HYPOTHERMIA AND CARDIAC SURGERY— SWAN 403 



ai-f in the hii;li twenties (C). We do not consider this a serious development, and 

 most will re\ert to sinus rhythm at ahout the same temperature when rewarming. 



Ahout five minutes hefore the moment of circulatory occlusion, further curare is 

 given to prevent contraction of the diaphragm. A determination of blood pH is 

 made at this time. We believe it desn-al)le that the patient be in a state of respiratory 

 alkalosis, with a pH of 7.5 or greater. During occlusion the lungs are allowed to 

 collapse completely, and respiration is discontinued. The surgeon occludes the inflow 

 of blood to the heart; then, after a few seconds, occludes the aorta about one inch 

 distal to the valve and injects 0.8-1.5 cc. neostigmine 1 : 4000 into the base of the 

 aorta so that it will perfuse the coronary system. After an additional 10 or 15 sec- 

 onds, the operative manipulation is performed. 



Upon release of circulatory occlusion, the lungs are again ventilated with oxygen, 

 and hyperventilation resumed. The patient may receive only oxygen until the end 

 of the procedure. If further anesthetic agent is needed it usually consists of 50-50 

 nitrous oxide-oxygen. 



Diathermy is now begun, applied intermittently— one minute o&, two on— to 

 help prevent skin burns. Attempt is made to have the patient have an auscultal)le 

 blood pressure of 90 systolic or above before the thoracotomy is finally closed, in 

 order to avoid later bleeding when the hypotension of hypothermia rises to normal 

 levels. Upon completion of closure, the patient may or may not be further warmed 

 in the tub filled with water at 45° C, depending on temperature. The endotracheal 

 tube is removed when spontaneous respirations appear adequate. The usual tem- 

 perature of waking is about 34° C. 



The immediate postoperative period is extremely critical. Evaluation of elYective 

 circulating blood volume and myocardial function is extraordinarily difficult. A 

 few cases of severe shock occurred at this time. Blood volume studies are done at 

 this time to compare with preoperative levels. Improved understanding of the state 

 of the circulation immediately following cooling is badly needed in order to control 

 this stage of hypothermia more intelligently. - 



In the management of hypothermia, we have emphasized the following safety 

 measures on the basis of personal experimental and clinical experience. We believe 

 that a sudden shift of blood pH from respiratory acidosis toward normal may incite 

 onset of ventricular fibrillation and that a high pCOo sets the stage for the induction 

 of cardiac arrest. For this reason, we deliberately strive for a respiratory alkalosis 

 throughout the procedure. 



We use neostigmine for the coronary perfusion on the basis of experimental data 

 suggesting its value. Concomitant with its clinical use, the incidence of ventricular 

 fibrillation fell markedly. In fact, we have had no patient undergo this complication 

 in the last thirty cases. 



The prevention of coronary air embolus is highly important. To this end, we 

 make it a practice to occlude the ostia of the coronary arteries with a non-crushing 

 clamp during the open portion of the procedure, and to evacuate air by flooding the 

 heart with Ringer's solution before circulation is resumed. Clamping the coronary 

 arteries removes all coronary blood flow throughout the occlusion period and, there- 

 fore, is prol)ably undesirable from this point of view. The maneuver probably 

 shortens the safe duration of occlusion. However, the risk of coronary emlwlism 



