404 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



is so great that, in our hands, it is one of the serious hmiting factors relating to 

 open-heart techniques. In order to fill the heart with the Ringer's solution, the 

 incision in the heart must be positioned at the uppermost portion of the heart. This 

 requires wide exposure and demands a Ijilateral thoracotomy with a sternum-splitting 

 incision. It also limits the cardiotomy in our hands to a right-sided incision; we 

 have not been able to devise a safe left-heart approach which places the incision 

 uppermost. This technique has been effective in our hands to the extent that 

 coronary air embolus has occurred only twice in this series. Both patients were 

 resuscitated by pumping and massaging the air through to the venous side of the 

 coronary circulation. 



Cardiac resuscitation has been done in standard fashion using intermittent manual 

 compression, electric shock, potassium chloride, calcium chloride, and adrenalin as 

 appeared indicated. The diathermy is an important adjunct in warming the patient 

 when attempting to revert ventricular fibrillation. 



No preoperative drugs have been used to affect cardiac action, except that digitalis 

 was given to patients in frank failure. Pre- and postoperative penicillin is routinely 

 used. 



INDICATIONS 



In congenital or acquired heart disease for which standard closed operative tech- 

 niques are planned, the indications for hypothermia have been the following. In 

 cyanotic heart disease, it was thought that the reduction in oxygen demand would 

 result in better oxygenation of the tissues. A blue child gradually becomes pinker 

 as temperature falls. We consider operative risk to be improved under these condi- 

 tions. In heart disease associated with severe tachycardia, the extremely rapid rate 

 we consider per se as undesirable. A patient with so-called atypical patent ductus, 

 with a large heart pounding at 1 70, changes to one whose heart is quietly beating 

 at 90. We are not sure, because we have not had sufficient experience, whether heart 

 failure may not also be an additional indication. 



On the other hand, patients with valvular disease resulting in left ventricular 

 hypertrophy and strain appear to tolerate hypothermia less well. Our experience 

 with this group is very small as yet, and we have only very preliminary impressions. 

 It may develop that for some cardiac patients hypothermia improves risk ; for others 

 it does not. 



The main indication for hypothermia in this series, however, has been its use to 

 allow total circulatory arrest in order to perform direct-vision intra-cardiac opera- 

 tions. Selection of patients w^as largely limited to congenital diseases for which 

 pre-existing operative techniques had proven to yield poor or inconsistent results, 

 for example, isolated pulmonary valvular stenosis, or those for which standardized 

 methods had not yet been developed, for example, septal defects. 



COMPLICATIONS 



Postoperative evaluation of the state of the circulation for several hours post- 

 hypothermia is extremely difficult. During this period, w^e lost four patients due to 

 hemorrhage, which was unrecognized and therefore untreated. For this reason, 

 warming with diathermy until blood pressure is ol)tainable before closing the chest 



