MYOCARDIAL IRRITARILITY— HEGNAUER and COVINO 



343 



8.5 



40 30 



TEMP. °C 



20 10 



COOLING 



10 20 30 40 



REWARMING 



Fig. 3. — Blood pH in dogs, illustrating how the pH shifts to a high level when the respiratory 

 mixture is changed from 5 per cent carbon dioxide in oxygen to oxygen alone at a body tem- 

 perature of 20° C. (By permission of Surgery, Gynecology and Obstetrics.) 



lated and those which had a continuing heartheat were not resuscitated, but of those 

 which went into standstill and were cooled to lielow 10° C, 76 per cent were 

 resuscitated and lived indefinitely. At normal temperatures a similar shift in pH 

 causes a much higher incidence of ventricular fibrillation. Xot only are pH levels 

 important but shifts in pH too, may be crucial. I think that the use of spontaneous 

 respiration during cooling with change to artificial respiration at low temperatures 

 just before doing a thoracotomy, a technic employed by Hegnauer, may produce a 

 detrimental shift in pH. 



These next experiments showed a reduced incidence of ventricular fil)rillation 

 during operations on the heart at 18° C. if 5 per cent carbon dioxide was employed. 

 Right ventriculotomy was done on 9 consecutive dogs without fibrillation. In earlier 

 experiments fibrillation had occurred even with the carbon dioxide ; when the tech- 

 nique was mastered, however, this was avoided. Careful technique is a very im- 

 portant factor in reducing the incidence of ventricular fibrillation. 



In humans the results have been similar ; pH levels above 7.45 have been dan- 

 gerous. To begin with we used an ordinary anesthesia machine and oxygen alone. 

 Among the first 32 patients in which atrial septal defects were repaired under 



