Section Review: Cardiovascular & Renal: Blood substitutes in development

Abstract

‘Blood substitutes’ are products designed to be used when blood is either unavailable or in short supply. Three major classes of products are being developed and tested, including haemoglobin-based oxygen carriers, perfluorocarbon-based oxygen carriers, and liposome-encapsulated haemoglobin. Other novel products are in very early stages of development. None of the products perform all the functions of blood; neither do they persist in the circulation as long as human red blood cells. However, they all carry and transport oxygen to tissues and can support life temporarily until patients can either regenerate their own red cells or can be transfused with banked blood. In the past, the main obstacle to the development of blood substitutes has been in understanding their side-effects. Having overcome the most significant toxicities of each class of products, rather minor problems persist, but these will probably not prevent clinical acceptance and regulatory approval. An important consequence of the extensive research that has been done on blood substitutes in the last decade has been an appreciation that when oxygen carriers are not restricted to the red blood cell, the way in which oxygen is delivered to tissues is markedly different. This should not be unexpected, since all mammalian circulatory systems are geared to cellular oxygen delivery. Thus, in addition to furnishing an exciting new class of therapeutics, work in this field is providing new insight into fundamental principles of physiology. This review provides a brief overview of the different types of blood substitutes in development and attempts to assess the current state of progress of each product.

Key Words:

• blood substitutes
• haemodilution
• haemoglobin
• liposomes
• microcirculation
• oxygen transport
• perfluorocarbons
• transfusions
• trauma