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The Case for Fluid Warming
It's an underused and highly effective way to maintain normothermia.
Charles Smith
Publish Date: March 31, 2015   |  Tags:   Patient Experience
fluid warmer TURN IT ON The best time to get your fluid warmer up and running is before the case begins.

If you're not already doing it, here's something to add to the checklist when you're turning over the OR: Turn on the fluid warmer. It takes only a few minutes for fluids to reach that just-right Goldilocks temperature, and it's an easy, cost-effective way to help ensure patient normothermia.

In the 25-plus years I've been administering anesthesia, I've found fluid warming to be the most effective technique for keeping patients normothermic during the entire case. It works for inpatient procedures, outpatient procedures, trauma, small surgeries, big surgeries — anything that requires general anesthesia. It even works with Caesarean sections using spinals or epidurals. And when you combine fluid warming with convective warming, you can practically guarantee that patients won't get cold during surgery.

So why aren't more people taking advantage of this useful technique? From what I've seen, the mistake many make is waiting too long. Oftentimes, people don't think of it, or they think of it after anesthesia induction. But once you've started induction, you're committed to concentrating on airway management, patient positioning and getting the patient ready for the surgical incision. So the best time to think of it is before you put the patient to sleep. My rule of thumb is, for any patient who's going to require at least a liter of fluid, I make sure the fluid warmer is connected before induction of anesthesia, and before any physiological changes start to take place.

That doesn't mean you should never start fluid warming after a case has begun. Even if you wait until after you've given a liter of fluid and then decide you'd better start the fluid warmer because the surgery is lasting longer than expected, that's OK. But, by that time you've missed a great opportunity to use it for the entire case.

An Important Degree of Difference

How do we know fluid warming works? Some years back I led a study (tinyurl.com/orgoeuf) of 38 women undergoing elective gynecological surgery. The women were randomized into 2 groups. One group was given fluid warmed to 42 degrees (Celsius); the other group received room-temperature fluid (about 21 degrees). All 38 were given general anesthesia with isoflurane and all had standard operating room blankets and surgical drapes.

We measured core temperatures at induction and then at 15-minute intervals after induction. The result: The warm-fluid group had higher core temperatures at the end of surgery (36.2 degrees vs. 35.6 degrees). Also 35% of the room temperature group had final core temperatures below 35.5 degrees, compared with none in the warm-fluid group.

There was no difference in patient outcomes in this relatively small sample, but we know that patients who experience hypothermia are more susceptible to infections and less likely to be satisfied with their surgical experience. Fluid warming, combined with other heat-conservation methods, clearly helps maintain normothermia.

— Charles E. Smith, MD

Safe and effective
The fluid-warming technology available today is incredibly good. When I started out in anesthesia, the warmers that were available didn't warm adequately, so by the time the fluid got into the patient's body, it was usually closer to room temperature than to the temperature of the patient.

By contrast, the generation we're using now warms fluids to 41 degrees (Celsius) in the heating element and lets you deliver it to the patient at 36 to 37 degrees.

You should be aware that flow rates can affect the amount of cooling that takes place before fluid reaches the patient. (Typical rates for an anesthesiologist during induction are about 25 mLs per minute). But if you're dealing with a patient who's in shock, who's hemorrhaging or who need fluids rapidly, flow rate might be much faster — more like 100 to 300 mLs per minute. With slow and moderate flow rates, which many anesthesiologists use, there can be a significant cool-down. With a faster flow rate, there's very little chance of having that cool-down. Those faster rates aren't commonly needed in outpatient surgery, but they can be, and you'd need to use different fluid warmers in those scenarios.

The best ways to mitigate heat loss after it exits the fluid warmer are to either go with a fluid warmer that warms fluid all the way until it reaches the patient's IV, or else to have the fluid warmer in line very close to the patient's IV. Some manufacturers have mechanisms that ensure there is no cool-down before fluid reaches the patient.

Is there a chance the fluid you're getting ready to deliver to the patient will ever be too warm? It doesn't happen very often, and all the warmers marketed today have safety mechanisms, so they'll alarm if they're over temperature and turn themselves off. If you're buying something that's produced in the U.S., you can be confident it will have that feature.

One more weapon
It's well established that the period just after induction — known as redistribution — is when patients are most at risk for losing substantial body heat. Redistribution hypothermia is a result of the vasodilated state brought on by anesthesia. Body heat is redistributed from the core to the periphery and ultimately lost to the environment, unless various mechanisms are used to combat loss.

One way to fight heat loss is to keep the operating room warmer than normal during that time, but that idea is likely to generate some pushback from nurses and surgeons wearing multiple layers of gowns. And the resistance may be especially strong in outpatient surgery, where one of the goals is fast surgery and fast turnover.

But if you keep the room fairly cool, and then you administer cold fluids, it's a further thermal insult to the patient, and it's likely to result in a substantial decrease in core temperature. Warm fluids, on the other hand, reduce the likelihood of significant hypothermia. It's one of the more effective chill-fighting weapons to keep in your arsenal.

Incidentally, warming patients with convective warmers in pre-op can also be effective, but in our experience, it's not as conducive to patient throughput as fluid warming.

patients given warmed fluids JUST RIGHT Patients given warmed fluids typically have higher core temperatures at the end of surgery.

Price is right
The bottom line is that fluid warming is easy to do, the equipment doesn't cost very much — in fact, the price has come down markedly — and it's highly effective.

There are numerous manufacturers and models available, with some minor differences, but essentially they all do the same thing. As noted, you need to look at the temperature of the fluid that's going to be delivered to the patient, based on your typical flow rates, and choose a model that fits your needs. Pricing and ergonomics are the other considerations. The end users — the OR staff — have to be comfortable putting the warmer together and using it the way the manufacturer recommends, since every system is a little different.

The best thing to do is to trial any machine you're considering and to answer 2 questions: Does it do what you expect it to do? And will people use it? In other words, is it easy enough to set up and make part of the routine? It should be easy to turn on and off, easy to install, easy to clean, easy to use, and of course, safe, reliable and efficient.