PROBLEMS IN METHODS OF INDUCING HYPOTHERMIA BY 

 USE OF DRUGS AND INTERNAL COOLING 



J. FRANCIS DAMMANN and WILLIAM H. MULLER, JR. 



External cooling by means of ice or cold water immersion has been the method 

 selected by the majority of surgical teams^"-^ in this hemisphere. Several of the 

 European groups--""' have believed, however, that problems and hazards involved 

 in hypothermia have been decreased by the use of a direct blood cooling unit. Thus, 

 investigation in this country has split along two lines: (1) The investigation of an 

 extracorporeal pump-oxygenator system, and (2) the investigation of hypothermia 

 by means of external cooling. The Europeans have combined these techniques and 

 have, at least in part, demonstrated that the combination simplifies both hypothermia 

 and the extracorporeal circulation. 



Direct cooling of blood in an extracorporeal circuit was first introduced abroad 

 by Boerema-- in 1951 and Delorme-^ in 1952. Their work was extended by Ross 

 and Brock-^' ^®' ^'' and blood stream cooling is now being used by Brock during 

 intracardiac surgery on humans. In this country Gollan-^"^^ has been the chief ex- 

 ponent of direct blood stream cooling. His work has been in the experimental ani- 

 mal, and experience in human patients has been very limited. 



There are three different methods of direct blood stream cooling. Following 

 Delorme's work, Ross and Brock'--'' have developed a technique of vein-to-vein 

 cooling. Blood is sucked through a catheter from the superior vena cava and, after 

 being pumped through a siliconized polyethylene cooling coil, is returned to the 

 inferior vena cava. If the thoracic cage is not opened, catheters are inserted into the 

 superior and inferior vena cavae through the external jugular and femoral veins. 

 During thoracotomy it was found that the most efficient method was the insertion 

 of both catheters into the right auricular appendage ; one catheter being directed 

 up the superior vena cava and the other down the inferior vena cava. When starting 

 a cardiac operation, Brock is prepared to use hypothermia but the final decision is 

 not made until the chest is opened and the cardiac malformation is analyzed. If 

 cooling is elected, the catheters can be inserted rapidly and the blood cooled at a 

 rate of one degree centigrade per five minutes. Brock feels that there are several 

 advantages to this method of cooling : It is rapid, readily reversible, can be applied 

 easily in the open chest, and does not involve cannulation of any major arteries. 



The second method consists of withdrawing Ijlood from one of the large systemic 

 veins and, after passing the blood through a cooling coil, returning the blood to 

 the patient through an intra-arterial catheter. This technique was advocated by Ross 

 and Brock as a means of increasing coronary blood flow and thereby improving 

 cardiac function. In the experimental animal a striking improvement in heart action 

 and a reduced incidence of ventricular fibrillation during ventricular cardiotomy 

 was noted when a simple venous-arterial cooling circuit was added. Later, they 

 modified this simple circuit by the addition of a reservoir of oxygenated blood so 

 that the oxygen content of the perfusing venous blood was increased. Lewis and 

 co-workers^^' -° also have perfused the coronaries with venous blood at low tempera- 



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