The effectiveness of cathodal electrical stimulation in pressure ulcer treatment

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Pressure ulcers are a serious condition that is particularly common among frail elderly people, hence the development and implementation of effective therapies is a pressing issue. Concerning pressure ulcers that resist standard wound care (SWC), the National and European Pressure Ulcer Advisory Panel guidelines (2009y) recommend using electrical stimulation (ES). According to various authors, ES can be applied at different stages of wound healing: 1) to promote autolysis and/or reactivate the early inflammatory phase, 2) to promote the antibacterial effect, 3) to reactivate the anti-inflammatory effect, 4) to stimulate granulation tissue growth, and 5) to promote re-epithelialization. However, the precise rules for treating wounds with ES still need to be developed and confirmed in clinical research. The authors of in vitro and in vivo studies point to the migration of cells involved in tissue repair toward the anode or cathode created by an electrical field delivered into a tissue culture. In cell cultures, the anode enhances the motility of macrophages and neutrophils, but human keratinocytes, fibroblasts and bovine corneal epithelial cells migrate directionally toward the cathode. As regards in vivo studies, it has been shown that the application of electric current significantly increases the synthesis of adenosine triphosphate (five-fold) and protein (by 70%). ES of fibroblasts improves collagen synthesis. Studies have also shown that ES stimulates angiogenesis and improves blood flow. It is commonly recognized that cells involved in tissue repair require oxygen to function more efficiently. The results of studies in diabetic patients and in individuals with spinal cord injury (SPI) indicate that ES facilitates a temporary increase in local tissue oxygen tension. The National and European Pressure Ulcer Advisory Panels recommend using electrical therapy for treating chronic and/or recurrent stage II, III and IV pressure ulcers. In his literature review of 2005, Kloth, too, justifies the use of electric charges for wound healing, particularly in the case of chronic wounds in which the natural low of bioelectric currents may be disturbed by tissue desiccation, residue from heavy metals (e.g. iodine, silver), the presence of nonconductive petrolatum in some impregnated dressings, and debriding enzymes. In those cases, ES can restore natural electric potentials and intensify healing processes. Electrical stimulation with high-voltage pulsed current (HVPC) appears to be a particularly promising method of wound treatment. However, even though studies show HVPC as an efficacious wound treatment modality, the methodology of its application has not been established to date. Clinical studies are not unanimous about what polarity the treatment electrode should have. Some authors use only one polarity of the treatment electrode for the length of treatment, more frequently choosing the cathode, than the anode. In other studies, both these electrodes were used over the period of treatment. Franek et al. applied the cathode for the first 2 weeks on average and then replaced it with the anode until the end of treatment. In the study by Houghton et al., cathodal stimulation was applied for the length of the first week and then the polarity of the electrodes was reversed weekly. The series of in vivo studies with animals that Brown et al. conducted in the years 1987-1995 has demonstrated that the negative electrode was effective in the early stages of wound healing. In the first 4 days of treatment, cathodal stimulation considerably accelerated the healing of new incisions made in rabbits. Seven days after the experiment commenced the cathode was found to inhibit the healing process. Anodal simulation was not found to be effective during the first four days of treatment, but in the later period it considerably accelerated the re-epithelialization of wounds. In both Mertz et al. and Brown et al. studies the authors have demonstrated that the anode is effective at later stages of wound treatment, that it can promote the re-epithelialization of wounds, and that ES is the most effective when first the cathode and then the anode are used. An in vivo study conducted by Zhao et al. has made him conclude, though, that as epithelial cells are attracted to the cathode it is the negative electrode that can effectively promote epithelialization. Mehmandoust et al. who have investigated the effects of anodal and cathodal ES on acute wound healing have concluded that ES can significantly decrease wound surface area and make wounds close faster regardless of the treatment electrode polarity, however anodal stimulation applied for the first 3 days and then replaced by cathodal stimulation for the remainder of treatment may strengthen tissue repair. The conclusion of the Talebi et al. study has been that anodal ES is capable of improving the healing of acute skin wounds, because it causes the wound surface to close and the wound potential to return faster to the preinjury level. In their randomized in vivo study with rats, Borba et al. have demonstrated that anodal stimulation has positive effect on neoangiogenesis in the early stage of acute experimental wound healing. According to their trial, preoperative anodal stimulation can be instrumental in treating early/acute stages of wounds. The results of Bourguignon et al. in vitro study with human fibroblasts indicate that the maximum stimulation of protein and DNA synthesis is obtained at 50 V and 75 V at cells located to the negative electrode. In the clinical study conducted by Franek et al., cathodal stimulation was observed to promote the growth of granulation tissue in venous leg ulcers. The study by Asadi et al. has showed that cathodal sensory ES increases the release of vascular endothelial growth factor (VEGF) in skin. Clear guidelines on how anode and cathode should be best used to treat wounds in humans are still to be developed. The results of in vitro and in vivo studies indicate, though, that both the electrodes promote wound healing and that the polarity of the treatment electrode should be matched to the wound healing stage. Therefore, more experimental and clinical research is needed to provide evidence giving a better insight into how cell migration is affected by a sequence of polarities or other factors. Until this knowledge is acquired, the polarity of the treatment electrode will have to be selected based on the outcomes of experimental and clinical studies and best practice.

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