Effect of Ambient Temperature on Metabolic Rate After Thermal Injury

Abstract

ObjectiveThe authors describe the effect of ambient temperature on metabolic rate after thermal injury. Summary Background DataThermal injury induces a hypermetabolic state, which is reported to increase with the extent of burn. The magnitude of this response is further influenced by ambient temperature. MethodsThe resting energy expenditure was measured by indirect calorimetry at ambient temperatures of 22, 28, 32, and 35 C. It was indexed to a calculated basal metabolic rate in normal volunteers and adult patients with burns involving at least 20% of the total body surface area who had no evidence of systemic infection. These measurements were performed between postburn days 6 and 21. ResultsThe effect of ambient temperature on metabolic rate was measured in 44 buvrn patients and 8 normal volunteers. Burn size ranged from 20 to 97% total body surface area with a mean of 44 + 18.5% total body surface area. Metabolic rate did not change significantly in control subjects as ambient temperature was varied (p < 0.05). Regression analysis showed that burn size and ambient temperature were significant determinants (p < 0.01) of metabolic rate in the patients and that together these factors accounted for 55% of the variation observed (df adj. r2 = 0.55) across the range of ambient temperatures studied. Metabolic rate was independent of burn size at ambient temperatures of 32 and 35 C (p < 0.02) and increased by a factor of 1.5 X basal metabolic rate. A further increase in metabolic rate, which was positively correlated with burn size, resulted from nonshivering thermogenesis at ambient temperatures 28 and 22 C. The magnitude of this response was greatest at 22 C. ConclusionsThese findings suggest that the hypermetabolic response to thermal injury is maximal in burns as small as 20% total body surface area and that an additional burn size-dependent increase in metabolic rate results from heat loss at ambient temperatures below thermoneutrality. 406

Accuracy of predictive methods to estimate resting energy expenditure of thermally‐injured patients

“…51,52 Patients in our study were kept at a mean ambient temperature of 23.3°C, which was similar to ambient temperatures reported by others. 39,47 Because the majority of the patients (n = 20, or 83% of the population) had 20% to 50% BSAB and their wounds were covered, it is unlikely that ambient temperature had a profound confounding effect on our measurements.…”

β‐Adrenergic blockade does not impair the skin blood flow sensitivity to local heating in burned and nonburned skin under neutral and hot environments in children

“…Under cool conditions, depending on degree burned, heat dissipation increases due to the removal of the epidermis, dermis, and subcutaneous tissue, prompting an increase in energy expenditure. In this context, metabolic rates and catecholamines are found to be reduced in warm conditions (32–35°C) when ambient temperature matches internal body temperature (minimizing heat exchange) while being elevated in neutral cool environments (22°C; increasing the gradient heat exchange) [4,30,56,57]. Our finding related to resting skin blood flow are in agreement with this as we found that in a neutral environment, skin blood flow in both burned and unburned skin are significantly elevated by 40–60% of maximal capacity compared to non-burned healthy children skin, which is at about 10% SkBF max (Figure 1).…”

Admission Temperature and Survival in Patients Admitted to Burn Centers

“…It has been shown that severely burned patients have difficulty maintaining normothermia during the hypermetabolic phase. 2 However, there is little direct evidence in patients supporting the maintenance of normothermia during the initial resuscitation.…”