The Development of a Plasma Volume Expander 57 



in the same manner as does the plasma protein. Although opinion 

 may vary as to the optimal length of stay of the substitute in the 

 blood stream, it is generally agreed that a half-life of 12-20 hours 

 is satisfactory; i.e., 50^ of the injected plasma substitute solution is 

 to remain after 12-20 hours. A corollary requirement is that the 

 material must not remain in the blood stream indefinitely or be stored 

 in the tissues indefinitely, as it is then liable to give rise to undesirable 

 reactions. Having served its purpose for the time stipulated, it should 

 be excreted or metabolized, preferably the latter if in the process of 

 metabolism it can serve as a source of nutritive energy or as suitable 

 building material for protein lost in the original trauma. The material 

 must not be toxic or produce any undesirable physiologic response 

 such as hypotensive action. It must be non-pyrogenic and non- 

 antigenic. It must not interfere with the clotting and other hemostatic 

 properties of the blood, and it must not be harmful to any of the 

 formed elements of the blood. It should not materially increase the 

 viscosity of the blood. 



In addition to these physiological criteria certain physical and 

 chemical requirements are imposed by considerations of practicality. 

 The material must be readily and cheaply available in large quantities. 

 It must be easy to sterilize, stable to conditions of long storage and 

 climatic extremes of heat and cold, must not gel at low temperatures, 

 and if possible should be transportable in minimal bulk volume. 



During the course of two world wars many substances have been 

 proposed and tried, which have met the above criteria with varying 

 degrees of satisfaction. 



Though the subject is too familiar and elementary to warrant any 

 detailed presentation of these materials, a brief review may serve to 

 provide background for further advances in this field. 



Chemically most of the materials proposed and used fall into two 

 general classes: they are either polysaccharides or proteins. Of the 

 latter class human serum albumin or human plasma itself should 

 obviously provide the best substitute therapy for loss of plasma. This, 

 indeed, they do, but there are certain drawbacks connected with their 

 large-scale massive use. The first of these is connected with the 

 amount that might be required in military or mass disaster. It is 

 estimated that an average of some 30-40 units (500 cc. per unit) would 

 be required to treat the average case of severe burn. Requirements 

 for other types of fluid loss or shock vary with the nature of the 

 condition but are generally less than this amount. It is evident then 

 that an enormous amount of human blood would be required to stock- 



