**8. Pathophysiology of burn wounds**

Systemic nature of the burn injury is unique that should be taken into consideration while approaching the patient. Understanding the pathophysiology of burn will provide useful information for early and effective management of burn patients, improve the quality of care for burn wounds, allow the identification of novel targets for the treatment of scar formation, and contribute to efforts to reduce the mortality. The local burn wound induces a generalized inflammatory response characterized by the activation of cytokines and release of various growth factors that can result in detrimental effects on many organs. The magnitude of this response depends on the severity of burn [1, 3, 5, 14, 15]. One of the distinct features of burn injury is that the cytokine-mediated signaling triggered by the tissue damage results in a generalized increase in capillary permeability and extravasation of plasma causing exaggerated edema response even at distant sites [3, 15]. Loss of intravascular fluid is accompanied by a decrease in cardiac output and increase in peripheral vascular resistance that may lead to hypoperfusion of organs and burn shock [1, 3, 15]. Hypercoagulability may occur due to systemic activation of platelet aggregation and fibrinolysis [1]. After the edema phase, a hypermetabolic state ensues which is characterized by an increase in oxygen consumption, marked protein and lipid catabolism, increase in energy requirements, high cardiac output, tachycardia, severe muscle weakness, cachexia, and decrease in immune functions [3, 15, 16].

**10. Evaluation of the severity of burn and referral of the patient**

(BI)" and "prognostic burn index (PBI)" [11].

the calculation of TBSA [11, 12].

according to the depth of injury:

with scarring.

at outpatient clinics [3, 11, 12].

Assessing the severity of burn injury is important in deciding the need for hospitalization. To assess the severity of damage, special indexes have been described including "Burn Index

Introductory Chapter: An Introduction to Burn Injuries http://dx.doi.org/10.5772/intechopen.71973 7

To assess the extent of burned area, several methods can be used including rule of nines, rule of fives, and Lund-Browder Chart. Lund-Browder Chart is especially used for children which more accurately estimates the age-specific percentage of TBSA [11, 12, 15]. Additionally, for local assessments of small burns, the palm method (palm with fingers accounts for 1% of total body surface area) can be used practically in adults. First-degree burns are not considered in

Although more precise methods including laser Doppler flowmetry and video microscopy have been defined, the depth of burn is mostly estimated clinically (the presence of pain or blister, appearance and color of the skin) in practice [11, 15]. Burns can be classified into three types

(a) **First degree (superficial):** Only the epidermis is involved. The skin is red and painful. There is usually no blistering and skin will blanch when touched. It heals without scarring.

(b) **Second degree (partial thickness):** In superficial dermal burns (SDB), only the papillary dermis is involved. In this case the skin is painful. Blisters are seen. When the bullae are deroofed, the skin is wet and blanches when touched. It heals with minimal pigmentary changes without hypertrophic scarring. If the reticular dermis is involved, it is considered as deep dermal burn (DDB). In this case, there is less pain and no bullae or blistering. There is eschar and the skin is white or yellow. It does not blanch on pressure. It heals

(c) **Third degree (full thickness):** There is little or no pain. It involves the epidermis and dermis and extends to the subcutaneous layer. The skin is leathery, dark, and inelastic. There is eschar. It does not blanch. It does not heal spontaneously, results in hypertrophic scar

Fourth-degree burns involve deeper structures including the subcutaneous tissue, muscle, tendons, ligaments, and bone. There is gangrene of tissue and carbonized appearance [12].

After the prehospital stabilization of the patient, depending on the severity of injury, treatment in a more equipped hospital may be required [11, 12]. The referral criteria may vary across different studies. To explain roughly, while major burns must be managed in hospitals with multidisciplinary burn teams, moderate burns can be managed in minor hospitals. No matter the extent, chemical burns, burns due to lighting strike, burns during pregnancy, and burns with suspicion of child abuse must be hospitalized. On the other hand, minor burns can be treated

Pain management is important in burn patients since the discomfort from pain results in anxiety, increases the risk of prolonged hospitalization, leads to loss of patient confidence, and

and contractures, and requires grafting [3, 11, 12].

Although the wound healing phases are similar to other types of wounds, the prolonged healing time is especially important in burn wounds [1–3]. The severity of burn, the mechanism of injury, and associated diseases of patients influence the wound healing [1]. Inflammatory phase includes the vasodilation and inflammatory cell migration through the cytokine signaling cascade. In proliferative phase, epithelization takes place by the migration of keratinocytes from the epithelium of the wound edges and dermal appendages. Remodeling (maturation) phase is characterized by the deposition of collagen by myofibroblasts, compaction of the connective tissue, and finally the contraction of the wound. Although the wound contraction and scar formation are normal and necessary for the closure of wound, excessive fibrosis and increased tensile stress during remodeling carry the risk of abnormal scar formation. Intense and prolonged inflammatory response with increased release of cytokines, growth factors, and other mediators from the inflammatory cells and platelets are associated with scar formation. The depth of burn, age of the patient, the treatment, and response of wound are important determinants for the development of scar tissue. Wounds that are not healed in 2–3 weeks are generally at risk of developing aberrant scar tissue [1–3].

Superficial burn wounds heal completely in 5–7 days during the proliferative phase. As the required dermal components are lost in deep burns, proliferation cannot be provided, and the epithelialization is delayed. The lack of supportive and vascular tissue is associated with abnormal contraction, and these wounds heal with hypertrophic scarring and contractures if left to heal spontaneously [1–3].
