Comparison of Rehydration Regimens for Rehabilitation of Firefighters Performing Heavy Exercise in Thermal Protective Clothing: A Report from the Fireground Rehab Evaluation (FIRE) Trial

Abstract

Background. Performing fire suppression activities results in cardiovascular stress, hyperthermia, and hypohydration. Fireground rehabilitation (rehab) is recommended to blunt the deleterious effects of these conditions. Objective. We tested the hypothesis that three rehydration fluids provided after exercise while wearing thermal protective clothing (TPC) would produce different heart rate or core temperature responses during a second bout of exercise in TPC. Methods. On three occasions, 18 euhydrated firefighters (16 men, two women) wearing TPC completed a standardized, 50-minute bout of upper and lower body exercise in a hot room that mimicked the National Fire Protection Association (NFPA) rehabilitation guidelines of “two cylinders before rehab” (20 minutes of work, 10 minutes of recovery, 20 minutes of work). After an initial bout of exercise (bout 1), subjects were randomly assigned water, sport drink, or an intravenous (IV) infusion of normal saline equal to the amount of body mass lost during exercise. After rehydration, the subject performed a second bout of exercise (bout 2). Heart rates, core and skin temperatures, and exercise durations were compared with a two-way analysis of variance (ANOVA). Results. Subjects were firefighters with a mean (± standard deviation [SD]) age of 28.2 ± 11.3 years and a mean peak oxygen consumption (VO_2peak) of 37.4 ± 3.4 mL/kg/min. The mean amount of fluid provided during the rehabilitation period was 527 ± 302 mL. No subject could complete either the pre- or postrehydration 50-minute bout of exercise. The mean (±SD) times to exhaustion were longer (p < 0.001) in bout 1 (25.9 ± 12.9 min, water; 28.0 ± 14.1 min, sport drink; 27.4 ± 13.8 min, IV) compared with bout 2 (15.6 ± 9.6 min, water; 14.7 ± 8.6 min, sport drink; 15.7 ± 8.0 min, IV) for all groups but did not differ by intervention. All subjects approached their age-predicted maximum heart rate at the end of bout 1 (180 ± 11 bpm) and bout 2 (176 ± 13 bpm). Core temperature rose 1.1°C ± 0.7°C during bout 1 and 0.5°C ± 0.4°C during bout 2. Core temperatures, heart rates, and exercise times during bout 2 did not differ between the rehydration fluids. Conclusions. Performances during a second bout of exercise in TPC did not differ when firefighters were rehydrated with water, sport drink, or IV normal saline when full rehydration was provided. Of concern was the inability of all subjects to complete two consecutive periods of heavy exercise in TPC, suggesting that the NFPA's “two cylinders before rehab” guideline may not be appropriate in continuous heavy work scenarios.

Key words: :

• cardiovascular strain
• thermal stress
• performance
• hydration