Burn Injuries: Pathophysiology, Treatment and Rehabilitation

By Audrey Ko

A burn injury happens when the skin is in contact with a heat source, including hot water, fire, electricity, and chemicals (Warby & Maani, 2019). While minor burns take few days to heal, severe ones if not managed well could lead to serious complications such as sepsis, multiple organ failure, and even death. To optimise treatment plans, it is therefore important to accurately classify the degree of burn based on how deep the skin tissue is penetrated. Superficial (first-degree) burns involve only the epidermis, the skin becomes red with minor inflammation and pain. Partial thickness (second-degree) burns extend into the dermis, swelling, redness, blistering, and severe pain are common. Full thickness (third-degree) burns are the most severe with all layers of the skin destroyed and nerve endings are damaged causing minimal or no pain sensation (Stanford Health Care, n.d.).  

Our skin being the first line of the body defense mechanism, serves as a protective barrier to hazardous substances. A thermal destruction would remove this natural barrier, causing protein coagulation and necrosis of cells at the burn site. This environment provides a favourable niche for microbial colonisation and proliferation (Church et al., 2006). Moreover, the presence of necrotic tissues substantially compromises the immune defense mechanism: their avascularity inhibits the migration of host immune cells and the delivery of antimicrobial agents to the site (Church et al., 2006). In patients where the colonisation of microorganisms turns into invasion, a burn wound infection occurs. While a breach in the skin integrity would normally activate the “wound healing cascade” involving a series of events aimed to repair damaged tissues (Wilkinson & Hardman, 2020), in deep second-degree and third-degree burns, the skin is incapable to repair itself. In such cases, the cells and tissues required for healing are completely destroyed. Therefore, a reconstructive surgery is urgently needed. 

Skin grafting is the gold-standard treatment for partial- and full-thickness burn injuries. It involves the transplantation of healthy skin from an undamaged donor site to the wound site (Wounds International, n.d.). The prevalence and high mortality of burn injuries in the past decades led to its rapid development and it is now a common practice for severe burn wounds to accelerate healing. Before the grafting procedure can be carried out, the burn wound has to be excised. Necrotic tissues heavily colonized with bacteria are removed as soon as possible to shorten the period of wound inflammation and prevent further infection (Church et al., 2006). The process is repeated until the entire wound is debrided and viable tissue is reached, the wound bed is then covered with new skin grafts. 

A skin graft is a section of the epidermis and dermis which has been completely separated from its blood supply from the donor site. Depending on how much of the dermis is harvested, skin grafts can be classified into split- and full-thickness (Wounds International, n.d.). Split-thickness skin grafts (STSGs) consist of the epidermis and upper part of the dermis, leaving behind sufficient to enable the skin to regenerate and heal itself. Thigh, back, upper arm and abdominal wall are suitable donor sites because they have a broad surface area. STSGs could be further meshed (i.e. insert multiple fenestrations) to cover up to 4 times more the area of the burn wound (Browning & Cindass, 2021). Full-thickness skin grafts (FTSGs) consist of epidermis and the entire dermis. Since no dermis is remained to allow spontaneous regeneration of the skin, the wound must be closed by suturing. Therefore, a donor site must be selected where a small area could be excised and closed with minimal scarring (e.g. ear and scalp). 

As mentioned earlier, transplanted skin does not have its own blood supply and so graft survival depends on the ingrowth of capillaries from the viable tissue in the wound bed. Adherence of the skin graft to recipient site happens in three steps. In the first 24 hours after placement, the graft tissues passively absorb transudate from the wound bed for nutrients and oxygen through a process named “plasmatic imbibition” (Golpanian & Kassira, 2016). The graft is white at this time. “Inosculation” occurs at around 48-72 hours after, a vascular network is established between the capillaries in wound bed and the cut vessels on the underside of the skin graft (Bell Jr., 2020). This stage then transitions into “revascularisation” when the skin graft begins to develop its own network of blood and lymphatic vessels, it gradually takes on colour and becomes red purple (Wounds international, n.d.). Full circulation is often restored within 4 – 7 days. Depending on the size of the graft and patient conditions, it takes 2 – 4 weeks or longer for complete healing. And as the graft matures at its new site, it gets innervated and regains sensation from the sensory nerves of the wound bed (Golpanian & Kassira, 2016). 

While the burn wound has healed, the focus now shifts from surgical interventions to rehabilitation and aftercare. Hypertrophic scarring (HTS) is a major concern following severe burn injuries (Chiang et al., 2016). These scars are the result excess collagen being produced at the injured site during the wound healing process, and are wide, red, thickened, and raised in appearance (Healthline, n.d.). This condition is associated with pain, itching and limited movement when they are present across joints. The maturation of these scars will take up to two years or more until they soften and fade in colour. During this prolonged period, patients may require physio or occupational therapy for their functional recovery to mobilise joints that are affected by HTS. To minimise the formation of HTS, treatments such as compression garment, silicone gel sheets and laser therapy have been proven to be effective (Gauglitz et al., 2011), yet these to varying extents pose inconvenience to the patients’ daily lives. Also, the ultimately unpleasant aesthetic appearance can be a great psychological burden to affected patients (Chiang et al., 2016). Studies have shown that compared to the general population, patients who suffered from severe burn injuries report a lower quality of life and reluctance to return to the society, reasons include but are not limited to pain, discomfort, anxiety and depression (Jeschke et al., 2020). While medical advancements have significantly increased the survival of burn victims, it is clearly important that further changes and support is needed in all phases of their recovery process.

References:

Bell Jr., R. H. (2020) Northwestern Handbook of Surgical Procedures. Florida, CRC Press. 246–247. Available from: doi:10.1201/b17659-109 [Accessed 25 May 2021] 

Browning, J. A. & Cindass, R. (2021) Burn Debridement, Grafting, and Reconstruction. [Online]. StatPearls Publishing. Available from: http://www.ncbi.nlm.nih.gov/pubmed/31869181 [Accessed: 25 May 2021].

Chiang, R.S., Borovikova, A. A., King, K., Banyard, D. A., Lalezari, S., Toranto, J. D., Paydar, K. Z., Wirth, G. A., Evans, G. R. D. & Widgerow, A. D. (2016) Current concepts related to hypertrophic scarring in burn injuries. Wound Repair and Regeneration. 24 (3), 466–477. Available from: doi:10.1111/wrr.12432

Church, D., Elsayed, S., Reid, O., Winston, B. & Lindsay, R. (2006) Burn wound infections. Clinical Microbiology Reviews. 19 (2), 403–434. Available from: doi:10.1128/CMR.19.2.403-434.2006

Gauglitz, G. G., Korting, H. C., Pavicic, T., Ruzicka, T. & Jeschke, M. G. (2011) Hypertrophic scarring and keloids: Pathomechanisms and current and emerging treatment strategies. Molecular Medicine. 17 (1–2), 113–125. Available from: doi:10.2119/molmed.2009.00153

Golpanian, S. & Kassira, W. (2016) Full-thickness skin graft. Springer International Publishing, 199–201. Available from: doi:10.1007/978-3-319-40631-2_48

Healthline (n.d.) Hypertrophic Scar: Treatment, Causes, Image, and More. Available from: https://www.healthline.com/health/hypertrophic-scar-treatment [Accessed: 25 May 2021].

Jeschke, M. G., van Baar, M. E., Choudhry, M. A., Chung, K. K., Gibran, N. S. & Logsetty, S. (2020) Burn injury. Nature Reviews Disease Primers. 6 (1). Available from: doi:10.1038/s41572-020-0145-5 

Stanford Health Care (n.d.) Burn Stages. Available from: https://stanfordhealthcare.org/medical-conditions/skin-hair-and-nails/burns/stages.html [Accessed: 25 May 2021].

Warby, R. & Maani, C. V. (2019) Burns Classification. [Online]. StatPearls Publishing. Available from: http://www.ncbi.nlm.nih.gov/pubmed/30969595 [Accessed: 25 May 2021].

Wilkinson, H.N. & Hardman, M.J. (2020) Wound healing: cellular mechanisms and pathological outcomes: Cellular Mechanisms of Wound Repair. Open Biology.10 (9). Available from: doi:10.1098/rsob.200223

Wounds International (n.d.) What you need to know about skin grafts and donor site wounds. Available from: https://www.woundsinternational.com/resources/details/what-you-need-to-know-about-skin-grafts-and-donor-site-wounds [Accessed: 25 May 2021].

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