Innovative technology could dramatically increase the number of livers that can be donated.

Posted on: 8th September 2023

With so many people on the waiting list it is vital that every suitable donated liver gets to a recipient.

Technology called normothermic regional perfusion (NRP) could dramatically increase the number of livers available. And mean they work better after transplant. But it is not available in all hospitals.

The British Liver Trust is campaigning on behalf of patients to try and ensure NRP is funded throughout the NHS. So that more livers can be used for transplantation.

When liver transplantation began in the UK in 1968, donated livers had to be used quickly. As soon as a liver became available the person receiving it had to get to the donor’s hospital. The two would need to be in next door operating theatres. Unfortunately, many precious donated livers could not be transplanted in time.

In 1988, a British surgeon showed that it was possible to keep livers out of the body for many hours. By flushing a special ice-cold liquid through them before they were removed. Such liquids are called preservation solutions.

Recent research has continued to improve how livers can be preserved for transplantation.

The two types of organ donor

There are two main types of liver donor.

Most donated livers come from people who have died. For a liver to be transplanted the donor must have died in hospital from some kind of terrible brain injury. For example a stroke, or a head trauma from an accident.

Donation after brain death donors (DBD). Are people who have been declared dead after tests of their brain show no function. They stay on a breathing machine (ventilator). So their heart carries on beating. Their organs, including their liver, continue to get blood and oxygen until they are removed.

Donors after circulatory death, (DCD). These donors used to be called non-heart-beating donors. For some reason it is either not appropriate or not possible to perform brain tests on these donors. Instead they are declared dead when their heart stops beating. Usually after a decision to stop treatment and take them off a ventilator.

Surgeons used to be very cautious about using livers from DCD donors.

DCD organs have a period of time between their heart stopping and their organs being cooled down. During this time the cells in the organs are still trying to work. But because they are not getting oxygen, they start to use up their energy supplies. The longer the organs are warm, the more their energy stores are run down.

Cooling the organs slows down the rate that energy stores are drained. But does not stop it. There is a point of no return when the cells run out of energy and stop working. The longer an organ is stored, the less likely it is to work after it is transplanted.

When it is unclear how well a liver will work after transplant doctors may decide not to risk using it.

Perfusion technology - saving more DCD livers.

Perfusion technology uses machines to keep oxygen pumping through a donor liver. It can let the liver recover. And in some cases remove the uncertainty about how well a donated liver will work.

NRP (In situ normothermic regional perfusion)

The gold standard is NRP. An NRP machine pumps blood around the organs while they are still in the donor’s tummy. This blood carries oxygen. So the cells in the organs can recharge their energy stores. While this is happening doctors can run tests on the donor liver. So they can find out if it is likely to work well after transplant.

This means many more DCD livers can be transplanted when NRP is used.

It usually takes a couple of hours for the organs to recover. After this the preservation fluid is flushed through them. Then surgeons can remove the liver and pack it in ice to be taken to the recipient’s hospital.

Other types of perfusion technology

There are also two types of perfusion machine that work once the donor liver has been removed. These are called “Ex situ machine perfusion”. They can also help livers recover. But they are more expensive than NRP. They are usually done once the liver arrives at the recipient’s hospital.

Hypothermic oxygenated machine perfusion (HOPE). Pumps a small amount of oxygen mixed with cold preservation liquid around the liver. Because the liver is cold, its cells are not very active. So only a small amount of oxygen is needed to slowly recharge the energy stores. But it is not possible to run tests on a liver using this technique.

Normothermic machine perfusion, (NMP). Pumps blood around the liver at normal body temperature. This means the liver can recover and some tests can be done on it.

Machine perfusion is rapidly changing how donor livers are managed in the UK. But it is not available for all potential donors.

Professor Chris Watson of Cambridge University Hospitals NHS Foundation Trust said:

“The bottom line is that NRP results in many more livers transplanted, with better outcomes. If the 527 non-NRP donors last year had the same transplant rate as the NRP donors, it would have resulted in 163 more livers”.