Patient Warming: The Inside Story

by Scott D. Augustine MD, Augustine Temperature Management

October 15, 2015

 Almost 30 years ago, I invented a forced-air warming system for surgical patients and introduced it to the medical world.  Now, I am proclaiming that forced-air warming, in certain circumstances, is a danger to patients.  Given the irony, I thought some people might be interested in the full story.

 I was a new anesthesia resident at the Naval Hospital in San Diego when I first encountered perioperative hypothermia. Nearly all patients were clinically hypothermic on admission to the recovery room in 1981, and no one thought twice about it.  Despite using all available patient warming equipment (i.e. water mattresses, airway heaters, and fluid warmers) hypothermia was ubiquitous and considered an accepted part of surgery.

I started asking postoperative patients and found that “freezing to death” was the most memorable aspect of surgery.  My interest was piqued.

What was clear from the literature is that under anesthesia, general or conduction anesthesia, we all become poikilothermic.  Just like the reptiles, we gain or lose heat depending on the environmental temperature.  The challenge was obvious: how to produce a warm environment around a patient without requiring the whole room to be warm, as was the common practice in pediatric surgery.

During my spare time as a resident, I started working on an inflatable air blanket that would wrap around the patient and circulate warm air. The first prototypes were very crude and made of plastic sheets that were heat-sealed together using a clothes iron. The first blower was a hairdryer. It took a lot of prototyping and refining, but by 1988 forced-air warming (FAW) was launched in recovery rooms across America.

It was a good product that solved a need.  The “need” morphed from simply providing thermal comfort to avoiding the many recently documented negative physiological effects of hypothermia.  Hundreds of published studies demonstrated that mild hypothermia had an adverse effect on nearly everything that we studied: increased soft tissue wound infections, increased bleeding, increased adverse cardiac events, increased mortality, and increased hospital stays among other things.

FAW changed surgical practice and measurably improved the outcomes of hundreds of millions of surgical patients over the past 25 years.

I left Augustine Medical (renamed Arizant) at the end of 2002. Arizant was subsequently sold to a private equity firm and later to 3M.  After sitting out my two-year non-compete, I formed a product development company with no intention of getting back into patient warming. We were working on reliably producing a bubble of HEPA-clean air over a pillow for allergy and asthma reduction when we stumbled on the FAW waste heat rising phenomena.

Forced-air systems produce 1000 watts of heat at 40 ft/m3. Convective heat transfer is not particularly efficient, so only about 50 watts of the heated air gets transferred to the patient. We learned that there is a significant unintended consequence of that waste heat. The remaining 950 watts of waste hot air vents near the floor, heats the contaminated air resident near the floor, and then rises alongside the table into the sterile surgical field carrying contaminants with it.

For 18 months we studied the rising waste heat from every angle.  Bottom line–the waste heat rises 100% of the time, which is not surprising since it is a basic principle of physics.

Even though I had been gone from the Company for six years, I was feeling terribly responsible for the unintended consequences of my invention.  Digging into the research, we found that while soft tissue infections require contamination of over 1 million bacteria, the biofilm that can form on implanted material allows a single airborne bacterium to cause a devastating periprosthetic joint infection.  Clearly implant patients, especially orthopedic implant patients, were the “at-risk” group.

The fact that a problem turned up with forced air warming after 20 years on the market is certainly not unheard of in the medical device or pharmaceutical industries.  For example, Cox-2 NSAIDs—after many years on the market–now carry a “black box” warning to not use if you have coronary artery disease.  They are still very good drugs, just don’t use them if you’ve got heart problems.  Similarly, I believe that forced-air warming should have a “black box” warning: “do not use in implant surgery, especially orthopedic implant surgery.”

I became a doctor to help patients, not hurt them. I have the same motivation as an inventor, so I invented a safe alternative to FAW:  air-free HotDog® patient warming. It’s the only warming system that can warm from above and below the patient simultaneously, which is far more effective than either above or below individually. HotDog® uses conductive fabric to deliver safe, even warmth—no blowing air or water—resulting is a uniquely versatile, more effective warming solution.

Over the next short while, six independent studies were published corroborating our research showing that the rising waste forced air heat contaminates the sterile surgical field with contaminants from the floor.  One study by Legg et al showed 2000 times more contaminating particles in the air above the surgical site with FAW than with HotDog® warming.  McGovern et al published their study showing that their deep joint infection rates dropped 74% (1437 patients, 2.5 years, p=0.028) when they discontinued FAW in orthopedics. They switched to HotDog® for safely maintaining normothermia.

I let the manufacturer know about the problem with FAW, urging them to take action, offering business collaborations.   Their response was massively negative. The more research that was published showing contamination and infection risk, the more adamant their denials.  They have no credible research to refute the published waste heat studies—zero studies. With no research to promote, they instead decided to start a personal smear campaign against me and the HotDog® product, as if that could possibly solve their problem.

A company can obfuscate, confuse and mislead for awhile, but eventually their customers and plaintiffs lawyers catch on.  About two years ago, a law firm out of Houston filed two product liability lawsuits against that FAW manufacturer alleging that their clients’ devastating knee infections were caused by the waste heat from FAW. By August 2015, a Google search of “FAW infections” revealed over 100 law firms advertising for injured joint implant patients.  Many of these firms are also advertising on TV.  These mass tort lawyers are well funded and seem to be very well organized.  They have already filed for Multidistrict Litigation (MDL) certification in Federal Court. It is reasonable to assume that there could be tens of thousands of plaintiffs.

We at ATM are just 3rd party bystanders watching the litigation show.  While I feel terrible that my invention is causing catastrophic infections, I also feel that I’ve done everything that I could reasonably do to warn both the FAW manufacturer and the medical community.  FAW remains a useful tool, just not in ultra-clean surgeries like orthopedics. That is where air-free warming is the safer alternative.

Dr. Augustine is a retired Anesthesiologist and inventor of the HotDog® Warming System.