Resting ß-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 ß-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 ß-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.

ß-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.

OBJECTIVE: We tested the hypothesis that propranolol, a drug given to burn patients to reduce hypermetabolism/cardiac stress, may inhibit heat dissipation by changing the sensitivity of skin blood flow (SkBF) to local heating under neutral and hot conditions. METHODS: In a randomized double-blind study, a placebo was given to eight burned children, while propranolol was given to 13 burned children with similar characteristics (mean±SD: 11.9±3 years, 147±20 cm, 45±23 kg, 56±12% Total body surface area burned). Nonburned children (n=13, 11.4±3 years, 152±15 cm, 52±13 kg) served as healthy controls. A progressive local heating protocol characterized SkBF responses in burned and unburned skin and nonburned control skin under the two environmental conditions (23 and 34°C) via laser Doppler flowmetry. RESULTS: Resting SkBF was greater in burned and unburned skin compared to the nonburned control (main effect: skin, P<.0001; 57±32 burned; 38±36 unburned vs 9±8 control %SkBFmax ). No difference was found for maximal SkBF capacity to local heating between groups. Additionally, dose-response curves for the sensitivity of SkBF to local heating were not different among burned or unburned skin, and nonburned control skin (EC50 , P>.05) under either condition. CONCLUSION: Therapeutic propranolol does not negatively affect SkBF under neutral or hot environmental conditions and further compromise temperature regulation in burned children.

The effect of exercise training with an additional inspiratory load on inspiratory muscle fatigue and time-trial performance.

The purpose was to determine the effect of moderate-intensity exercise training (ET) on inspiratory muscle fatigue (IMF) and if an additional inspiratory load during ET (ET+IL) would further improve inspiratory muscle strength, IMF, and time-trial performance. 15 subjects were randomly divided to ET (n=8) and ET+IL groups (n=7). All subjects completed six weeks of exercise training three days/week at ∼70%V̇O2peak for 30min. The ET+IL group breathed through an inspiratory muscle trainer (15% PImax) during exercise. 5-mile, and 30-min time-trials were performed pre-training, weeks three and six. Inspiratory muscle strength increased (p<0.05) for both groups to a similar (p>0.05) extent. ET and ET+IL groups improved (p<0.05) 5-mile time-trial performance (∼10% and ∼18%) and the ET+IL group was significantly faster than ET at week 6. ET and ET+IL groups experienced less (p<0.05) IMF compared to pre-training following the 5-mile time-trial. In conclusion, these data suggest ET leads to less IMF, ET+IL improves inspiratory muscle strength and IMF, but not different than ET alone.

Emergency Incident Rehabilitation: Resource Document to the Position Statement of the National Association of EMS Physicians.

Position Statement: Emergency Incident Rehabilitation The National Association of EMS Physicians® believes that: Emergency operations and training conducted while wearing protective clothing and respirators is physiologically and cognitively demanding. The heat stress and fatigue created by working in protective clothing and respirators creates additional risk of illness/injury for the public safety provider. Emergency incident rehabilitation provides a structured rest period for rehydration and correction of abnormal body core temperature following work in protective clothing and respirators. Emergency incident rehab should be conducted at incidents (e.g. fireground, hazardous materials, and heavy rescue emergencies) and trainings involving activities that may lead to exceeding safe levels of physical and mental exertion. Emergency incident rehabilitation is incident care, not fitness for duty, and meant to reduce physiologic strain and prepare the responder to return to duty at the current incident and for the remainder of the shift. EMS should play a role in emergency incident rehabilitation with providers trained to understand the physiologic response of healthy individuals to environmental, exertional, and cognitive stress and implement appropriate mitigation strategies. An appropriately qualified physician should have oversight over the creation and implementation of emergency incident rehabilitation protocols and may be separate from the roles and responsibilities of the occupational medicine physician. There are no peer-reviewed data related to cold weather rehabilitation. Future studies should address this limitation to the literature.

Pilot Study Examining the Effects of Atropine on Performance during Uncompensable Heat Stress.

UNLABELLED: In many operational scenarios, hypohydration can be corrected with oral rehydration following the work interval. Although rare, there are potential situations that require extended intervals of uncompensable heat stress exposure while working in personal protective equipment (PPE). Under these conditions, retention of body water may be valuable to preserve work capacity and reduce cardiovascular strain. We conducted a pilot study comparing intramuscular atropine sulfate versus saline placebo to establish the safety profile of the protocol and to provide pilot data for future investigations. Five, healthy, heat-acclimated subjects completed this crossover design laboratory study. Each subject performed up to one hour of exertion in a hot environment while wearing a chemical resistant coverall. Atropine sulfate (0.02 mg/kg) or an equivalent volume of sterile saline was administered by intramuscular injection. Core temperature, heart rate, perceptual measures, and changes in body mass were measured. All five subjects completed the acclimation period and both protocols. No adverse events occurred, and no pharmacologically induced delirium was identified. Change in body mass was less following exercise influenced by atropine sulfate (p = 0.002). Exertion time tended to be longer in the atropine sulfate arm (p = 0.08). Other measures appeared similar between groups. Intramuscular atropine sulfate reduced sweating and tended to increase the work interval under uncompensable heat stress when compared to saline placebo. Heart rate and temperature changes during exertion were similar in both conditions suggesting that the influence of an anticholinergic agent on thermoregulation may be minimal during uncompensable heat stress. KEY WORDS: thermoregulation; cholinolytic; anticholinergic; reaction time.

Effects of Low-Dose Aspirin Therapy on Thermoregulation in Firefighters.

BACKGROUND: Heart attack is the most common cause of line-of-duty death in the fire service. Daily aspirin therapy is a preventative measure used to reduce the morbidity of heart attacks but may decrease the ability to dissipate heat by reducing skin blood flow. METHODS: In this double-blind, placebo-controlled, crossover study, firefighters were randomized to receive 14 days of therapy (81-mg aspirin or placebo) before performing treadmill exercise in thermal-protective clothing in a hot room [38.8 ± 2.1°C, 24.9 ± 9.1% relative humidity (RH)]. Three weeks without therapy was provided before crossing to the other arm. Firefighters completed a baseline skin blood-flow assessment via laser Doppler flowmetry; skin was heated to 44°C to achieve maximal cutaneous vasodilation. Skin blood flow was measured before and after exercise in a hot room, and at 0 minutes, 10 minutes, 20 minutes, and 30 minutes of recovery under temperature conditions (25.3 ± 1.2°C, 40.3 ± 13.7% RH). Platelet clotting time was assessed before drug administration, and before and after exercise. RESULTS: Fifteen firefighters completed the study. Aspirin increased clotting time before and after exercise compared with placebo (p = 0.003). There were no differences in absolute skin blood flow between groups (p = 0.35). Following exercise, cutaneous vascular conductance (CVC) was 85 ± 42% of maximum in the aspirin and 76 ± 37% in the placebo groups. The percentage of maximal CVC did not differ by treatment before or after recovery. Neither maximal core body temperature nor heart rate responses to exercise differed between trials. CONCLUSION: There were no differences in skin blood flow during uncompensable heat stress following exercise after aspirin or placebo therapy.

Characterization of electrocardiogram changes throughout a marathon.

PURPOSE: There are few data examining cardiovascular physiology throughout a marathon. This study was devised to characterize electrocardiographic activity continuously throughout a marathon. METHODS: Cardiac activity was recorded from 19 subjects wearing a Holter monitor during a marathon. The 19 subjects (14 men and 5 women) were aged 39 ± 16 years (mean ± SD) and completed a marathon in 4:32:16 ± 1:23:35. Heart rate (HR), heart rate variability (HRV), T-wave amplitude, T-wave amplitude variability, and T-wave alternans (TWA) were evaluated continuously throughout the marathon. RESULTS: Averaged across all subjects, HRV, T-wave amplitude variability, and TWA increased throughout the marathon. Increased variability in T-wave amplitude occurred in 86 % of subjects, characterized by complex oscillatory patterns and TWA. Three min after the marathon, HR was elevated and HRV was suppressed relative to the pre-marathon state. CONCLUSION: HRV and T-wave amplitude variability, especially in the form of TWA, increase throughout a marathon. Increasing TWA as a marathon progresses likely represents a physiologic process as no arrhythmias or cardiac events were observed.

A randomized controlled trial of aspirin and exertional heat stress activation of platelets in firefighters during exertion in thermal protective clothing.

PURPOSE: Platelet aggregation is enhanced in firefighters following short bouts of work in thermal protective clothing (TPC). We sought to determine if aspirin therapy before and/or following exertion in TPC prevents platelet activation. METHODS: In a double-blind, placebo-controlled study, 102 firefighters were randomized to receive daily therapy (81 mg aspirin or placebo) for 14 days before and a single dose (325 mg aspirin or placebo) following exercise in TPC resulting in four potential assignments: aspirin before and after exercise (AA), placebo before and after exercise (PP), aspirin before and placebo after exercise (AP), and placebo before and aspirin after exercise (PA). Platelet closure time (PCT) was measured with a platelet function analyzer before the 2-week treatment, after the 2 week treatment period, immediately after exercise, and 30, 60, and 90 minutes later. RESULTS: Baseline PCT did not differ between groups. PCT changed over time in all four groups (p < 0.001) rising to a median of >300 seconds [IQR 99, 300] in AA and >300 [92, 300] in AP prior to exercise. Following exercise, median PCT decreased to in all groups. Median PCT returned to >300 seconds 30 minutes later in AA and AP and rose to 300 seconds in PA 60 minutes after exercise. CONCLUSIONS: Daily aspirin therapy blunts platelet activation during exertional heat stress and single-dose aspirin therapy following exertional heat stress reduces platelet activation within 60 minutes.

Risk factors for hypothermia in EMS-treated burn patients.

OBJECTIVE: Hypothermia has been associated with increased mortality in burn patients. We sought to characterize the body temperature of burn patients transported directly to a burn center by emergency medical services (EMS) personnel and identify the factors independently associated with hypothermia. METHODS: We utilized prospective data collected by a statewide trauma registry to carry out a nested case-control study of burn patients transported by EMS directly to an accredited burn center between 2000 and 2011. Temperature at hospital admission ≤36.5°C was defined as hypothermia. We utilized registry data abstracted from prehospital care reports and hospital records in building a multivariable regression model to identify the factors associated with hypothermia. RESULTS: Forty-two percent of the sample was hypothermic. Burns of 20-39% total body surface area (TBSA) (OR 1.44; 1.17-1.79) and ≥40% TBSA (OR 2.39; 1.57-3.64) were associated with hypothermia. Hypothermia was also associated with age > 60 (OR 1.50; 1.30-1.74), polytrauma (OR 1.58; 1.19-2.09), prehospital Glasgow Coma Scale <8 (OR 2.01; 1.46-2.78), and extrication (OR 1.49; 1.30-1.71). Hypothermia was also more common in the winter months (OR 1.54; 1.33-1.79) and less prevalent in patients weighing over 90 kg (OR 0.63; 0.46-0.88). CONCLUSIONS: A substantial proportion of burn patients demonstrate hypothermia at hospital arrival. Risk factors for hypothermia are readily identifiable by prehospital providers. Maintenance of normothermia should be stressed during prehospital care.

Admission temperature and survival in patients admitted to burn centers.

It is commonly believed that hypothermia occurring during burn resuscitation is associated with poor outcome, but there is little direct supporting evidence. The authors conducted an analysis of a statewide trauma registry to determine whether hypothermia (T ≤36.5°C) was associated with mortality when controlling for clinical confounders. They included all patients treated at an accredited burn center from 2000 to 2011 where the trauma registrar recorded the primary injury type as a burn. They excluded records with missing data and nonphysiologic temperature (<26°C or >42°C). The primary exposure of interest was hypothermia. The authors constructed a hierarchical, multivariable logistic regression model to examine the effect of hypothermia on survival, controlling for potentially confounding variables. Predictors of mortality are presented as odds ratio (95% confidence interval). Primary burn injury was coded 17,098 times during the study period. Of these, 3809 were not treated at a burn center and 1192 were excluded for missing data. Admission hypothermia was independently associated with mortality (1.91 [1.58-2.29]) when adjusting for age, sex, total second- and third-degree burn surface area (TBSA), comorbid conditions, injury severity score, direct transport vs referral, method of temperature measurement, year, and the hospital providing care. Increasing age, female sex, TBSA >40%, presence of multiple comorbid conditions, and increasing injury severity score were associated with mortality. Other variables in the model were not independently associated with outcome. There was a weak correlation between TBSA and admission temperature (r = .18). Hypothermia at hospital admission is independently associated with mortality in burn patients when controlling for clinical confounders. Future studies should address potential causes underlying this observation.

Mitigation and prevention of exertional heat stress in firefighters: a review of cooling strategies for structural firefighting and hazardous materials responders.

Most duties performed by firefighters require the use of personal protective equipment, which inhibits normal thermoregulation during exertion, creating an uncompensable heat stress. Structured rest periods are required to correct the effects of uncompensable heat stress and ensure that firefighter safety is maintained and that operations can be continued until their conclusion. While considerable work has been done to optimize firefighter cooling during fireground operations, there is little consensus on when or how cooling should be deployed. A systematic review of cooling techniques and practices among firefighters and hazardous materials operators was conducted to describe the state of the science and provide recommendations for deploying resources for fireground rehab (i.e., structured rest periods during an incident). Five electronic databases were searched using a selected combination of key words. One hundred forty publications were found in the initial search, with 27 meeting all the inclusion criteria. Two independent reviewers performed a qualitative assessment of each article based on nine specific questions. From the selected literature, the efficacy of multiple cooling strategies was compared during exertion and immediately following exertion under varying environmental conditions. When considering the literature available for cooling firefighters and hazardous materials technicians during emergency incident rehabilitation, widespread use of cooling devices does not appear to be warranted if ambient temperature and humidity approximate room temperature and protective garments can be removed. When emergency incident rehabilitation must be conducted in hot or humid conditions, active cooling devices are needed. Hand/forearm immersion is likely the best modality for cooling during rehab under hot, humid conditions; however, this therapy has a number of limitations. Cooling during work thus far has been limited primarily to cooling vests and liquid- or air-cooled suits. In general, liquid-perfused suits appear to be superior to air-cooled garments, but both add weight to the firefighter, making current iterations less desirable. There is still considerable work to be done to determine the optimal cooling strategies for firefighters and hazardous materials operators during work.

Effects of a hospital based Wellness and Exercise program on quality of life of children with severe burns.

OBJECTIVE: To examine the effect of a 12-week Wellness and Exercise (W&E) program on the quality of life of pediatric burn survivors with burns of ≥40% total body surface area. We hypothesized this comprehensive regimen would improve physical and psychosocial outcomes. METHODS: Children were recruited for participation upon their discharge from the ICU. They were not taking anabolic/cardiovascular agents. Seventeen children participated in the W&E group and 14 children in the Standard of Care (SOC) group. Quality of life was assessed with the Child Health Questionnaire (CHQ) at discharge and 3 months. Children completed the CHQ-CF 87 and caregivers completed the CHQ-PF 28. RESULTS: The mean age of children in the W&E group was 14.07±3.5 years and mean TBSA was 58±11.8%. The mean age of children in the SOC group was 13.9±3.1 years and mean TBSA was 49±7.8%. ANOVA did not reveal statistically significant differences between the groups. Matched paired t-tests revealed that parents with children in the W&E group reported significant improvements with their children's physical functioning, role/social physical functioning, mental health, overall physical and psychosocial functioning after exercise. CONCLUSIONS: These results are clinically relevant in that a comprehensive W&E program may be beneficial in promoting physical and psychosocial outcomes.

Temperature responses in severely burned children during exercise in a hot environment.

The authors have previously described thermoregulatory responses of severely burned children during submaximal exercise in a thermoneutral environment. However, the thermoregulatory response of burned children to exercise in the heat is not well understood and could have important safety implications for rehabilitation. Children (n = 10) with >40% TBSA burns and nonburned children (n = 10) performed a 30-minute bout of treadmill exercise at 75% of their peak aerobic power in a heated environment. Intestinal temperature, burned and unburned skin temperature, and heart rate were recorded pre-exercise, every 2 minutes during exercise, and during recovery. Three of the 10 burned children completed the exercise bout in the heat; however, all the nonburned children completed the 30-minute bout. One burned child reached a core body temperature >39 degrees C at minute 23. Burned children had significantly higher core body temperature through the first 12 minutes of exercise compared with nonburned children. However, nine of 10 (90%) burned children did not become hyperthermic during exercise in the heat. Specific to this study, hyperthermia did not typically occur in burned children, relative to nonburned children. Whether this is due to an intolerance to exercise in the heat or to an inability to generate sufficient heat during exercise needs to be explored further.

Whole body protein kinetics measured with a non-invasive method in severely burned children.

UNLABELLED: Persistent and extensive skeletal muscle catabolism is characteristic of severe burns. Whole body protein metabolism, an important component of this process, has not been measured in burned children during the long-term convalescent period. The aim of this study was to measure whole body protein turnover in burned children at discharge (95% healed) and in healthy controls by a non-invasive stable isotope method. Nine burned children (7 boys, 2 girls; 54±14 (S.D.)% total body area burned; 13±4 years; 45±20 kg; 154±14 cm) and 12 healthy children (8 boys, 4 girls; 12±3 years; 54±16 kg; 150±22 cm) were studied. A single oral dose of (15)N-alanine (16 mg/kg) was given, and thereafter urine was collected for 34 h. Whole body protein flux was calculated from labeling of urinary urea nitrogen. Then, protein synthesis was calculated as protein flux minus excretion, and protein breakdown as flux minus intake. At discharge, total protein turnover was 4.53±0.65 (S.E.)g kg body weight(-1) day(-1) in the burned children compared to 3.20±0.22 g kg(-1) day(-1) in controls (P=0.02). Expressed relative to lean body mass (LBM), the rates were 6.12±0.94 vs. 4.60±0.36 g kg LBM(-1) day(-1) in burn vs. healthy (P=0.06). Total protein synthesis was also elevated in burned vs. healthy children, and a tendency for elevated protein breakdown was observed. CONCLUSION: Total protein turnover is elevated in burned children at discharge compared to age-matched controls, possibly reflecting the continued stress response to severe burn. The oral (15)N-alanine bolus method is a convenient, non-invasive, and no-risk method for measurement of total body protein turnover.

Absence of exertional hyperthermia in a 17-year-old boy with severe burns.

An important safety concern when exercising burned patients is the potential for an excessive increase in core body temperature (hyperthermia=body core temperature>39 degrees C) during exercise. We examined the thermoregulatory response to exercise in the heat (31 degrees C, relative humidity 40%) in a 17-year-old boy with a 99% TBSA burn. A 30-minute exercise test was performed at an intensity of 75% of his peak aerobic capacity. Intestinal temperature was assessed via telemetry with an ingestible capsule. Intestinal temperature was measured before, during, and postexercise. The patient completed 12 minutes of the 30-minute exercise test. Starting core temperature was 36.98 degrees C and increased 0.69 degrees C during exercise. After exercise, intestinal temperature continued to increase, but no hyperthermia was noted. It has been reported that burned children can safely exercise at room temperature; however, the response in the heat is unknown. This patient did not develop exertional hyperthermia, which we propose is due to his low-fitness level and heat intolerance. However, the potential for hyperthermia would be increased if he was forced to maintain a high relative workload in the heat. We propose that severely burned individuals should be able to safely participate in physical activities. However, the decision to stop exercising should be accepted to avoid development of exertional hyperthermia.

Assessment of muscle function in severely burned children.

INTRODUCTION: The posttraumatic response to a severe burn leads to marked and prolonged skeletal muscle catabolism and weakness, which persist despite standard rehabilitation programs of occupational and physical therapy. We investigated the degree to which the prolonged skeletal muscle catabolism affects the muscle function of children 6 months after severe burn. METHODS: Burned children, with >40% total body surface area burned, were assessed at 6 months after burn in respect to lean body mass and leg muscle strength at 150 degrees /s. Lean body mass was assessed using dual-energy X-ray absorptiometry. Leg muscle strength was assessed using isokinetic dynamometry. Nonburned children were assessed similarly, and served as controls. RESULTS: We found that severely burned children (n=33), relative to nonburned children (n=46) had significantly lower lean body mass. Additionally they had significantly lower peak torque as well total work performance using the extensors of the thigh. CONCLUSIONS: Our results serve as an objective and a practical clinical approach for assessing muscle function and also aid in establishing potential rehabilitation goals, and monitoring progress towards these goals in burned children.