DIFFICULTIES OF EPIDEMIOLOGICAL STUDIES 



Granted, these are purely a matter of observation. And then 

 with surgeons in our position, one of the most important tools 

 is the ability to look at things from the standpoint of their clinical 

 judgments. At the University of Maryland, Division of Neuro- 

 surgery, in the past year almost two hundred patients have been 

 cooled. They are cooling as many patients as we are in cardio- 

 vascular surgery, and appear to be our staunchest competitor; 

 the instance of infections is no greater. This is not good scien- 

 tific evidence, but insofar as taking care of patients is con- 

 cerned, it does appear that cooling for periods up to about two 

 or three hours to levels of approximately 20° C to 30 C does 

 not increase the incidence of infection following surgery. 



MONCRIEF: How about the incidence of infection following 

 profound hypothermia of 10° C? 



BLAIR: The unfortunate fact does remain that the incidence 

 of infection following the use of profound hypothermia which re- 

 quires a mechanical set-up to cool a patient down this low, does 

 result in a higher incidence of infection than if the patient were 

 simply cooled. Whether this is related to the fact that the pa- 

 tients are cooled to the very profound and potentially lethal 

 levels per se, or whether it is due to the fact that it takes a 

 lot of equipment, we really don't know. 



In fact, it does remain that no matter how carefully and how 

 rigidly Lister's ideas are employed today, after an ordinary 

 elective surgical case, if you culture very carefully the sur- 

 geon's hands, the instruments, and the nearby drapes, you will 

 always find bacteria in staggering and distressing amounts. 

 But these patients do not develop postoperative infections. 



The question remains relatively unanswered, and the only 

 thing I might say about this is that the patients are kept at these 

 profound levels for a very, very brief period of time. In many 

 instances, it does hot exceed more than one hour; occasionally 

 two hours. At the University of Maryland -- I guess we were 

 a young, immature group trying to learn — this is the excuse 

 we give for the fact that we had cooled some patients down to 

 levels of 5° C for periods of about two hours. These were children. 



17 



