EUROPEAN TISSUE REPAIR SOCIETY

PHYSICAL FORCES II

PHYSICAL FORCES II

BIOLOGICAL MONITORING OF WOUNDS TREATED BY NEGATIVE PRESSURE

Introduction

The wound ecosystem is essentially made of cells, cytokines and bacteria. Some of the factors influencing wound healing are now identified although their interactions are poorly understood. Others may still be undiscovered. We are walking on the moon in our knowledge of wound healing, particularly chronic wound healing.

Fluid analysis shows that the chronic wound bed is exposed to a hypoxic,¹ proteolytic environment² which degrades components of the extracellular matrix.³ There is also a greater concentration of inflammatory mediators than in the acute wound.⁴

Vacuum Assisted Closure (VAC) applied to wounds, improves the tissue perfusion, decreases oedema and infection. ⁵ We collected the exudates from thirty-four wounds treated by negative pressure. Samples were sent for bacteriological and biochemical analysis.

Material and methods

Exudates from eight subacute (i.e., delayed healing of acute wounds) (one upper limb trauma, one buttock avulsion, three lower limb traumas, three abdominal dehiscences) and twenty-six chronic (fifteen pressure sores, nine venous and two radiotherapy ulcers) wounds were collected in the tubing immediately after cleaning the wound with saline and changing the foam. Samples were sent for the following analyses.

Bacteriology

Quantitative analysis was performed and qualitative comparison was made with the bacteria found on swabs from the wound before its cleaning.

Electrolytes and protein content

The concentration of electrolytes and proteins in the exudates was compared to that of the blood.

Growth factors

Epidermal growth factor (EGF), Fibroblast growth factor (FGF), Transforming growth factorb (TGFb), Platelet-derived growth factor (PDGF) were titrated by the Elisa (Enzyme- linked immunoabsorbent assay) test.

Proteases

Metalloproteases (MMP)-13, MMP-8 and one of their inhibitor MMP-1 were titrated by the Elisa test

Results

Bacteriology

In most of the wounds, the bacteria were identical in both the swabs and the exudates. During treatment the predominance of specific bacteria varied: various strains appeared and disappeared. The colonisation decreased in wounds which responded to treatment.

Electrolytes and proteins

Table 1 shows the comparison between the concentration of electrolytes and proteins in the exudates and blood of six patients. As expected the protein concentration was high in the exudates; in a highly exudative wound negative pressure may create an electrolyte imbalance which induces cardiac arrythmia (Figure 1).

Growth factors

TGFâ is the only growth factor which shows a reproducible correlation with the evolution of the wound; indeed, its level in the exudates decreases in wounds which respond to therapy. The values of the three other growth factors were not significant.

Proteases and antiproteases

There is a constant correspondence between the favourable evolution of the wounds and the re-establishment of the balance between proteases and anti-proteases with a decrease of the proteases and an increase of their inhibitors, tissue inhibitors of metalloprotease (TIMPs). To illustrate the biological monitoring of wounds treated by negative pressure, three clinical cases are now presented.

Case 1

A kidney transplant patient presented with a wide abdominal dehiscence after emergency surgery for acute abdominal necrosis; negative pressure was applied to the omentum (Figure 2). Within ten days good granulation tissue was obtained and a meshed skin graft applied (Figure 3). The number of enterococcus colonies, progressively decreased. The level of TGFâ decreased (Figure 4a) and the balance of proteases – antiproteases changed with a decreased production of proteases and simultaneous increased production of antiproteases (Figure 4b).

Case 2

A 43-year-old paraplegic man suffered from a perineal pressure sore; he was treated for an occlusion of the iliac vessels which required vascular surgery prior to reconstruction of the pressure sore. During that period, negative pressure was applied to the wound which responded poorly. The load of staphylococcus aureus progressively increased. The level of TGFâ increased (Figure 5a) as well as the proteases; the antiproteases decreased (Figure 5b). Negative pressure was discontinued.

Case 3

A 41-year-old man suffered a traumatic avulsion of the skin of the buttock. After surgical debridement, good granulation tissue was obtained within a week of VAC therapy (Figure 6a); a meshed skin graft was applied and the negative pressure maintained on the graft for five more days; complete epithelialisation was obtained after that time (Figure 6b). The bacterial count was low during the preparation of the wound bed and no more bacteria could be identified after skin grafting. TGFâ decreased progressively (Figure 7a) as well as the proteases with an increase of their inhibitors (Figure 7b).

Discussion

We were expecting that the comparative bacterial qualitative analysis of the exudates and the swabs would be different, presuming that negative pressure would extract germs from the depth of the wound. Qualitative analyses were similar in the exudates and the swabs which are reliable markers of the wound colonisation. The variations in the bacterial population was remarkable. Some apparently disappear only to reappear later. The wound resembles a battlefield in which the predominance of the various bacteria changes with time.

The bacterial load follows the wound evolution. In highly exudative wounds, negative pressure may induce a severe drop in blood electrolytes, especially hypokalaemia which creates systemic disorders.

There is a constant correlation between the favourable evolution of wounds and the re-establishment of the balance between proteases and antiproteases and a decrease in TGFâ. The analysis of the other growth factors (EGF, FGF and PDGF) was inconclusive; the values were too dissimilar to draw any valid conclusion.

A comprehensive study of the biochemical composition of healing and non-healing wounds highlighted the possibility that biochemical markers could be used to evaluate wound healing. Nevertheless, the relationships between all of them remain unclear. There is a need for an International Conference of experts of various disciplines to discuss these factors in wound healing. Obviously, they cover a small but important aspect of the surgical management of wounds.

Romain Vanwijck
Department of Plastic Surgery
Wound Healing Unit
Cliniques Universitaires St-Luc (UCL)
1200 Brussels
Belgium

References

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