EQUINE VETERINARY EDUCATION / AE / JANUARY 2020


15


a)


animals and the fact that the canister would often be full of discharge at or around 72 h of use (Stanley 2017). The use of intermittent or continuous negative pressure and the amount of negative pressure requires further study in the horse. A silver impregnated foam was placed in the wounds as all


b)


three were chronically infected. The horses did not have clinical signs of cellulitis around the wound area and antibiotics were not routinely administered or judged to be necessary. As the NPWT removes the discharge, it provides excellent drainage. At the time of the first dressing change after NPWT was started (3–4 days after NPWT and around 8–10 days after surgery) the wounds appeared healthier with red granulation tissue starting to appear (Fig 4). This may have been coincidental with increasing time after surgery, however the subjective impression of improvement in the appearance of the superficial infection with NPWT remained strong. Studies have been performed evaluating the effect of NPWT on infection and are controversial. Some studies show a potential enhanced bacterial clearance and diminished infection whilst other studies show higher bacterial numbers with NPWT (Moues et al. 2004; Weed et al. 2004; Lalliss et al. 2010; Demaria et al. 2011). Silver impregnated foams are reported to enhance the removal of bacteria when used with NPWT (Stinner et al. 2011; Stanirowski et al. 2015). The effect of NPWT on equine infected wounds remains to be elucidated as does the effect of different foams. In a recent study of different foams and NPWT in an equine ex vivo wound model, silver impregnated foam was effective at reducing Pseudomonas infection but not MRSA (Van Hecke et al. 2016). In that study polyvinyl alcohol foam was the most effective in reducing both types of bacteria in the wounds. The effect of foam type on different bacterial populations and wound healing with NPWT requires further study in horses prior to any recommendations being made as to the optimal foam to be used. There were no control horses with which to compare


c)


these three horses so the results are purely subjective in nature. The granulation tissue which formed in the wounds during NPWT was solid and red, healthy in appearance, and healing progressed rapidly. This is subjective and no horses were treated with surgery and traditional wound care after dehiscence to provide a comparison. Primary surgical excision has been used successfully in four reported cases and by the authors themselves but these three horses had particularly advanced and chronically infected, open bursitis and primary surgical excision had failed (Honnas et al. 1995). The healing of subcutaneous olecranon bursitis can be


impeded when the horse lies down repeatedly and re- traumatises the area with a hoof. These horses were not routinely cross-tied but did not show an inclination in the hospital for repeated or prolonged episodes of recumbency. Cross-tying or tying to an overhead wire to prevent recumbency could be considered if the dressing was repeatedly disrupted by this activity. The use of the overhead hook, normally employed for fluid administration in our hospital, to suspend the NPWT apparatus and canister facilitated its application and allowed the horses to move


Fig 4: The progression of healing with NPWT for Horse 2 from the first bandage change. A progressive decrease in size is noted


with the appearance of granulation tissue. At the end of 14 days there is obvious wound contraction and progression of epithelialisation at the periphery.


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