Aamer Ahmed, FRCA, FESC, FACC
Artificial blood continues to be the holy grail of medicine. Ever since medicine was developed it was always a dream to be able to transfuse a patient with another’s blood. There continues to be extraordinary pressure in modern medicine to find an acceptable and safe alternative to the use of blood as it is essentially a liquid organ transplant. Artificial blood has the potential to transform medicine. Blood performs a multitude of functions and not all of these can be replaced by artificial oxygen carriers.
Modern surgical techniques have developed in tandem with advanced anaesthesia and one of the limiting steps in major surgery is the availability of autologous blood transfusions and blood products. However, as they are human-derived, the supply to blood banks tends to be variable, especially in times of crisis, and there tends to be periods of undersupply. In addition, perceived risks of transmission of infection and risks of transfusion reactions led clinicians to seek an alternative to blood.
The ideal replacement for blood will replace all of its functions:
- Oxygen delivery
- Vascular volume
- Transport of energy and wastes
- Transport of neuro-mediators
Why is there a need for a blood replacement?
- Increasing costs
- Collection, processing, storage
- Concern over infectious agents
- HIV, Hepatitis B and C, CMV, BSE
- Shortage of donors
- Mishaps due to incompatibility
There are four major problems in donor red blood cells and why we seek an alternative to blood.
- The need for cross matching
- Relatively short storage life (42 days)
- Transmission of infectious/anaphylactic agents
- Immunological effects of blood transfusions are associated with higher frequencies of surgical infections, delayed wound healing, and progression of malignant disease.
The ideal blood substitute is non antigenic, similar to natural haemoglobin in terms of oxygen transport and CO2removal; does not cause increases in arterial or pulmonary blood pressures; has a sufficient half-life in the circulation; does not form methaemoglobin, activate complement, increase white cell count, react with plasma substitutes or platelets; is stable at room temperature; not nephrotoxic; is easy to administer; easily stored long term; is easily available; and does not cause oxidation or free radical formation.
This is quite a wish list and at the current time we are not as close to this ideal as we would like to be. There are different types of artificial oxygen carriers:
- Haemoglobin-based oxygen carrying solutions
- Perfluorocarbons in the form of emulsions
There is an ongoing debate about the pros and cons of each class of solution. Neither is perfect, each has limitations.
Artificial blood solutions would have potential use in many fields of medicine. In elective surgery they could be used for isovolumic haemodilution and perioperative volume replacement, in cardiovascular surgery and trauma patients as pump prime and volume replacement. They could have a role in the perfusion of ischemic tissues in stroke, peripheral vascular disease, and haemolytic anaemias. Potentially they could be considered for use in haemoglobinopathies. Organ preservation for transplant and cardioplegic solutions would be a use pre-transplant.
There are limitations to where we are with the current state of the art. These will be discussed in the ESA Focus Meeting in Sofia, Bulgaria, in November 2018 to which I warmly invite you all as it covers a theme of perioperative transfusion, haemostasis, and fluid balance, all of which are essential areas of clinical practice for anaesthesiologists. This was also an important theme that was covered in the recent ESA Severe Perioperative Bleeding Management Guidelines Update chaired by Prof Sibylle Kietaibl and the taskforce under her leadership, which was published in the European Journal of Anaesthesiology(EJA) in 2016. Equally, the theme of VTE prophylaxis was covered by another expert taskforce chaired by Prof Charles Marc Samama that led to the publication of these guidelines in 2017 in the EJA.
The meeting will be a great place to learn from the experts about patient blood management, which is a newer concept allowing us to think about the entire patient journey from primary care, where the treatment of anaemias can begin using iron therapy, through to the perioperative period, where advanced techniques of coagulation management and cell salvage can be used, as well as how to optimise postoperative blood loss. We will also have details about point of care testing such as TEG and ROTEM and how their use is clinically indicated. So, do come and join what promises to be a well-attended meeting and contribute to an exciting scientific programme.
I look forward to seeing you in Sofia.
Dr Aamer B Ahmed
ESA Member Transfusion and Haemostasis Committee
Chairperson ESA Communications Committee
Member of ESA Taskforce for VTE Prevention Guidelines
Member of ESA Taskforce for Severe Perioperative Bleeding