Body temperature in major burn patient

The loss of the surface of the skin by a burn leads directly to the loss of its functions resulting in an alteration in thermoregulation, alteration of sweat regulation (heat losses by evaporation) and alteration of the regulation of blood flow (heat losses by radiation and convection) ⁸.

Heat losses of the burn patient are presented by conduction, convection, radiation and evaporation ⁽⁹. Control of driving losses shall be carried out by acting on the surface that is positioned to the patient either the transport table, bed or surgical table. Treatment on convection losses shall be performed by monitoring environmental temperature and humidity and protecting from air currents. Radiation losses will be losses to the environment, so the patient's body exposure should be limited. And in the face of evaporation losses, contact with wet dressings and sweat control ⁽⁹. Heating and temperature maintenance measures will be applied to alleviate these losses.

The loss of heat and water through the burn causes an increase in central temperature, reprogramming the hypothalamic regulation, so patients are expected to have a higher temperature of up to 2ºC without infectious focus being around 38,5ºC ¹⁰. A body temperature of less than 35ºC ¹¹ should be avoided because of its unwanted effects and despite not knowing the optimal target temperature, it should be greater than 37,5ºC ⁽⁴.

Own elaboration

Figure 1.  Heat loss of the burn patient. 

Hypothermia in burn patients may increase vasoconstriction lesions, cause clotting disturbances, decreased enzymatic activity, impaired breathing, may cause arrhythmias and death ^11,12,13. The centralized care offered in a large burn unit provides a controlled and standardized environment indispensable for the survival of these critical and immunocompromised patients ¹⁴.

Pre-hospital action and implementation of established recommendations for burn cooling, monitoring the risk of hypothermia and applying heat loss control measures, will determine the progression of hypothermia and the need for faster warming of patients with extensive burns ^3,6.

Once stabilized and for the first few hours after the injury, the patient will need to be covered with clean, dry blankets to prevent or limit hypothermia. Measures to maintain body temperature include occlusive dressing to prevent heat loss, local infection and promote healing. The barrier effect of dressings ensures thermal insulation and moisture maintenance, allowing gas exchange. Along with the limitation and control of body exposure, they are relevant factors to avoid decreased body temperature ¹².

It is called critical temperature, at the temperature that triggers a thermogenic cell response. As the severity of the burn increases, the critical temperature decreases. While the critical temperature and time to reach it may vary between patients, hypermetabolic response can be controlled by high ambient temperature, minimizing heat losses, improving coagulation and reducing morbidity and mortality ⁴.

The target temperature range of patients in a study in US burn units was between 36 - 38ºC ⁽¹⁵. Despite the absence of a clear definition of the target temperature, there is a relationship between higher body temperature and lower metabolic expenditure. shall be considered in the burn patient (Table 1).

Table 1.  Body temperature in major burn patients 

^*REE Resting Energy Expenditure

^**TBSA Total Burn Surface Area

In the care of the burn patient, it should be noted that the baseline temperature of these patients is 38.5ºC, and that a temperature below 37ºC can be considered as relatively hypothermia ⁽¹⁶.

Energy metabolism in burn patients

Two phases are considered in the metabolic response of the burn patient, the acute phase ranging from the accident to 72 hours, and the hypermetabolic phase. The hypermetabolic state developed by the burn patient after the acute phase increases energy consumption. Several actions are needed to decrease the effects of hypermetabolism to reduce caloric expenditure, at least so that there is no increase in metabolism ⁽¹⁷.

Burns greater than 20% TBSA will develop a hypermetabolic, inflammatory and stress response in a similar way to that developed with burns greater than 40% TBSA ¹⁸. It`s recommended to act on hypermetabolism, as its decrease will improve the healing of burns. The early and appropriate nutritional contribution to the patient will intervene on the catabolic state by decreasing energy demand ¹⁹.

During the acute phase after burning, the patient has a severe loss of lean body mass, free radical imbalance in relation to antioxidant defense mechanisms and impaired immune function. Intervention through adequate nutritional support and early onset of enteral nutrition will meet the energy demands of proteins, fats, lipids and micronutrients. In addition, the supplement of micronutrients such as glutamine, will contribute to the recovery of lean mass ⁽²⁰.

The metabolic expenditure of burned patients in the study of Stanojcic et al ¹⁸ was 1,4 ± 0,2 times the basal metabolic expenditure, while in the study of Leung et al ⁽²¹ was 1,43 ± 0,32 times the BMR in patients with burns less than 40%.

Water losses of up to 4 l/m2 of burn surface area per day are found ⁽²². The evaporation body fluid losses quantified are 3 to 4 times greater than in healthy skin depending on deep second-degree and third-degree burns. It can be assessed by the Trans Epidermal Water Loss index (TEWL), measuring the amount of water in grams that passes through the skin to the surrounding atmosphere, per hour and skin area, being according to the depth of the burn from 50 to 62 gr/m² per hour ⁽²³ (Table 2).

Table 2.  Thermoregulation in major burn patients 

^*REE Resting Energy Expenditure

^**TBSA Total Burn Surface Area

^***BMR Basal Metabolic Rate

Heating methods

Measures to alleviate heat losses should act in heating and maintaining the patient's body temperature through active internal heating methods such as intravenous hot liquid administration and other heating and extern methods that will be passive and/or active.

An analysis of the use of heating methods, in US burn units, declared in relation to total cases: 94.2% increase in ambient temperature, followed by 88.5% forced air appliances, 82.7% tempered intravenous liquids, 38.5% conductive heating pads and temperature-regulated intravascular catheter 21.6%¹⁵ (Table 3).

Table 3.  Environmental temperature in the care of major burn patients 

^*REE Metabolic Energy Expenditure

^**BMR Basal Metabolic Rate

^***TBSA Total Burn Surface Area

Passive external heating: Ambient temperature

As a passive external heating method a high ambient temperature is used, the recommendations place it between 28 and 33º ^11). This increase in ambient temperature can reduce Resting Energy Expenditure from 2.0 times to 1.4 times in patients with burns greater than 40% TBSA.

This measure serves to minimize the increase in basal metabolic rate caused by heat generation and water loss by evaporation. It is a Grade B recommendation of evidence by Joanna Briggs Institute ⁽²⁴ providing a warm room with an ambient temperature of 28-32ºC, to prevent hypothermia.

Pruskowski et al ⁽¹⁵ observed that the increase in ambient temperature was the most commonly used heating in burn units, using a wide temperature arc of 24 to 35ºC.

To decrease hypermetabolic response, such as non-pharmacological measures, it can be acted by raising the ambient temperature. Kelemen et al ⁽²⁵ found that the ambient temperature range from 30ºC to 32ºC would reduce hypermetabolism in patients with burns from 20% TBSA, reaching a 22% decrease in energy demand compared to an ambient temperature of 22ºC. Environmental temperatures above 32ºC would no longer provide this benefit. There is a relationship between higher burn body surface area and higher temperature demand ⁽²⁵.

Active external heating

Active external heating is obtained by directly applying heat to the surface of the body. The use of convective air as an active external heating method has been studied mainly in the surgical and care field of critical patients ⁽²⁶. This application is effective to achieve normothermia starting from a body temperature of 32ºC. The application of convective air achieves a higher rate of 1ºC of heating compared to other methods ⁽²⁷.