Normothermic Machine Perfusion (NMP)

Medically reviewed by James F. Trotter, MD and Joseph S. Redman, MD, PhD, National Friends Medical Advisory Board · Last reviewed October 1, 2026

NMP keeps a donor liver warm, oxygenated and working on a machine instead of on ice. Here is how it works, what trials show and what to ask.

NMP keeps a donor liver oxygenated and metabolically active outside the body, instead of preserving it on ice (cold storage). The liver is connected to a device that pumps warm, oxygen-rich, blood-based fluid through it, mimicking the body's own circulation. Some devices are portable and run during transport from the donor hospital.

What NMP is, in plain words

"Normothermic" means "normal temperature" — body temperature. On the machine, the liver is kept close to how it would be inside a person. It gets oxygen and nutrients, and it keeps doing its job: it makes bile and clears waste from the fluid.

That is very different from cold storage, where the liver sits in a cooler of preservation fluid and ice. Cold slows the liver down, but the liver gets no oxygen and the team can't see how well it is working until it is in the recipient.

Why this matters for transplant patients

Older or marginal donor livers become safer to use. Cold storage stresses these livers more; NMP preserves and lets the team assess function before committing to the transplant. Because the liver is working on the machine, the team can watch signs like bile production and how well it clears lactate (a waste product). See extended criteria donors.
Surgical scheduling is more flexible. Cold storage forces a fast clock; NMP buys hours, which can mean better-prepared OR teams.
Fewer biliary complications in some studies. A large U.S. trial found fewer bile duct injuries with NMP (details below), while an earlier European trial found no clear difference. Results depend on the device, the type of donor and how the team uses it.

What the research shows

Two large randomized trials compared NMP with standard cold storage.

European trial (Nature, 2018), 220 liver transplants. Compared with cold storage, NMP was linked to:

50% less liver injury, measured by liver enzymes released after transplant
50% fewer donor livers thrown away (discarded)
54% longer average preservation time

There was no significant difference in bile duct complications, survival of the new liver or survival of the patient.

U.S. trial (JAMA Surgery, 2022), 300 recipients at 20 U.S. programs. The device was started at the donor hospital and ran during transport. Compared with cold storage:

A slow start for the new liver (early allograft dysfunction) happened in about 18 out of 100 patients with NMP vs. about 31 out of 100 with cold storage.
Bile duct injury from lack of blood flow (ischemic biliary complications) at 12 months happened in about 3 out of 100 vs. about 10 out of 100.
Livers from cardiac-death donors were used about twice as often — 51% vs. 26%.

National data now reflects this. The OPTN/SRTR 2023 Annual Data Report linked record transplant numbers partly to more livers from older and DCD donors, likely related to wider use of machine perfusion. See our article on DCD vs. brain-death donors.

The devices

Two FDA-approved devices are commonly cited: OrganOx Metra and TransMedics OCS. The companion article OrganOx vs. TransMedics covers the device differences caregivers ask about. Some programs also use cold perfusion instead of, or before, warm perfusion — see HOPE perfusion.

How NMP affects a patient on the list

Your priority doesn't change. Offers still come to you based on your MELD score, blood type, size and distance from the donor hospital. NMP changes which livers your center can safely accept, not where you are in line. Learn how the liver waiting list works.
More usable offers. A center with an active NMP program may be able to accept livers other centers decline, which may shorten the wait.
Possible extra cost questions. Machine perfusion may add cost. Ask your financial coordinator whether your insurance treats it differently — see why you always have to call.

Questions to ask your transplant team

If you are evaluating centers, ask whether they have an active NMP program, which device(s) they use, and how often they accept livers that needed NMP to be transplantable. Other good questions:

"Do you start NMP at the donor hospital, or after the liver arrives here?"
"What do you check on the machine before deciding to use a liver?"
"Would you use a liver that needed NMP for me?"
"Does using a perfused liver change my care or follow-up after transplant?"

Common misconceptions

"NMP repairs any damaged liver." It can protect a liver and show how it is working, but some livers are still turned down after testing. That is the system working.
"Being on a machine means it's a worse liver." Not always. Teams also use NMP for good livers to protect them and allow better scheduling.
"All centers have this." They don't. Compare programs on our center comparison map.

Sources

Educational only. Not medical advice. Your transplant team has the final word.

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