by measuring the reduction of wound dimensions over time (Morykwas et al 1997).

The increased blood flow is only sustainable for approximately five minutes before it declines. In order to avoid the decline, the pressure has to be intermittent. Pausing suction cycles for at least two minutes between each application, at 125mmHg (if tolerated by the patient) results in the best outcome from TNPT Therapy (Morykwas et al 1997).

Two possible explanations for this observation were proposed by Philbeck et al (1999). These authors suggested that intermittent episodes of negative suction, prevented the process of capillary autoregulation from adapting to the negative pressure. The rhythmic perfusion environment is thought to promote granulation tissue formation, through an increase in capillary end pressure that results in the formation of new capillaries. The authors also proposed that intermittent stimulation allows the cells time to rest and to prepare for the next cycle of cell division, similar to cells undergoing mitosis.

Wound environment

TNPT has also been shown to clear excess moisture (Rosenfeldt 1989, 2003) leaving behind a humid wound. Advantages of this include reduced pain and decreased susceptibility to infection (Haimowitz & Margolis 1997). In addition, it prevents the formation of eschar, which would delay epithelial migration; therefore enabling wound healing to occur more swiftly than in dry wounds (Weiss et al 1990).

Exudate/oedema

Tissue exudate or oedema results in an increase in interstitial pressure; this in turn can cause occlusion of the microvasculature and lymphatics which results in a lack of nutrient and oxygen delivery to the tissues. Secondary to this, there is an increased bacterial count together with an accumulation of metabolic waste products. This leads to the release of protein degrading enzymes, causing further necrosis of tissues, through increased inflammation and proteolysis (Abbott et al 1998). The TNPT system facilitates the removal of excess interstitial fluid and may therefore improve some of these parameters.

Bacterial load

Morykwas et al (1997) inoculated surgical wounds in five pigs, with 108 infecting organisms. This was followed by the application of 125mmHg negative suction to some of these wounds. Full thickness biopsies from each of these sites were harvested every 24 hours. Between days four and five, wounds treated with TNPT therapy showed a reduced bacterial load by 105.

TNPT has also been shown to effectively treat osteomyelitis and soft tissue infections, following adequate surgical debridement of nonviable tissue and appropriate antibiotic cover (Wongworawat et al 2003, Page et al 2004, Bernstein et al 2005, Datiashvili & Knox 2005, Geller et al 2005, Mendonca et al 2005, Repta et al 2005, Archdeacon et al 2006, Pelham et al 2006).

Uses of TNP therapy:

Molnar et al (2000) first reported the benefits of grafting scalp lesions with superficial skin grafts and concomitant TNPT therapy. If theses scalp wounds cannot be closed with a flap, the outer surface of the skull diploe is normally removed, exposing cancellous bone. This will result in increased granulation, forming a favorable vascular bed (a week or two later), which will be more amenable to skin grafting. Without this two stage procedure, the graft take is usually very poor and more likely to fail (Molnar et al 2000).

Numerous other studies (Argenta & Morykwas 1997, Morykwas et al 1997, The Weinberg Group Inc 1999, Deva et al 2000, DeFranzo et al 2001, Scherer et al 2002, Kamolz et al 2003, Page et al 2004, Armstrong & Lavery 2005, Molnar et al 2005, Schwien et al 2005, Stannard et al 2006, Andrews et al 2006, Frykberg & Williams 2007) have proved that TNPT is beneficial for a myriad of other wounds, including:

* sternotomy wounds (Tang et al 2000a,b, Obdeijn et al 1999)

* extensive de-gloving injuries (Meara et al 1999, DeFranzo et al 1999)

* various soft tissue injuries prior to surgical closure (Bauer et al 1998)

* skin grafting

* pressure sores (Collier 1997, Deva 1997, Hartnett 1998, Baynham et al 1999, Greer et al 1999, Mendez-Eastman 1999)

* leg ulcers (Mendez-Eastman 1999)

* sacral pressure ulcers

* acute traumatic soft tissue defects

* soft tissue defects following rigid stabilisation of lower extremity fractures (Mullner et al 1997).

Indications and contraindications for TNPT

The indications and contraindications for TNP therapy are summarized in Tables 1 and 2. The indicators for particular caution in relation to the use of TNP are given in Table 3.

Use of TNPT in perioperative practice

The increase in the use of TNPT means that fewer and fewer complex reconstructive procedures are likely to take place. Wounds which previously would have been managed with free flap surgery or similar have now been replaced with much simpler procedures like split thickness skin grafting after the TNPT device has provided a granulated wound bed.

This means that for the perioperative practitioner, knowledge of this device is imperative, as surgeons will seek to apply and remove this device frequently in the operating theatre, in the recovery area or on the ward prior to surgery. As a result operating knowledge such as pressure setting levels, and absolute contra-indications to the use of TNPT should be known to the general operating room team.

Perioperative practitioners may be requested to aid in the management of TNPT devices, such as when there is a leak between the wound and the TNPT dressing (Figure 1), or when there is a complication like bleeding and the TNPT device has to be removed in an emergency. The general set up of how the dressing is applied and how the machine is kept is important to the perioperative practitioner. A TNPT should not be an alienated device, as its revolutionary development will now spread across all operating rooms globally.

[FIGURE 1 OMITTED]

Clinical trials and scientific advancements

The TNPT Via[TM] Therapy Unit is a compact size, single use, and disposable TNPT device. It has been designed to be used on low exudating (<80 mL/day), small to medium sized wounds. It delivers continuous sub-atmospheric pressure of 75mmHg to 125mmHg with a seven day therapy life, enabling earlier discharge of patients into the community (VAC Via[TM] Therapy System Monograph).

Another advance is the instillation of antimicrobials into the sponge and this has continued to broaden the TNPT's usefulness (Robert & Thomas 2007).

In 2005 Armstrong and Lavery (2005) performed a 16 week randomised trial to compare the TNPTuum Assisted Closure Therapy System [KCl] with standard wound therapy. They focused on the treatment of amputation wounds of the foot in patients with diabetes. Eighteen health-science centres, including diabetic foot clinics, wound clinics in the private sector and academic health-science centres across the USA, participated in the trial. A total of 162 patients were recruited and randomly allocated to a treatment, with a ratio of study patients to controls of 1:1.

The primary objectives of the study were to determine whether negative pressure wound therapy, delivered by the TNPT system, was clinically effective in treating amputation wounds of the diabetic foot. In addition, whether it would increase the proportion of wounds, with complete closure.

A greater proportion of patients had healed wounds in the negative pressure wound therapy group than in the control group ie: 43 patients (56%) vs 33 patients (39%) [p=0.040]. Treated patients also achieved complete wound closure in a significantly shorter time than control patients (p=0.005).

The study population included patients with wounds that were larger and more complex than those from previous randomised trials (Veves et al 2002) which gives this study additional characteristics that differentiate it from previous studies in this field.

Conclusion

The EBM reveals level1+ evidence (evidence based medicine high quality meta analysis) that TNP therapy is an efficient method for managing wounds. Negative pressure wound therapy, as delivered through this system, seems to be a safe and effective treatment for complex diabetic foot wounds. Treatment with negative pressure wound therapy resulted in a higher proportion of wounds that healed, with faster healing rates.

There is a growing range of devices available based on the concept of wound suction, however the TNPT device has gained increased popularity among users over the past decade. This is mainly because the body of supportive evidence is one of the most substantial in the wound care industry (Chaby et al 2007, Willy et al 2007) including several randomised controlled trials and numerous peer reviewed articles (Jeschke et al 2000, Joseph et al 2000, McCallon et al 2000, Ford et al 2002, Eginton et al 2003, Wanner et al 2003, Moisidis et al 2004, Moues et al 2004, Armstong & Lavery 2005, Timmers et al 2005, Braakenburg et al 2006, Stannard et al 2006, Vuerstaek et al 2006, Blume et al 2008, Wild et al 2008).

According to these reviews, there is much to be excited about with the increased diversity of TNP applications, but there is also a need for more scientific evidence to support the growing number of case studies. Further research on TNPT is required; future work should look at the effect of rapid healing on cost efficacy, length of hospital stay, and effectiveness, as well as quality of life.

There is also a need to evaluate these systems for patient acceptability and clinical effectiveness. Clinicians need to know which device will be the most cost effective, clinically effective and tolerable for patients.

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by M Malahias, S Hindocha, F Saedi and P McArthur

Correspondence address: Sandip Hindocha, Department of Plastic Surgery, Whiston Hospital, Warrington Road, Liverpool, L355DR hindocha2001@yahoo.com

About the authors

Marco Malahias

MBBCh (Hons), MRCS (Ed)

Senior Microvascular Fellow, Good Hope Hospital, West Midlands

Sandip Hindocha

MD, MBChB, MPhil, MRCS

SpR Plastic Surgery, Whiston Hospital, Prescot

Farid Saedi

MBChB

Clinical Fellow in Burns and Plastic Surgery, Whiston Hospital, Prescot

P McArthur

Department of Plastic Surgery, Countess of Chester Hospital

No competing interests declared

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Provenance and Peer review: Unsolicited contribution; Peer reviewed; Accepted for publication January 2012.
Table 1 Indications for TNP therapy

1  Diabetic foot wounds

2  Acute and traumatic wounds

3  Dehisced surgical wounds

4  Partial-thickness burns

5  Flaps and grafts

6  Chronic wounds

7  Pressure ulcers

Table 2 Contraindications for TNP therapy

1  Malignancy in the wound

2  Untreated osteomyelitis

3  Unexplored fistulae

4  Necrotic tissue with eschar present

5  Exposed organs and blood vessels

Table 3 Indicators for caution with TNP therapy

1  Poor haemostasis

2  Anticoagulants

3  Platelet aggregation inhibitors
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