While there’s no denying blood transfusions save lives, there’s a growing awareness of the potential risks of these ‘liquid organ transplants’.
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Countless lives have been saved in the hundreds of years that people have been receiving blood transfusions.
Transfusions replenish blood lost through trauma, illness or surgery. They are a medical safety net; there for when surgery doesn’t quite go according to plan, and patients need a little top-up. They are also a lifeline for people with inherited blood disorders, certain rare diseases or who are undergoing chemotherapy.
But the field of transfusion medicine is changing. Instead of being viewed as an inert recharging of fluid, we are now coming to appreciate that a blood transfusion is essentially a liquid organ transplant, says National Blood Authority chair Leigh McJames; and like any other organ transplant, it has its risks.
The stuff of life
Australia has one of the safest blood supplies in the world, but that doesn’t mean blood transfusion is 100 per cent safe.
McJames says blood occupies a strange and somewhat privileged position in modern medicine, and that it has evolved as a treatment option without the same level of research scrutiny at least on the patient outcomes side of things that other treatments are subjected to.
“Nowadays if you have a modern pharmaceutical it goes through the whole bunch of clinical trials before it’s registered, but blood didn’t come to health that way,” he says.
But as far back as 1990, studies were hinting that blood transfusions carried more risks than had long been thought, says haematologist Professor James Isbister.
“It was becoming apparent that the mere fact you received a blood transfusion was a risk factor or was associated with poorer outcomes… in terms of increased length of stay in hospital, certain post-operative infections that weren’t directly from the transfusion, more likely to be ventilated, more likely to be intensive care,” says Isbister, Clinical Professor of Medicine at the University of Sydney Medical School.
Another clue that transfusions carried risks came from ‘restrictive transfusion’ studies done in otherwise stable patients, where the doctor was either instructed to give a transfusion only if a patient’s haemoglobin (the red protein in blood cells that carries oxygen) levels dropped to a certain point, or to treat as they normally would do.
“These trials have essentially all shown that a restrictive policy did not leave the patients any worse off and there is some evidence that they were better off,” Isbister says.
In a perfect world, scientists would do a clinical trial. People would be randomly be assigned to one of three groups some would have a blood transfusion, others would be given a placebo and others no transfusion. Scientists would then compare how each group fared. But a trial such as this would never get approved, because why would you give a blood transfusion to someone who didn’t need one, even in a clinical trial setting? Conversely, why risk not giving blood to someone who might well die without it?
“When you’ve got some treatment that’s embedded in medicine … you weren’t going to be able to do trials where you transfused or didn’t transfuse you’d never get through an ethics committee,” Isbister says.
There is one group that have inadvertently served as a sort of test case for non-transfusions.
Jehovah’s Witnesses are known for their opposition to blood transfusions, which is based on edicts from both the Old and New Testaments. As a result, doctors treating Jehovah’s Witnesses have had to take a more cautious approach to their surgical treatment, with surprising results.
“It turned out the patients did better they were doing better because of the better standard of care,” Isbister says.
“They were being prepared better for surgery, [doctors] were fixing up anaemias before surgery, the surgeons weren’t letting people bleed and it changed surgical technique, particularly in cardiac surgery.”
The downsides of blood transfusions
When it comes to teasing out the negative consequences of a blood transfusion, medical researchers have a challenge ahead of them. The reason is that if someone is considered sick enough to need a transfusion, there’s a good chance they’re already in a bad way physically.
This makes it nigh on impossible to say with any degree of certainty that someone’s multi-organ failure or sepsis is caused by the blood transfusion or is the result of the illness and trauma that led to them receiving the blood transfusion in the first place.
What we do know is that the observational studies have pointed to an increase in time spent in hospital, an increased risk of infections after operations (that aren’t directly contracted from the blood itself), increased likelihood of needing artificial ventilation (help with breathing), and an increased risk of landing in intensive care with conditions like multi-organ failure.
Isbister says there’s also the suggestion that the more blood you get, the more problems you are likely to have. (This has been evident even in stable patients, not just those who have had transfusions of massive volumes of blood.) However, even one unit of blood is enough to cause problems.
In an attempt to understand the effects of blood transfusions, Monash University is now running a transfusion registry for anyone who has received more than five units of blood within a six-hour period.
“We’re trying to see what’s happening around Australia in that particular group of patients: what are the reasons for it, what’s going on, what’s happening with their blood.”
Precautionary principle for transfusions
It used to be thought that if a patient needed a unit of blood, you might as well give them two, McJames says, but that has changed completely.
“So the saying in many hospitals now is ‘why give two when one will do’, and that’s even now extended to ‘why give one if none will do’.”
This shift has had significant consequences for surgery and intensive care, says haematologist Dr James Daly, from the Australian and New Zealand Society of Blood Transfusion.
“The anaesthetists and intensivists have been certainly on board and driving this focus on what we call patient blood management, which is really looking to use blood transfusion in the most optimum way,” says Daly, clinical and laboratory haematologist at QML Pathology.
One important change has been to address any underlying anaemia (a deficiency in the number or quality of red blood cells) before any elective surgery. This reduces the likelihood of that a person’s haemoglobin will drop to dangerous levels after surgery.
As well, surgeons are working to minimise blood loss during surgery by using different surgical techniques. In some hospitals, there is also a procedure known as ‘cell salvage’ in which the patient’s own lost blood is carefully collected during surgery, filtered, and transfused back into them.
To transfuse, or not to transfuse?
While there are still unanswered questions on how, when and why blood transfusions are carried out, McJames says there are many medical situations in which a blood transfusion is the only option. And in these situations, it can make the difference between life and death.
The National Blood Authority has overseen the production of a series of evidence-based guidelines on patient blood management, which reflect this changing attitude to transfusion.
“Australia has been very successful over the years on the mantra of ‘give blood, blood saves lives’ and I think that’s in everyone’s psyche and no one questions it.”
Half a million Australians donate blood and McJames says it’s important that we don’t lose sight of the fact that blood transfusions are still life-saving.
“We’ve really got to balance the message very carefully because we don’t want to scare people but equally there is a need for a precautionary approach,” he says.
“You shouldn’t be doing something to a patient if there is no evidence of benefit.”
What does a blood transfusion do to your body?
A growing body of research data from laboratory and animal studies is giving insights into what transfused blood does to the host body.
One clue comes from the fact that blood transfusions were once used to prepare recipients for their kidney transplant, because transfusions were known to reduce the likelihood that the host immune system would reject the donor organ.
This suggests that donor blood is somehow modifying the host’s immune system; a desirable effect in the early days of kidney transplants, but less desirable if you are in intensive care after a car crash and already physically very vulnerable.
The second problem appears to be that storing blood outside the body changes the blood. Chemical messengers called cytokines, and other biological substances, seem to accumulate in stored blood, and there is the possibility that this is causing problems when the blood is transfused into the patient.
“What we do know is the red cell is a much more complicated cell than just carrying haemoglobin around the body for oxygen,” Isbister says.
“Red cells are quite flexible, meant to wriggle its way through capillaries that are half its size and in a lot of settings a stored red cell can’t do that …there is some evidence that it may be that rigid stored red cells cause mischief in the microcirculation.”