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

Current understanding of thermo(dys)regulation in severe burn injury and the pathophysiological influence of hypermetabolism, adrenergic stress and hypothalamic regulation—a systematic review

Background

In this systematic review, we summarize the aetiology as well as the current knowledge regarding thermo(dys)regulation and hypothermia after severe burn trauma and aim to present key concepts of pathophysiology and treatment options. Severe burn injuries with >20% total body surface area (TBSA) affected commonly leave the patient requiring several surgical procedures, prolonged hospital stays and cause substantial changes to body composition and metabolism in the acute and long-term phase. Particularly in severely burned patients, the loss of intact skin and the dysregulation of peripheral and central thermoregulatory processes may lead to substantial complications.

Methods

A systematic and protocol-based search for suitable publications was conducted following the PRISMA guidelines. Articles were screened and included if deemed eligible. This encompasses animal-based in vivo studies as well as clinical studies examining the control-loops of thermoregulation and metabolic stability within burn patients

Results

Both experimental animal studies and clinical studies examining thermoregulation and metabolic functions within burn patients have produced a general understanding of core concepts which are, nonetheless, lacking in detail. We describe the wide range of pathophysiological alterations observed after severe burn trauma and highlight the association between thermoregulation and hypermetabolism as well as the interactions between nearly all organ systems. Lastly, the current clinical standards of mitigating the negative effects of thermodysregulation and hypothermia are summarized, as a comprehensive understanding and implementation of the key concepts is critical for patient survival and long-term well-being.

Conclusions

The available in vivo animal models have provided many insights into the interwoven pathophysiology of severe burn injury, especially concerning thermoregulation. We offer an outlook on concepts of altered central thermoregulation from non-burn research as potential areas of future research interest and aim to provide an overview of the clinical implications of temperature management in burn patients.

Resting β-Adrenergic Blockade Does Not Alter Exercise Thermoregulation in Children With Burn Injury: A Randomized Control Trial

The objective of this study was to test the hypothesis that propranolol, a commonly prescribed β-blocker to burned children, in combination with exercise-heat stress, increases the risk of heat illness and exercise intolerance. In a randomized double-blind study, propranolol was given to 10 burned children, and placebo was given to 10 additional burned children (matched for TBSA burned; mean ± SD, 62 ± 13%), while nonburned children served as healthy controls. All groups were matched for age and body morphology (11.2 ± 3.0 years; 146 ± 19 cm; 45 ± 18 kg; 1.3 ± 0.4 m2). All children exercised in hot conditions (34.3 ± 1.0°C; 26 ± 2% relative humidity) at 75% of their peak aerobic capacity. At the end of exercise, none of the groups differed for final or change from baseline intestinal temperature (38.0 ± 0.5°C; 0.02 ± 0.01Δ°C·min-1), unburned (37.0 ± 0.6°C) and burned skin temperatures (36.9 ± 0.7°C; nonburn group excluded), heat loss (21 ± 18 W m-2), whole-body thermal conductance (118 ± 113 W m-2), or physiological strain index (5.6 ± 1). However, burn children exercised less than nonburn group (21.2 ± 8.6 vs 30 ± 0.0 min; P < .001) and had a lower calculated exercise tolerance index (1.0 ± 0.0 vs 6.7 ± 4.3; P < .01). Burned children had lower peak heart rates than nonburned children (173 ± 13 vs 189 ± 7 bpm; P < .01), with greater relative cardiac work rates at the end of exercise (97 ± 10 vs 85 ± 11% peak heart rate; P < .01). Resting β-adrenergic blockade does not affect internal body temperature of burned children exercising at similar relative intensities as nonburn children in the heat. Independent of propranolol, a suppressed cardiac function may be associated to exercise intolerance in children with severe burn injury.

Effects of Drugs and Excipients on Hydration Status

Despite being the most essential nutrient, water is commonly forgotten in the fields of pharmacy and nutrition. Hydration status is determined by water balance (the difference between water input and output). Hypohydration or negative water balance is affected by numerous factors, either internal (i.e., a lack of thirst sensation) or external (e.g., polypharmacy or chronic consumption of certain drugs). However, to date, research on the interaction between hydration status and drugs/excipients has been scarce. Drugs may trigger the appearance of hypohydration by means of the increase of water elimination through either diarrhea, urine or sweat; a decrease in thirst sensation or appetite; or the alteration of central thermoregulation. On the other hand, pharmaceutical excipients induce alterations in hydration status by decreasing the gastrointestinal transit time or increasing the gastrointestinal tract rate or intestinal permeability. In the present review, we evaluate studies that focus on the effects of drugs/excipients on hydration status. These studies support the aim of monitoring the hydration status in patients, mainly in those population segments with a higher risk, to avoid complications and associated pathologies, which are key axes in both pharmaceutical care and the field of nutrition.

Burn Injury May Have Age-Dependent Effects on Strength and Aerobic Exercise Capacity in Males

Whether burn injury affects boys and men differently is currently unknown. To test the hypothesis that burned boys have lower exercise capacity and exercise training-induced responses compared with burned men, 40 young boys (12 ± 4 years, 149 ± 20 cm, 46 ± 18 kg) were matched to 35 adult men (33 ± 9 years, 174 ± 10 cm, 84 ± 16 kg) based on extent of burn injury (total body surface area burned, boys 46 ± 14% vs men 47 ± 30, P = .85) and length of hospital stay (boys 33 ± 23 vs men 41 ± 32 days, P = .23). Strength (peak torque) and cardiorespiratory fitness (peak VO2) were normalized to kg of lean body mass for group comparisons. Each group was also compared with normative age-sex matched values at discharge and after an aerobic and resistance exercise training (RET) program. A two-way factorial analysis of covariance assessed interaction and main effects of group and time. We found that boys and men showed similar pre-RET to post-RET increases in total lean (~4%) and fat (7%) mass (each P ≤ .008). Both groups had lower age-sex matched norm values at discharge for peak torque (boys 36%; men 51% of normative values) and peak VO2 (boys: 44; men: 59%; each P ≤ .0001). Boys strength were 13-15 per cent lower than men at discharge and after RET (main effect for group, P < .0001). Cardiorespiratory fitness improved to a greater extent in men (19%) compared with boys (10%) after the RET (group × time interaction, P = .011). These results show that at discharge and after RET, burn injury may have age-dependent effects and should be considered when evaluating efficacy and progress of the exercise program.

Children with Burn Injury Have Impaired Cardiac Output during Submaximal Exercise

INTRODUCTION

Burn trauma damages resting cardiac function; however, it is currently unknown if the cardiovascular response to exercise is likewise impaired. We tested the hypothesis that, in children, burn injury lowers cardiac output (Q˙) and stroke volume (SV) during submaximal exercise.

METHODS

Five children with 49% ± 4% total body surface area (BSA) burned (two female, 11.7 ± 1 yr, 40.4 ± 18 kg, 141.1 ± 9 cm) and eight similar nonburned controls (five female, 12.5 ± 2 yr, 58.0 ± 17 kg, 147.3 ± 12 cm) with comparable exercise capacity (peak oxygen consumption [peak V˙O2]: 31.9 ± 11 vs 36.8 ± 8 mL O2·kg·min, P = 0.39) participated. The exercise protocol entailed a preexercise (pre-EX) rest period followed by 3-min exercise stages at 20 W and 50 W. V˙O2, HR, Q˙ (via nonrebreathing), SV (Q˙/HR), and arteriovenous O2 difference ([a-v]O2diff, Q˙/ V˙O2) were the primary outcome variables.

RESULTS

Using a 2-way factorial ANOVA (group [G] × exercise [EX]), we found that Q˙ was approximately 27% lower in the burned than the nonburned group at 20 W of exercise (burned 5.7 ± 1.0 vs nonburned: 7.9 ± 1.8 L·min) and 50 W of exercise (burned 6.9 ± 1.6 vs nonburned 9.2 ± 3.2 L·min) (G-EX interaction, P = 0.012). SV did not change from rest to exercise in burned children but increased by approximately 24% in the nonburned group (main effect for EX, P = 0.046). Neither [a-v] O2diff nor V˙O2 differed between groups at rest or exercise, but HR response to exercise was reduced in the burn group (G-EX interaction, P = 0.004). When normalized to BSA, SV (index) was similar between groups; however, Q˙ (index) remained attenuated in the burned group (G-EX interaction, P < 0.008).

CONCLUSIONS

Burned children have an attenuated cardiovascular response to submaximal exercise. Further investigation of hemodynamic function during exercise will provide insights important for cardiovascular rehabilitation in burned children.