Hypothermia. We typically associate it with being out in the elements; a medical emergency that’s reserved for outdoor adventure seekers or cold-climate construction workers.
But when it comes to the operating room, hypothermia likely isn’t a term that comes to mind.
It turns out that in the OR, avoiding hypothermia and maintaining normothermia – the body’s ideal thermal state – is a really big deal. When patients become hypothermic in surgery, the risk for complications increases, including infections, heart problems or excess bleeding that can lead to blood transfusions that otherwise may not be needed. In fact, research shows that even mild hypothermia can result in significant negative outcomes for patients.
Our bodies are designed to tightly control our internal temperature, no matter what the external temperature is. This natural regulation is called thermoregulation – and it ensures a healthy state of normothermia.
Our core temperature is the temperature of the internal environment of our body, including the heart, lungs, liver and brain. It holds pretty steady around a very cozy 37 degrees Celsius, naturally fluctuating by just a few tenths of a degree throughout the day. This core temperature protects us from more than just feeling cold. When it falls below 36 degrees Celsius, we become hypothermic, and many of our protective, life-sustaining internal mechanisms are diminished or deactivated altogether.
“Almost all of the proteins in the body work very well at 37 degrees Celsius,” says Al Van Duren, global director of scientific affairs for the 3M’s patient warming business. “At temperatures even modestly below or modestly above 37 C, they don’t work well at all. Platelets begin to lose their stickiness; and lymphocytes – the cells in our body that are involved in immunity – stop working well when our temperature drops even slightly.” Since platelets help our blood clot, excess bleeding becomes a serious issue when surgical patients become hypothermic, explains Al. And since our immune cells become diminished, the risk of surgical site infection increases. These are two key examples of a cascade of serious consequences that can occur when our core temperature drops during surgery.
But how do surgical patients become hypothermic? Does it have anything to do with how cold they keep operating rooms?
Not really. As it turns out, anesthesia drugs are the primary culprit.
Life-saving procedures like open-heart surgery, brain surgery or organ transplantation would be impossible without general anesthesia. It’s used when it is important for a patient to be unconscious, as it prevents us from feeling any pain. Anesthesia has made possible countless procedures that improve human health, longevity and quality of life. And although the drugs are usually quite safe for most patients, they do impact one thing in all of us: our ability to regulate core temperature.
Two classes of drugs are used for anesthesia – the ones you inhale and the ones that are given via intravenous infusion. A main side effect of both classes of these drugs is that they cause the redistribution of heat from our core to our periphery.
“People become hypothermic not because they lose heat during surgery,” explains Al. “They become hypothermic primarily because the body’s heat is redistributed from the core to the arms and the legs. The average temperature of the body doesn’t change at all, but the core temperature changes a lot. This is due solely to the drugs used for anesthesia.”
Hypothermia can be avoided during surgery.
Maintaining a constant ideal core temperature (normothermia) has long been identified as a key method of fighting the negative patient outcomes that can come from hypothermia, including surgical site infections, excess bleeding and cardiac disturbances. And study after study has shown that forced-air warming is an effective method for preventing and treating unintended hypothermia. In fact, the clinical benefits, safety and effectiveness of forced-air warming has been documented in more than 170 studies and more than 60 randomized controlled clinical trials. When a patient’s temperature is monitored and an active warming measure is introduced before (preoperatively), during (intraoperatively) and after surgery (postoperatively), the likelihood of a core temperature drop decreases.
Forced-air warming is typically delivered via a special blanket or a gown that’s placed on or under the patient throughout the surgical process. Utilizing the properties of convection and radiation, warm air travels through consistent, evenly distributed perforations in the soft material, transferring heat across the surface of the patient’s skin.
After the patient has been pre-warmed, or warmed prior to anesthesia, intraoperative warming measures are taken, which decrease the amount of heat loss that occurs during surgery and help maintain core temperature. Postoperatively, forced air warming typically is used to restore thermal comfort to the patient. Pre-warming is an important, sometimes overlooked step in combatting unintended hypothermia, says Al.
“Before anesthesia-induced redistribution occurs, skin temperature is low, so it’s easier to transfer heat into patients,” says Al. “We encourage clinicians to pre-warm patients while they’re awake, and that way, after they have anesthesia and redistribution occurs, patients already are warmed up so that their core temperature doesn’t decrease very much.”
One study found that a short, aggressive period of pre-warming is very effective – even as few as 10 minutes can be enough. From a patient perspective, the pre-warming phase can be a bit uncomfortable, as heat is being added when their bodies are already normothermic. That’s why a brief, intense period often is all that’s needed.
But what patients really seem to remember about their surgery, in terms of comfort, is how cold they can feel afterward. When they wake up from surgery, most patients often expect to feel pain, but many don’t expect to feel so cold.
“Postoperatively, thermal comfort is the one thing patients seem to remember for years after they’ve had surgery,” he says. “Thermal comfort is a really important outcome to patients, and rightly so – it does not feel good to shiver. But, what often goes unrecognized is that maintaining normothermia intraoperatively prevented really serious outcomes that they didn’t even know about like infection and bleeding.”
Hypothermia can easily be prevented throughout the surgical process. And keeping people warm during surgery can reduce the risk of infections, reduce the length of hospital stays and improve overall outcomes from surgery.
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