REVIEW AND APPRAISAL OF PART V 



R. D. DRIPPS 



Three methods of inducing hypothermia in man have received the most atten- 

 tion, i.e., (a) use of drugs alone, (b) appHcation of cold to various body surfaces, 

 and (c) cooling of blood removed from and subsequently returned to the body. 

 Unfortunately, few comparative studies of these techniques have been reported in 

 humans so that much remains to be learned about the optimum approach to reduc- 

 tion of body temperature in clinical practice. In this brief review established data 

 will be presented, together with suggestions for future investigation. 



It is evident that no single drug or group of drugs has produced a significant 

 lowering of body temperature without added cold. Neither chlorpromazine, 

 Phenergan, Hydergine, or meperidine, alone or in combination, have caused signifi- 

 cant hypothermia. A few degrees reduction in body temperature over a two to 

 four hour period is the most that can be expected in the average adult patient. 

 Some or all of these substances are of value as adjuncts to cooling, but none can 

 stand as a primary agent. 



Direct cooling of blood appears to produce a more rapid reduction of body tem- 

 perature in adults than does any method of surface cooling. Direct blood cooling 

 is also alleged to be associated with less compensatory shivering and vasoconstric- 

 tion. Damage to skin, subcutaneous tissue and peripheral nerves are infrequent with 

 this method in comparison with surface cooling. 



Unsolved problems include some of the following : 



Ideal rate of cooling. From the practical standpoint the more rapidly one can 

 lower body temperature, the less time is wasted. In infants and children tempera- 

 ture reduction can be achieved with extraordinary rapidity by surface cooling. This 

 is not true in adults where greater surface area and increased subcutaneous fat slow 

 up temperature change. The hazards of rapid cooling deserve further studv. Ir- 

 regularities in cardiac rhythm have been alleged to follow rapid hypothermia. The 

 concomitant effect of such factors as inadequate ventilation, hypotension, and 

 shivering has not been assessed, so that controlled experiments are needed before 

 one can determine the safest rate of reduction of body temperature. 



If a relatively rapid rate of cooling is found safe, can the lowering of tempera- 

 ture following surface cooling be increased by tilting the subject, changing his 

 position regularly, or by brushing or rubbing the skin vigorously ? Clinical impres- 

 sions suggest that these adjuncts deserve appraisal. 



Post-cooling downward drift of body temperature. Once active cooling has 

 been stopped, a continued decline of body temperature has been reported by a 

 number of workers. Again this appears more frequently in infants and children. 

 The predictability of the extent of this drift is not reliable. The causes and pre- 

 vention of this continued fall in temperature require investigation. 



Anesthetic management. There is little agreement as to the pre-hypothermia 

 sedation, the anesthetic agents and techniques, or the muscle relaxants which are 

 preferable as cooling is induced. Substances which are destroyed in the bodv will 



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