366 
SURGERY AND TRANSPLANTATION 
of the organ was short and the proper storage 
temperature was used.^ The advantage of sim- 
ple hypothermia for the storage of organs is 
simplicity, low cost, and ease of transportation 
of the graft. However, the degree of injury sus- 
tained by the graft during simple hypothermic 
storage, although difficult to assay with preci- 
sion, is not insignificant. With human cadaver 
transplants, approximately 50% of recipients 
required postoperative dialysis after receiving 
kidneys preserved by this method. 
As contrasted to simple hypothermia, the 
other practical, widely used method which al- 
lows rapid recovery of function after short- 
term preservation of kidneys is hypothermic 
perfusion. In addition to permitting longer pe- 
riods of preservation, perfusion helps to dis- 
tinguish between functioning and non-function- 
ing grafts prior to implantation. ^i'' However, 
it must be noted that the currently employed 
perfusion techniques do not allow for an in- 
definite maintenance of organs in vitro. The 
failure of organs to survive artificial perfusion 
beyond a certain point of endurance has been 
attributed to severe changes in the vasculature 
and the microvasculature of the perfused organ. 
Prolonged maintenance of perfused organs in 
vitro is also associated with a risk of bacterial 
contamination which increases greatly with 
each additional day of storage. 
It is clear that extracorporeal organ mainte- 
nance could be of increased value in clinical 
transplantation if the extracorporeal life span 
of the graft could be extended to weeks and 
months rather than hours. In the present state 
of technology this goal cannot be reached by 
perfusion. In fact, the only means by which in- 
definite organ storage can be anticipated is by 
freezing. Therefore, much experimental work 
on organ freezing has been performed. The 
retention of tissue and cell viability following 
freezing and thawing is not possible without the 
addition of cryoprotective agents. In the case of 
whole organs, these can be delivered only by 
perfusion. 
Most tissues, when subjected to freezing in 
the presence of cryoprotective agents, survive 
on thawing, provided only small pieces are be- 
ing frozen. The same holds true with small com- 
plex organs such as parathyroid glands, rat 
adrenals, chicken embryonic hearts, and in- 
testinal segments.^2-14 Exactly opposite results 
are obtained with freezing of more complex, 
larger organs, even with the use of the same 
cryoprotective agents and freezing rates. ^^'^^ 
TOLERANCE TO ISCHEMIA 
The tolerance to ischemia varies greatly with 
individual organs, as it does with species of 
animals. Most parenchymatous organs, if trans- 
planted after 1-2 hours of normothermic ische- 
mia, will not function adequately. The adult 
human brain is uniquely susceptible to ischemic 
damage and is said to be irreversibly damaged 
by 10-15 minutes of ischemia. In the case of 
some organs, simple cooling will permit sur- 
vival of isolated organs up to 8-24 hours. 
The task of defining organ viability and var- 
ious methods for assaying viability do not fall 
within the scope of this paper. For this purpose 
the reader may be referred to special publica- 
tions devoted to the subject.^'^"^" It may suffice 
to state that, for the purposes of the present 
discussion, the only meaningful assay of the 
viability of preserved organs is the resumption 
of function of such organs on implantation. 
The function of organs rendered ischemic by 
the interruption of blood flow is obviously sus- 
pended until circulation is restored. The func- 
tion of transplanted organs is usually impaired 
following completion of the vascular anasto- 
moses and restoration of the blood flow. If the 
ischemic injury is not too severe this functional 
impairment is only transient. If, on the other 
hand, ischemic injury is severe enough to pro- 
duce an irreversible change in an organ even 
before it is subjected to preservation proce- 
dures, the organ will not function on implanta- 
tion. 
The dog kidney seems to be uniquely resistant 
to ischemia, as compared to other organs and 
other animal species. Uncooled kidneys trans- 
planted as long as one hour following ligation 
of the renal artery usually support the life of an 
experimental animal in the presence of the con- 
tralateral nephrectomy. The experience of the 
present writer indicates that rabbit kidney will 
not resume function after 20-30 minutes of 
ischemia. The kidneys of baboons and rhesus 
