[Effects of shivering on airway rewarming]

To investigate the effects of shivering on airway rewarming.

The hypothermic dog model without shivering was established by immersing an anesthetized dog in cold water and administering atracurium to inhibit the dog shivering. The model dog respired warm fully humidified (40-45 degrees C, RH 99.9%) air and room temperature air(19 +/- 1 degrees C, RH 30% - 75%) to rewarm each for 2 hours, the priority of different temperature air respired was arranged randomly. After rewarming for 4 hours, the relaxed dog breathed warm humidified air by positive pressure ventilation in order to restore its spontaneous respiratory. Then the dog continued to respire warm humidified air spontaneously until the esophageal (Te) and rectal temperature (Tr) of the dog achieved the same degrees as the dog was immersed in the water. The metabolic heat production was detected by indirect calorimetry during the experiment.

(1) When the shivering was inhibited, inhaling warm humidified air for 2 hours made the Tr and Te of the dogs increase 0.26-0.39 degrees C and 0.44-1.11 degrees C per hour respectively, inhaling air at room temperature for 2 hours made Tr and Te of the dogs decrease 0.24-0.51 degrees C and 0.58-0.67 degrees C per hour, respectively. And the changes in Tr and Te of the dogs were unrelated to the priority of inhaling air at different temperature. (2) When the dog with shivering respired spontaneously warm humidified air, the rewarming rates of Tr and Te were 2.26-2.33 degrees C/h and 1.96-2.38 degrees C/h respectively, quicker than those of the dogs whose shivering was inhibited. (3) Compared with metabolic heat production of the unshivering dog respiring warm humidified air by positive pressure ventilation, that of the shivering dog respiring warm humidified air spontaneously increased outstandingly, shivering thermogenesis made the rewarming rates increased obviously.

Airway rewarming is a method conducive to rewarming of hypothermia. When the body is shivering, the metabolic heat production increases obviously, that makes the rewarming rate increase markedly. So the shivering must be inhibited in order to eliminate the interference of shivering thermogenesis when the effects of airway rewarming are detected.