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 m 2). 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 ± 0.01 "°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.