MINISYMPOSIUM

Blood substitutes: where do we stand today?

B . T . K J E L L S T R O MFrom the Experimental Traumatology Unit, Swedish Defence Research Agency and Department of Surgery, Karolinska Institute at Soder Hospital,

Stockholm, Sweden

Background

Sir Christopher Wren was the first to suggest the

concept of using substitutes for blood (e.g. ale or wine)

for transfusion purposes some 400 years ago [1].

Why is there a persisting interest in ‘artificial blood’

when transfusion of homologous blood has been a

safe clinical routine for decades? The threats of

hepatitis and HIV epidemics, with the risk of virus

transmission through ordinary blood transfusions,

incited an intensive research within the field. Before

the development of reliable tests for HIV, the risk of

being infected was estimated to be almost 1 per 2500

transfused patients. Today, that risk has decreased to

about 1 per 800 000 in the developed countries [1] as

a result of improvements in blood bank routines and

blood donor screenings. However, this is unfortu-

nately not the case in many other parts of the world.

Furthermore, in many regions where the need of

blood transfusions may be the greatest, the supply of

donor blood is the smallest. Also in the industrialized

part of the world the situation may become less

satisfactory. The demand of donor blood in USA in

1999 increased by 4.3% whilst the increase in blood

donations was only 2.8% (R.M. Winslow, personal

communication).

There are three major advantages when compar-

ing ‘artificial blood’ products with bank blood [2]:

• Unlike red blood cells (RBC), ‘artificial blood’ can

be sterilized – no spreading of infections.

• Artificial blood does not contain blood group

antigens – no need for typing and cross-matching.

• Artificial blood can be stored for a long time – as a

stable, lyophilized powder.

Today two major categories of ‘artificial blood’

exist, namely modified haemoglobins and perfluor-

ocarbon-based products (Fig. 1). The first generation

of such artificial blood substitutes is currently in

clinical trials [1].

Haemoglobin-based products

Research on ‘artificial blood’, based on haemoglobin

extracted from RBC, started in the 1960s, although

a few papers had already been published before that

period. One early report on the use of haemoglobin–

saline solution in a case of severe postpartum

haemorrhage was published already in 1949 [3].

The unfortunate patient, who finally succumbed as

a result of acute renal failure, had been given all

compatible blood in the hospital blood bank, as well

as large volumes of plasma and crystalloids. After

administration of a total of 2.3 L of haemoglobin–

saline solution, which, in a way, could be regarded

as a very premature version of ‘artificial blood’, an

increase in systolic and diastolic blood pressures

were registered, as well as a simultaneous decrease

in heart rate [3]. It is noteworthy that similar

changes in circulation physiology had been reported

in animals given haemoglobin solutions almost

three decades earlier [4]. Such changes, which

can be attributed to increased vascular resistance

caused by vasoconstriction, were later repeatedly

demonstrated in different species of laboratory

animals and patients given different haemoglobin-

based oxygen carriers [5–7]. The nephrotoxic effects

of free, circulating haemoglobin dimers, which

most likely contributed to the final outcome in the

Journal of Internal Medicine 2003; 253: 495–497

� 2003 Blackwell Publishing Ltd 495

above-mentioned patient, have been known for

decades [1].

Haemoglobin exists in tetrameric form within the

RBC, but outside the RBC each tetramer breaks

down into two dimers. Beside adverse kidney effects,

the dimers also exert a high oncotic pressure and

furthermore release oxygen at low P50 [2]. Conse-

quently, much effort has been invested in modifying

free haemoglobin in order to counteract these

disadvantages. Cross-linking of the haemoglobin

molecules prevents their breakdown into dimers.

Furthermore the haemoglobin molecule has been

encapsulated, and also conjugated (coated) with,

e.g. polyamides, dextran and polyethylene glycol [2].

Research in the area gained momentum around

1985 because of an increasing concern about the

risk of propagating infections (HIV, hepatitis)

through transfusions using donor blood. Another

incentive in the last decades was the upcoming Gulf

War, where it was anticipated, at least in some

scenarios, that a shortage of donor blood would

become a reality. One product from the Baxter

Healthcare by the US Food and Drug Administration

(FDA) [diaspirin cross-linked haemoglobin (DCLHb)]

was tested up to clinical phase III trials. Unfortu-

nately, the trial in patients with traumatic haemor-

rhagic shock had to be prematurely stopped in

1998, when 112 of a planned 850 patients had

entered the study, because the mortality in the

group receiving the test product was more than

twice that of the group receiving standard treatment

(46% vs. 17%) [8]. After this disappointment, the

whole concept of ‘artificial blood’ came into disre-

pute, but during the past few years new, promising

products have been developed and started to be

tested in clinical situations [1].

Perfluorocarbon-based products

Perfluorocarbons are molecules similar to hydrocar-

bons, but the hydrogen atoms have been replaced

with fluorine atoms. These substances are excellent

carriers of oxygen and carbon dioxide. The gases are

dissolved in the perfluorocarbon liquids, and are

easily extracted by the tissues [1]. Perfluorocarbons

are not miscible with water, and must be prepared

as emulsions before they can be administered. At

any given partial pressure of oxygen in equilibrium

with perfluorocarbon, haemoglobin binds more

oxygen than is dissolved in the perfluorocarbon

liquid. Oxygen loading capacity of the latter is

linearly related to the actual partial pressure of

oxygen [1].

A rather spectacular experiment was reported by

Clark and Gollan [9], in which mice were completely

immersed in perfluorocarbon liquids saturated with

oxygen at atmospheric pressure and survived, liquid

breathing, as long as up to 10 min. Thereafter the

animal could be removed from the liquid, breathing

air again, and continue living for several days. The

first trials using perfluorocarbon-based products in

humans were reported in 1978 [10]. A modern

Polymerized Hb Perfluorocarbonemulsion

Conjugated Hb

Crosslinked Hb

Artificial blood substitutes

Fig. 1 Artificial blood substitutes.

4 9 6 B . T . K J E L L S T R O M

� 2003 Blackwell Publishing Ltd Journal of Internal Medicine 253: 495–497

product, based on perfluoroctyl bromide (C8F17Br) is

currently in clinical trials and another product

(a mixture of perfluorodecalin and perfluorotripro-

pyl-amine) together with an emulsifier and phosp-

holipids was approved by the US Food and Drug

Administration (FDA) for clinical use in balloon

angioplasty in 1989 [2].

A great advantage with perfluorocarbon-based

products as ‘artificial blood’ is the fact that they can

be chemically manufactured in large quantities

independently of, e.g. outdated donor blood or other

biological sources.

However, complement activation has been a

major clinical problem with perfluorocarbon-based

products, as has decreasing platelet counts and

increased body temperature. Furthermore, the

patients generally have to breathe 70–100% oxygen

in order for the products to carry enough oxygen

[1, 2].

The future in artificial blood products

In June 2002, the Fourth International Symposium on

Current Issues in Blood Substitute Research (IV CIBSR)

was organized in Stockholm, Sweden. In the present

issue of Journal of Internal Medicine, four papers on

the topic of ‘artificial blood’ are published. The first

of these articles, by Kenneth C. Lowe and Eamonn

Ferguson, sets the stage by letting us know how the

risks inherent in the administration of blood and

blood substitutes are perceived by the public in

general, the educated layperson and representatives

of the medical profession [11]. In the second paper,

Robert M. Winslow gives a thorough overview of the

current status of blood substitute research, including

an exciting definition of the new physiology of the

microcirculation [12]. The third paper by Abdu I.

Alayash and Li-Hong Yeh deals with the molecular

biology and cell signalling mechanisms in relation to

haemoglobin-based oxygen therapeutics [13]. Fi-

nally Thomas M.S. Chang lets us have a preview of

the future generations of red blood cell substitutes

[14].

Conflict of interest statement

Dr T. Kjellstrom is a member of the Scientific

Advisory Board of Sangart Inc.

References

1 Squires JE. Artificial blood. Science 2002; 295: 1002–5.

2 Chang TMS. Blood Substitutes: Principles, Methods, Products

and Clinical Trials, Vol. I. Basel (Switzerland): S. Karger AG,

1997.

3 Amberson W, Jennings J, Rhodes C. Clinical experience with

hemoglobin–saline solutions. J Appl Physiol 1949; 1: 469–89.

4 Bayliss W. Is haemolysed blood toxic? Br J Exp Pathol 1920; 1:

1–8.

5 Hess J, Macdonald V, Brinkley W. Systemic and pulmonary

hypertension after resuscitation with cell-free hemoglobin.

J Appl Physiol 1993; 74: 1769–78.

6 Malcolm D, Hamilton IJ, Schultz S, Cole F, Burhop K. Char-

acterization of the hemodynamic response to intravenous

diaspirin crosslinked hemoglobin solutions in rats. Artif Cells

Blood Substit Immobil Biotechnol 1994; 22: 91–107.

7 Winslow RM. Hemoglobin-Based Red Cell Substitutes. Balti-

more, MD: Johns Hopkins University Press, 1992.

8 Sloan EP, Koenigsberg M, Gens D et al. Diaspirin cross-linked

hemoglobin (DCLHb) in the treatment of severe traumatic

hemorrhagic shock. A randomized controlled efficacy trial.

JAMA 1999; 282: 1857–64.

9 Clark LC, Gollan F. Survival of mammals breathing organic

liquids equilibrated with oxygen at atmospheric pressure.

Science 1966; 152: 1755–6.

10 Naito R, Yokoyama K. An improved perfluorodecalin emul-

sion. In: Jamieson GA, Greenwalt TJ, eds. Blood Substitutes and

Plasma Expanders. New York: Alan R Liss, Inc., 1978: 81.

11 Lowe KC, Ferguson E. Benefit and risk perceptions in trans-

fusion medicine: blood and blood substitutes. J Int Med 2003;

253: 498–507.

12 Winslow RM. Current status of blood substitute research:

toward a new paradigm. J Int Med 2003; 253: 508–17.

13 Yeh L-H, Alayash AI. Redox side reactions of haemoglobin

and cell signalling mechanisms. J Int Med 2003; 253:

518–26.

14 Chang TMS. Future generations of red blood cell substitutes.

J Int Med 2003; 253: 527–35.

Received and accepted 26 February 2003.

Correspondence: B. Thomas Kjellstrom MD, PhD, Experimental

Traumatology, D-Building, 3rd Floor, Soder Hospital, SE-118 83

Stockholm, Sweden (fax: +46-8-616-1364; e-mail: kjellstrom@

foi.se).

M I N I S Y M P O S I U M : C U R R E N T B L O O D S U B S T I T U T E R E S E A R C H 4 9 7

� 2003 Blackwell Publishing Ltd Journal of Internal Medicine 253: 495–497