title: Cold-water immersion and the treatment of hyperthermia: using 38.6°C as a safe rectal temperature cooling limit.
abstract: BACKGROUND
  Cold-water immersion is recommended for the immediate field treatment of exertional heat stroke. However, concerns exist over potential overcooling of hyperthermic individuals during cold-water immersion.
  
  
  OBJECTIVE
  To evaluate the recommendation that removing previously hyperthermic individuals from a cold-water bath at a rectal temperature (T(re)) of 38.6°C would attenuate overcooling.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Participants included 6 men and 4 women (age  =  22 ± 3 years, height  =  172 ± 10 cm, mass  =  67.8 ± 10.7 kg, body fat percentage  =  17.1% ± 4.5%, maximum oxygen consumption  =  59.3 ± 8.7 mL·kg(-1)·min(-1)).
  
  
  METHODS
  After exercising at an ambient temperature of 40.0°C for 38.5 ± 9.4 minutes, until T(re) reached 39.5°C, participants were immersed in a 2.0°C circulated water bath until T(re) decreased to either 37.5°C or 38.6°C. Subsequently, participants were removed from the water bath and recovered for 20 minutes at an ambient temperature of 25°C.
  
  
  METHODS
  Rectal and esophageal temperatures were measured continuously during the immersion and recovery periods.
  
  
  RESULTS
  Because of the experimental design, the overall time of immersion was greater during the 37.5°C trial (16.6 ± 5.7 minutes) than the 38.6°C trial (8.8 ± 2.6 minutes) (t(9)  =  -4.740, P  =  .001). During the recovery period after cold-water immersion, both rectal (F(1,9)  =  50.540, P < .001) and esophageal (F(1,6)  =  20.365, P  =  .007) temperatures remained greater in the 38.6°C trial than in the 37.5°C trial. This was evidenced by low points of 36.47°C ± 0.70°C and 37.19°C ± 0.71°C for rectal temperature (t(9)  =  2.975, P  =  .016) and of 35.67°C ± 1.27°C and 36.72°C ± 0.95°C for esophageal temperature (t(6)  =  3.963, P  =  .007) during the recovery period of the 37.5°C and 38.6°C trials, respectively.
  
  
  CONCLUSIONS
  Immersion for approximately 9 minutes to a rectal temperature cooling limit of 38.6°C negated any risk associated with overcooling hyperthermic individuals when they were immersed in 2°C water.
authors.affiliation: Human and Environmental Physiology Research Unit, University of Ottawa, ON, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gagnon
authors.forename: Bruno B
authors.initials: BB
authors.lastname: Lemire
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Casa
authors.forename: Glen P
authors.initials: GP
authors.lastname: Kenny
mesh_terms: D000328:Adult; D001831:Body Temperature; D003080:Cold Temperature; D017679:Cryotherapy; D005260:Female; D005334:Fever / Q000628:therapy*; D018883:Heat Stroke / Q000628:therapy; D006801:Humans; D007101:Immersion; D008297:Male; D010101:Oxygen Consumption; D005082:Physical Exertion; D012449:Safety