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4 Burning Questions About Patient Warming
A skirmish over the science of warming is heating up.
Dan O'Connor
Publish Date: December 1, 2015   |  Tags:   Patient Experience
forced-air warming WINDSWEPT CONTAMINANTS What if the waste heat from forced-air warming spreads airborne contaminants and causes infection?

Of all the questions surrounding patient warming, the most burning is this: Do forced-air warmers circulate contaminants that can cause wound infections, as a spate of recent lawsuits alleges? Read on as we tackle this and other hot topics surrounding your quest to maintain normothermia.

1. Does forced-air warming cause SSIs?
Of the many proven benefits of maintaining normothermia, perhaps the greatest is that it staves off surgical wound infections. But what if the very act of forced-air warming causes SSIs?

You've no doubt heard the claims or seen the ads from law firms trolling for clients: Besides blowing hot air, forced-air warming units stir up the germs from the floor and cause them to go airborne. The jetstream of germs, the notion goes, rises alongside the table and settles over the surface of knee or hip implants in the sterile field. The germs can take root in the wounds and cause debilitating infections, especially in patients undergoing deep joint surgery. Not everyone is buying this (Bunch of) Hot Air Theory.

"Commercially driven junk science that has no basis in reality whatsoever," says an observer.

3M's lawyers say no reputable study has proven that forced-air warmers contaminate the air when they vent their waste heat. Just the opposite is true, they say. Decades of research and clinical experience show that using forced-air to maintain normal body temperature helps reduce the risk of infections and improves surgical outcomes.

"Forced air is highly effective, easy to use, inexpensive and remarkably safe," says anesthesiologist Daniel Sessler, MD, who has researched forced-air warming extensively as chair of the department of outcomes research at the Cleveland Clinic.

3M, which acquired the Bair Hugger as part of its acquisition of Arizant in 2010, is battling lawsuits from more than 50 orthopedic surgery patients who claim that Bair Hugger warming blankets circulated contaminants and caused their SSIs. Plaintiffs' attorneys are angling for a national suit with thousands of plaintiffs.

"3M will vigorously defend the product and the science against these unwarranted lawsuits," says 3M spokeswoman Donna Fleming Runyon. "We think it's unfortunate that the plaintiffs' attorneys are using bad science to blame their clients' infections on a device that has helped so many people."

Bair Hugger has given more comfort to more patients than perhaps any other surgical product. The single-use warming blanket has been used in more than 200 million surgeries since the FDA approved it in 1987. In 2 large randomized trials, patients who were warmed with forced-air blowers showed a reduction in SSIs. So why the onslaught of lawsuits? Just look at who's trying to sully Bair Hugger's sterling safety reputation. That would be Bair Hugger's inventor himself, anesthesiologist Scott Augustine, MD.

3M paid about $800 million in 2010 to acquire the Bair Hugger as part of its acquisition of Arizant. Dr. Augustine resigned as chairman and CEO of Arizant in 2002 and later created a new company, Augustine Temperature Management, which sells a competing warming blanket and mattress called Hot Dog. Similar to an electric blanket, the Hot Dog uses conductive fabric warming rather than forced air to warm surgical patients. Since creating the Hot Dog, Dr. Augustine "has been engaged in a fear-mongering campaign against the Bair Hugger device in an effort to jump-start the sales of his competing product," according to 3M's court filings. Besides disparaging the Bair Hugger system, 3M attorneys also accuse Dr. Augustine of assisting personal injury attorneys in lawsuits against the Bair Hugger.

A source offers his opinion on what's really motivating Dr. Augustine. "Scott's agenda is fueled by revenge. It has nothing to do with patient care. He just wants to take down forced air."

Dr. Augustine doesn't hide his disdain for forced-air warming. He is expected to testify that the device he developed creates an infection risk. Last month, in a small victory for 3M, a federal judge ruled that Dr. Augustine must turn over documents and answer questions about his role in promoting the alleged risks of the Bair Hugger.

hypothermia INTRAOPERATIVE HYPOTHERMIA Even in actively warmed patients, hypothermia is routine during the first hour of anesthesia. Thereafter, average core temperatures progressively increase.

"We didn't recognize the problem when I was running the company and remarkably over 20 years no one else did either," says Dr. Augustine. "About 6 years after I left the company, we accidentally discovered the unintended consequence of forced-air warming."

Dr. Augustine points to 6 studies that have been published in the past 4 years that he says prove forced air's waste heat contamination problem, including one study that showed 2,000 times more airborne particles were present near the surgical site when forced-air warming was used compared to air-free conductive fabric warming. A source familiar with the research is highly skeptical of it. "It's a very abstracted model that doesn't involve real patients or real bacteria," says the source. "All the papers that Scott and his colleagues are quoting are written by his own employees or consultants." In fact, a meta-analysis shows that laminar flow worsens infection risk.

2. Does normothermia really lead to faster discharge?
Yes, and it can be considerable. Researchers at the University of California, San Francisco, discovered that patients who were warmed enough during surgery to maintain normothermia had final intraoperative temperatures 2 ?C higher than patients who were not warmed. Hypothermic patients took about 40 minutes longer to meet discharge criteria, the researchers noted.

3. How common is intraoperative hypothermia?
A lot more common than you may think. While most warmed patients are normothermic by the end of surgery, most patients at least initially experience some intraoperative hypothermia — and it's often prolonged. This is because core-to-peripheral redistribution of body heat precipitously reduces core temperature in the hour after induction of anesthesia, even in actively warmed patients, says Dr. Sessler. Just as all patients experience a small initial decrease in core temperature after induction of general anesthesia, they all recover so that they're normothermic by the end of surgery, he says — so long as you do your part: Actively warm patients during surgery.

An additional strategy is prewarming, actively warming patients for about 30 minutes before induction of anesthesia. "This increases heat content in the body, specifically the tissue temperature in the peripheral thermal compartment," says Dr. Sessler. "Heat can only flow down a temperature gradient. That's how prewarming works. This reduces the gradient, and thus the amount of redistribution.

"People assume that you get more hypothermia with long cases than with short cases," he adds. "In fact the opposite is true. In a short case, you have this redistribution and you don't have time to recover. In longer cases, you have more time to recover and become normothermic. Without active warming, however, a patient's temperature will just go down and down."

4. Is prewarming more important
for shorter cases than for longer ones?

Yes, prewarming is most indicated and effective for shorter cases (less than 60 minutes, induction to emergence). And it's simply a matter of how much time patients' bodies have to warm up. After induction of anesthesia, most patients have an internal redistribution of body heat that slightly reduces their core temperature, explains Dr. Sessler. "This large flow of heat overwhelms even forced air," he says. "But after redistribution is complete, the forced-air warming gradually increases core temperature. The longer the operation, the more time is available for forced air to transfer heat." Put another way: Because core temperature progressively increases after the initial hour of anesthesia, patients having longer operations are more likely to be normothermic at the end of surgery, says Dr. Sessler. Remember the second law of thermodynamics: Heat moves to cold. Although counterintuitive, it is thus more difficult to end with normothermia in shorter than longer cases.