Immersion of distal arms and legs in warm water (AVA rewarming) effectively rewarms mildly hypothermic humans.

INTRODUCTION: Active rewarming of hypothermic victims for field use, and where transport to medical facilities is impossible, might be the only way to restore deep body temperature. In active rewarming in warm water, there has been a controversy concerning whether arms and legs should be immersed in the water or left out. Further, it has been suggested in the Royal Danish Navy treatment regime, that immersion of hands, forearms, feet, and lower legs alone might accomplish rapid rates of rewarming (AVA rewarming). METHODS: On three occasions, six subjects (one female) were cooled in 8 degrees C water, to an esophageal temperature of 34.3+/-0.8 (+/-SD) degrees C. After cooling the subjects were warmed by shivering heat production alone, or by immersing the distal extremities (hands, forearms, feet and lower legs) in either 42 degrees C or 45 degrees C water. RESULTS: The post cooling afterdrop in esophageal temperature was decreased by both 42 degrees C and 45 degrees C water immersion (0.4+/-0.2 degrees C) compared with the shivering alone procedure (0.6+/-0.4 degrees C; p < 0.05). The subsequent rate of rewarming was significantly greater with 45 degrees C water immersion (9.9+/-3.2 degrees C x h(-1)) than both 42 degrees C water immersion (6.1+/-1.2 degrees C x h(-1)) and shivering alone (3.4+/-1.5 degrees C x h(-1); p < 0.05). CONCLUSION: The extremity rewarming procedure was experienced by the subjects as the most comfortable as the rapid rise in deep body temperature shortened the period of shivering. During the extremity rewarming procedures the rectal temperature lagged considerably behind the esophageal and aural canal (via indwelling thermocouple) temperatures. Thus large gradients may still exist between body compartments even though the heart is warmed.

"Paradoxical undressing" in fatal hypothermia.

The phenomenon called paradoxical undressing has been described from 33 cases of hypothermia collected from Swedish police reports. The cases were almost evenly distributed with regard to sex, age, and geographical distribution. The cases occurred more frequently in open land although cases from town areas were also found. Most incidents were recorded from November to February at low ambient temperatures, although cases were also reported at temperatures above 0 degree C. Arteriosclerosis and chronic alcoholism were important concomitant illnesses, the latter being frequent in middle-aged men. Epilepsy, diabetes, and pregnancy were present in single cases. Ethanol and other drugs were present in 67% of the males and in 78% of the females, ethanol predominating in men and various psychotropic agents in women. The mean blood ethanol concentration in males was 0.16% and in females, 0.18%. Most frequent findings at necropsy were purple spots or discoloration on the extremities, pulmonary edema, and gastric hemorrhages. It is concluded that paradoxical undressing might be explained by changes in peripheral vasoconstriction in the deeply hypothermic person. It represents the last effort of the victim and is followed almost immediately by unconsciousness and death.

Thermal problems in plethysmography and pressure/volume recording.

Where volume changes are recorded as the concomitant changes in pressure, modern, fast-responding pressure transducers might record not only the pressure changes due to volume changes in the measured object but also the heat of compression, showing itself as an overshoot or hysteresis phenomenon in the calibration curves. Introduction of an effective heat sink (e.g. copper mesh) within the air space in the plethysmograph might absorb this heat and thereby diminish the overshoot phenomena. The effect is not of practical importance in classical venous occlusion plethysmography where rapid changes only contribute to a smaller part of the total volume change during venous occlusion. When rapid changes, as in volume pulse recordings, are to be evaluated, the effect must be taken into consideration and should be reduced.

Physiological reactions to wet-cold.

Changes in extremity temperatures during general cold stress were investigated. The changes in local temperatures were found equal to those seen under circulatory arrest. In order to investigate the influence of these changes on motor function, the relation between local temperature and nervous conduction velocity in a peripheral motor nerve (n. ulnaris) was carried out in subjects exposed to a minor cold stress (to aboid the influence of Lewis hunting reaction). The decrease in conduction velocity was found to be 15 m/s per 10 degrees C fall in temperature. At a local temperature of 8-10 degrees C a complete nervous block was established. This leads to an explanation of the clinical findings in wet-cold situations, where the very rapid onset of physical impairment corresponds to the effect of a local cooling in the extremities and not, as commonly accepted, to a developing general hypothermia.