Understanding metabolic function after non-severe burn injuries in adults

Tyler J Osborne

Burns are more than skin deep. We know now that non-severe burns have measurable systemic impacts, specifically impairing metabolic function, and potentially accelerates the onset of diseases of metabolism and ageing. This impaired metabolic function is characterised by an elevated metabolic state, with resting energy expenditure (REE) peaking at ~40 to 80% above age predicted levels for at least 3 years post-burn. However metabolic impairment has predominantly been studied in people with severe burns (covering > 20% total body surface area, TBSA). Emerging research has suggested that non-severe burns (≤20% TBSA) elicit similar impairments to metabolic function and account for ~93% of burns presenting at hospital units. Despite the high prevalence, it is still largely unknown how metabolism changes in non-severely burned patients the weeks, months and year after injury. Therefore, the purpose of this thesis presents an account of the research program aimed to improve our understanding of three key aspects of impaired metabolic function in non-severely burned patients: i) increased resting energy expenditure; ii) altered carbohydrate metabolism; and ii) increased metabolism-related inflammatory markers. A review of the literature (Chapter 2) describes the current understanding and knowledge gaps in the understanding of metabolic function in burned patients and common therapeutic approaches to reduce metabolic impairment. I also propose a novel framework to assess carbohydrate metabolism post-burn using indirect calorimetry, the current gold-standard for assessing metabolism. In Chapter 3, I show that none of the eight predictive equations that clinicians use to guide energy intake post non-severe burn accurately estimate resting energy expenditure compared to indirect calorimetry. I also show that REE is greater than age-, sex-, and stature-matched predictive values in this cohort of non-severely burned patients. Moreover, cross sectional analysis of 45 non-severely burned participants provides evidence that REE may remain above normative levels for years after the injury (Chapter 4) In Chapter 5, I implemented the novel framework presented in Chapter 2 to assess metabolic flexibility in nine non-severely burned patients and eight age- and sex-matched controls. I found that, while fasted, the non-severely burned patients had elevated resting carbohydrate metabolism compared to the control cohort. In Chapter 6, I demonstrate that a six-week, strength and aerobic exercise intervention was safe, well-adhered to and beneficial for non-severely burned patients (injured > 1 year ago). However, the intervention elicited no changes to pro-inflammatory markers or glucose metabolism. The cumulative findings of this thesis were subsequently used to develop a randomised controlled trial protocol (Chapter 7) for a 12-month exercise and diet intervention to improve metabolic function, namely glycaemic control measured by HbA1c, in non-severely burned patients. In sum, this PhD highlights novel approaches to examining metabolic function after burn injury and provides important evidence for adapting exercise and dietary intervention to improve metabolic function and reduce the likelihood of developing type 2 diabetes in non-severely burned patients.

Understanding metabolic function after non-severe burn injuries in adults

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