Effectiveness of Heat Donation Through the Head or Torso on Mild Hypothermic Rewarming
Condition: Rewarming by Shivering Heat Production Only; Rewarming by External Heat to the Torso; Rewarming by External Heat to the Head
MeSH terms: Hypothermia
Study type: Interventional

Summary: 
      The study will compare the rewarming effectiveness of heat donation through the head or the
      torso during rewarming of mildly hypothermic subjects. Warming will be accomplished through
      either forced-air warming or using a charcoal heater; both units are commonly used for
      warming. The investigators hypothesize that head warming will be as, or more, effective
      compared to
    

Detailed description: 
      Dr. Gordon Giesbrecht is studying/comparing the effectiveness of heat donation through the
      head or the torso in rewarming a mildly hypothermic individual. A rigid forced-air warming
      cover for the head or the torso will be used to rewarm the hypothermic individuals.

      Subjects will be asked to participate in three experimental trials, separated by at least 48
      hours. Each trial will last about 4 hours (1 hour for setup, 1 hour for cooling, and 2 hours
      for rewarming and removal of instrumentation).

      On each of the three trials, subjects will undergo immersion to the level of the sternal
      notch in a tank of 8˚C water for up to 60 minutes. They will then exit the water, be dried
      off and lie in a hooded sleeping bag with the head inside the hood where one of the three
      warming procedures will be administered for 60 minutes or until core temperature returns to
      normal values ( ̴ 36.5-37˚C).

      A. Spontaneous rewarming (Shivering Only) - In this control condition, no external heat will
      be provided and you will rewarm spontaneously with the heat produced from shivering.

      B. Head Warming (Head): Either of these rewarming methods will be used:

        -  Forced-Air Warming to the Head (FAW-H) - A modified rigid forced-air warming cover will
           be placed over your head. Warm air ( ̴43˚C) will blow into the cover through an inlet on
           top of the cover and will escape from the bottom of the cover. You will be breathing
           warm air (̴ 43˚C).

        -  Charcoal Heater to the Head (CH-H) - A charcoal heater will be placed on right side of
           your face/head with ducts wrapping around the dorsum of the head, anteriorly over the
           forehead, nose, chin and the neck, not covering the eyes or the mouth. You will be
           breathing ambient air (̴ 22˚C).

      C. Torso Warming - Either of these rewarming methods will be used:

        -  Forced-Air Warming to the Torso (FAW-T) - A specially designed portable rigid forced-air
           cover (PORIFAC) will be placed over your torso and the upper thighs. Warm air (̴ 43˚C)
           will blow into the cover through an inlet above the abdomen and will escape from the
           bottom of the cover. Participant will be breathing ambient air (̴ 22˚C).

        -  Charcoal Heater to the Torso (CH-T) - The charcoal heater will be placed on your
           anterior chest with a towel in between. The flexible ducts will be applied to the areas
           of high heat transfer i.e. over the shoulders, neck, and then anteriorly under the
           axillae to cross over the lower anterior chest. You will be breathing ambient air at
           room temperature (~22˚C).

      After 60 minutes of warming, subjects will be placed in a warm water bath (40-42˚C) until
      they are comfortable and core temperature returns to normal values (̴ 36.5-37˚C).

      Outcome measures include rate of core cooling, afterdrop amount, rate of rewarming, skin heat
      flux, oxygen consumption and shivering intensity.
    

Intervention name(s): Rewarming modality
Intervention type(s): Device
Intervention description(s): A commercial charcoal heater will be applied to the torso or the head in two of the trials. The control trial involves shivering only.
Other intervention name(s): Charcoal heater; STK Heatpac
Intervention MeSH terms: Charcoal
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: rewarming; core cooling; afterdrop; pre-hospital treatment; hypothermia