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What Is a Blood Warmer?

Mary McMahon
Updated Mar 03, 2024
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A blood warmer heats blood or fluids prior to transfusion into a patient. It can be used when there are concerns about transfusing a large volume of cold fluids. This could be necessary in cases where patients have experienced massive trauma and need large transfusions, or when they are fragile for medical reasons. Once a patient’s body has started to cool, however, a blood warmer will not offer significant benefits; it is designed to prevent heat loss, not to reverse it.

The device holds an infusion bag of blood, fluids, or solutions and heats it to a set point that will be safe for the patient before running it through an infusion pump. Nurses and technicians can control the temperature as well as the infusion rate. Blood warmers can be used in emergency settings, operating rooms, and intensive care units to provide warm blood and fluids to patients who need them, and a hospital may keep multiple warmers on a floor to ensure one will always be available.

Using a blood warmer is indicated when more than 50% of the patient’s fluid volume is going to be replaced with a transfusion, or when blood is going to be infused very rapidly. Another consideration can be in surgery where several units of blood are necessary, and more might be needed later. To reduce the risk that the patient develops hypothermia from too many units of cold blood, a blood warmer can be used. It is important to set up the warmer in advance, because it needs some time to work, so if nurses think one might be needed, they may start pre-warming it to make it readily available.

Instead of using a blood warmer to address concerns about possible heat loss, other options can include warming blankets or pads for the patient. These warm the whole body to offset hypothermia and keep the patient warm and comfortable. For patients who are at risk of developing hypothermia because of their medical condition, simply warming fluids may not be enough, and these measures could be more appropriate.

Once hypothermia sets in, the patient needs to be warmed by other measures. Infusing warm fluids will not help the patient warm up, although they can be part of treatment to prevent further heat loss as the patient is treated. Hypothermia care can involve slowly raising the patient’s temperature to prevent complications, using a variety of means.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By croydon — On Jul 20, 2014

@Fa5t3r - They wouldn't really be able to heat the blood returning to the body to the point where it would be able to add much heat to the body, I would think. If they heat it too much they would essentially cook it and make it useless. Just putting it at average body temperature isn't going to do much, since blood is funneled through so many different vessels it would quickly return to whatever temperature the body is at the time.

If they really need to warm someone up, they would do it with heating blankets and packs, not by manipulating their blood. It's a little bit inefficient to warm someone from the outside in, but it's the safest way.

By Fa5t3r — On Jul 20, 2014

@umbra21 - The body is fairly good at warming you up if you need it, which is why they don't always have to bother. I often give plasma and I don't think they heat it back up when they return the blood cells. And it must get cool from being spun in the centrifuge to separate the components of the blood.

I imagine it's only a problem if they have to give someone a lot of blood, or maybe if the person is already cold and needs to be reheated.

By umbra21 — On Jul 20, 2014

I always find it a bit weird how warm blood is when you donate it. When the tube lies against my arm it feels significantly warmer than my skin. So it's not surprising that they might need to warm up blood before putting it into someone. I imagine hospitals are quite cold in general and blood is probably kept even cooler in order to preserve it. It could be a huge shock to be given very cold blood, especially if you are already injured or sick.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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