Study Links Forced-air Warming to Infections: 3.8x Increase In Orthopedic Implant Cases

Previously, research studying the effects of forced-air warming on laminar flow operating theaters was limited to contamination…until now.

The use of forced-air warming during orthopedic implant surgery was associated with a 3.8 times increase in deep joint infections as compared to warming patients with HotDog patient warming, according to a newly published study.

The study, published in the November issue of the Journal of Bone and Joint Surgery (Br), was conducted by orthopedic surgeons at Northumbria Healthcare Trust in the United Kingdom. Reviewing hip replacement surgeries performed on 1,437 patients over 2.5 years, the study compared the incidence of deep joint infections on patients warmed with 3M’s Bair Hugger® forced-air system with those warmed with the air-free HotDog® system. Patients warmed with the Bair Hugger system suffered deep joint infections at a rate of 3.1%; with the HotDog system, the infection rate dropped to 0.8%.

“A 74% percent reduction in implant infections is incredibly significant,” said Dr. Scott Augustine, anesthesiologist and CEO of Augustine Temperature Management, manufacturer of HotDog warming. “Every joint infection is a disaster—both for the patient and the system. The process is horrific: ex-plant the joint, prolonged hospitalization, 6-8 weeks of IV antibiotics and then—assuming no amputation—re-plant the joint. The average cost is around $100,000.”

“Based on this study,” Dr. Augustine said, “switching from forced-air to HotDog warming could save hundreds of millions in medical costs—and reduce suffering for thousands of patients.” Dr. Augustine is the inventor of both HotDog warming and the Bair Hugger system.

According to the authors of the study, the higher rates of infection were associated with the disruption of operating room ventilation by the forced-air blowers: “Excess heat from FAW [forced air] resulted in the development of hot-air convection currents between the surgeon’s body and the operating table, that transported [contaminated] floor-level air upwards and into the surgical site.”

As a result, the authors concluded: “Air-free warming is, therefore, recommended over forced-air warming for orthopedic procedures.”

Citation:

McGovern P.D., et al: J. Bone and Joint Surgery Br, Vol. 93-B, Issue 11, pp 1537-44. Nov. 2011.

Note: Augustine Temperature Management provided no funding to support the study. One of the study’s authors, Mark Albrecht, has been an employee of Augustine Biomedical + Design and is currently on a Fellowship from the company, pursuing a masters in statistics at the University of Minnesota. This relationship was revealed in the study by the following: “The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article.” Other than this relationship, our company had no financial connection to the study whatsoever.

FAW's Impact on SSIs

“How can forced-air warming be unsafe when research shows that it reduces infections?”

This is a common question, and the best explanation was given by Yale scientist Dr. Marc Abreu in the October 2010 Anesthesiology News Review. In the article, titled New Concepts in Perioperative Temperature Management: Monitoring and Management, Dr. Abreu wrote that, “…any potential airborne contamination caused by FAW waste heat must have a negligible effect on soft tissue SSIs. However, patients undergoing surgery involving implanted foreign materials, especially for orthopedics, may be at higher risk for infection from airborne contamination.” (emphasis added)

The risk of infection with FAW, at least as established so far, is specific to ultra-clean surgeries involving implanted foreign materials: orthopedics, neuro, and cardiac. There is a fundamental difference in causation between soft-tissue infections and surgical infections involving implanted foreign materials—and that is the point commonly missed.

In a seminal article published in 1996, Kurz showed that FAW decreases the SSI rate by a factor of 3x in soft tissue, colon surgery.(1) This narrow finding has been generalized to the belief that all patients treated with FAW are at a lower risk for infections for all surgeries.

The error is in the generalization of Kurz’s very specific data: research specific to soft tissue wound infections in colon surgery has been illogically generalized to apply to all wound infections. The Kurz study is excellent work, however the causative mechanisms for soft tissue infections are fundamentally different than for deep joint infections.

Soft Tissue Infections:
It takes more than 10,000 bacteria contaminating a wound to cause a soft tissue infection, and those bacteria usually get into the wound from the adjacent skin or from cut bowel. The Kurz study certainly validates that normothermic patients have fewer soft tissue infections, and it probably does not matter if the warming technique (FAW) also contaminates the air above the wound: it’s difficult to get 10,000 bacteria into an open wound by the airborne route.

Deep Joint Infections:
In contrast, it takes only a single bacterium to infect a new prosthetic joint (and probably any other surgery involving implanted foreign materials), and that bacterium usually gets into the wound by the airborne route.(2,3) The Kurz study does not address this situation. Once the bacterium lands on the implanted foreign material, it encapsulates itself in biofilm, which protects it from both antibiotics and antibodies. In contrast, the bacteria in soft tissue wounds cannot form effective biofilms.

Until recently, deep orthopedic infection rates during FAW had never been formally studied. Considering the fundamentally different mechanism of causation, the safety of FAW during implant surgery cannot be assumed from a soft tissue infection study such as Kurz’s.

A new study involving 1437 patients over 2.5 years, has finally addressed this issue. The conclusion:

“[Bair Hugger®] Patient warming ventilation disruption was associated with a significant increase in deep joint infections, as demonstrated by an elevated infection odds-ratio (3.8, p=0.028) for the forced air versus conductive fabric patient groups (n=1437 cases, 2.5-year period).”(4) (emphasis added)

To put it more simply: Patients warmed with Bair Hugger suffered 3.8 times as many deep joint infections as those warmed with the HotDog air-free system.

In surgeries that involve implanted materials, especially orthopedic implants such as knees and hips, the new research shows that FAW increases deep joint infections, as compared to other warming modalities that do not blow hot, contaminated air.

The long-held assumption that FAW decreases SSIs is simply not valid for implant surgery.

References:
1. Kurz A, et al. Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. NEJM. 1996; 334:1209-1215.
2. Whyte W. The role of clothing and drapes in the operating room. J. Hosp. Infect. 1988 May; 11 Suppl C:2-17.
3. Mangram AJ, Horan TC, Pearson ML, Silver LC, Jarvis WR. Guideline for Prevention of Surgical Site Infection, 1999. Centers for Disease Control and Prevention (CDC) Hospital Infection Control Practices Advisory Committee. Am J Infect Control. 1999 Apr;27(2):97-132; quiz 133-134; discussion 96.
4. Forced Air Warming and Ultra-Clean Ventilation Do Not Mix: An Investigation of Theatre Ventilation, Patient Warming and Joint Replacement Infection in Orthopedics. Study accepted for publication in a major orthopedic surgery journal, November 2011.

Latest Evidence of Forced-Air Contamination -- Must See

Here is the latest evidence of forced-air warming units contaminating the operating room by overcoming protective laminar flow ventilation. The room temperature tracer particles and bubbles are neutrally buoyant, which is to say they follow the air currents of the room. When forced-air warming units dump 900 watts of waste heat into the operating room, it is no surprise that we can visualize the effects: heat rises. Notice the laminar flow working properly with conductive fabric warming, or with forced-air "Heat OFF" as control. Then with "Heat ON" watch the stunning evidence of forced-air waste heat mobilizing air from the dirty floor and sending it right up into the surgical site, contaminating it. The evidence speaks for itself: as hot air rises, so does risk.

The Northumbria orthopedic team has set up their own blog to show their findings. With patient safety in mind, they have compiled excellent research and the visual evidence is stunning. To access their blog, click on the following link: www.northumbriaorthopaedics.blogspot.com

Laminar vs. Conventional Ventilation

Common Question: “My OR doesn’t use laminar flow. Does waste hot air still matter?”

Answer: Absolutely. Consider the following:

What is laminar ventilation and what is conventional ventilation?

Operating room air is typically introduced from the ceiling, moves towards the floor, and exits through the side vents. US standards for hospital construction require that operating room ventilation be filtered, at a minimum, to an efficiency of >90% for the removal of germ sized particles. Many ventilation systems do much better than that, by employing High Efficiency Particulate Air filtration commonly known as HEPA, which by definition removes >99.97% of germ sized particles from the airflow.

Conventional Ventilation	Laminar Ventilation (Ultra-clean)
Air filtration less than HEPA	Air filtration is HEPA (99.97%)
Downward air current is non-uniform	Uniform, high-velocity air current
Multiple ceiling vents, angles, and velocities	Uniformity minimizes turbulence
Creates significant turbulence in the ventilation air	Unless disrupted, eliminates contaminant mobilization into the sterile field

Why does our research focus on laminar flow ventilation?

It’s difficult to visually show the effects of waste heat with either tracer particles or neutral buoyancy bubbles in conventional ventilation operating rooms because the turbulent air-currents disrupt the visual patterns.


What types of procedures are most impacted by rising hot air?

Whether a surgery is performed under laminar flow ventilation or conventional ventilation, it only takes one germ to infect a wound when prosthetic devices are implanted. Therefore, avoiding contaminating the sterile field with rising hot air is most important in orthopedic, cardiac, or other implant surgeries. Blowing contaminated air into the surgical site should not be tolerated during such procedures.


Does waste heat matter during general surgery with conventional ventilation?

Yes. Although the risks and consequences are much greater in ultra-clean implant surgery, you still don’t want germs blowing around the surgical site under any circumstances. A recent study in the American Journal of Infection Control titled “Forced-air warming blowers: An evaluation of filtration adequacy and airborne contamination emission in the operating room,” found:
• 58% of blowers were generating significant levels of particles downstream of the intake filter. The authors theorized that this may be related to the release of built- up contaminants acquired during previous periods of use.
• 92% of FAW blowers showed viable microorganism growth from air path swabs, including MRSA.

Stay tuned for more videos…

Posting in "Controversies in Hospital Infection Prevention" Blog

An infectious diseases expert from Richmond, Virginia posted information on his blog about the contamination risk of forced-air warming devices. The blog, titled, "Controversies in Hospital Infection Prevention" had this to say:

Bair Hugger vs HotDog
This morning's New York Times business section has an article about Dr. Scott Augustine, the inventor of the Bair Hugger, a device used in the operating room that uses forced air to keep patients warm so as to reduce postoperative infections. Perioperative warming is one of the Surgical Care Improvement Project (SCIP) metrics. The Bair Hugger is now made by Arizant and Dr. Augustine no longer has any connection to the product. He has invented a new warming product that uses conductive fabric, called the HotDog warmer, and now claims that the Bair Hugger causes infections. The New York Times article points out that there may be some theoretical concerns for infection caused by the Bair Hugger, but no definitive evidence.

We shared a new video with Dr. Edmond that is a snippet from a new CEU presentation that will soon be available about airflow disruptions in the operating room.

Addendum 12/30/10:
Dr. Scott Augustine emailed me about this posting and included a video which allows you to visualize the air currents when a forced air warming device is used. It's worth viewing and I think demonstrates plausibility for increased infection risk.

Latest Laminar Disruption Evidence -- Stunning

Here is yet more clear evidence from the Northumbria orthopedic team, of forced-air warming units disrupting protective laminar flow ventilation. The tracer bubbles are neutrally buoyant, which is to say they follow the air currents of the room. Notice the laminar flow working properly with conductive fabric warming. Then watch the stunning evidence of forced-air waste heat mobilizing air from the dirty floor and sending it right up into the surgical site, contaminating it. The evidence speaks for itself: as hot air rises, so does risk.

The Northumbria orthopedic team has set up their own blog to show their findings. With patient safety in mind, they have compiled excellent research and the visual evidence is stunning. To access their blog, click on the following link: www.northumbriaorthopaedics.blogspot.com

More Evidence of Forced-Air Disrupting Protective Laminar Flow

Here is more clear evidence from the Northumbria orthopedic team, of forced-air warming units disrupting protective laminar flow ventilation. As you can see in the video, the addition of normal operating room factors like operating lights, and even an anesthetist, can increase the negative impact of forced-air blowers on proper laminar flow.

This evidence begs the question: should normal operating room procedures be held captive by the fickle whims of the waste heat air currents from forced-air warming units? Now there is an alternative. Free your operating room, replace the forced-air warming units: with non-disruptive, air-free conductive fabric warming.

The Northumbria orthopedic team has set up their own blog to show their findings. With patient safety in mind, they have compiled excellent research and the visual evidence is stunning. To access their blog, click on the following link: www.northumbriaorthopaedics.blogspot.com

Laminar Disruption: Forced-Air Compared to Conductive Fabric Warming

The orthopedic team at Northumbria Healthcare NHS Trust in the UK has shown a great interest in the effects of air movement in laminar flow operating environments. In orthopedics, airborne contamination is a primary concern, given the susceptibility of implantables to sepsis. The Northumbria orthopedic team spends vast sums of money on protective laminar flow ventilation systems and personal isolation "space suits" for this very reason. With the primary goals of providing better care to patients and improving patient safety, the Northumbria orthopedic team set out to investigate and eliminate potential sources of infection.

After testing different forms of positioning and draping, they investigated the equipment in their operating room. Forced-air warming equipment, with its disruptive air flow and vast wattage output, was a natural object of concern. Their findings were quite shocking.

This video, produced by the Northumbria orthopedic team, shows the disruptive effect of forced-air equipment on protective laminar flow, using neutral-buoyancy helium bubbles to show air currents. As a control, the team tested conductive fabric warming blankets as well. The video evidence is quite clear: forced-air, in a normal operating room setting, disrupts laminar flow. Conductive fabric warming does not. Prudence, and good sense, dictates that these findings be taken into consideration when choosing between forced-air and conductive fabric warming systems.

The Northumbria orthopedic team has set up their own blog to show their findings. With patient safety in mind, they have compiled excellent research and the visual evidence is stunning. To access their blog, click on the following link: www.northumbriaorthopaedics.blogspot.com

Hot Air Disrupts the Protection of Laminar Flow

Watch the Video about Laminar Flow Disruption by Forced-air Warming



Please watch the video. It is honest, unaltered footage taken in a simulated OR of laminar flow ventilation being disrupted by forced-air warming. What you will see is physics at work.

The physics is simple: heat rises! After passing over the patient’s skin and dropping near the dirty floor, the waste hot air rises--overpowering the ultra- clean downward air current of laminar flow-- and then, having cooled, falls into the surgical site.

Reducing surgical site infections (SSIs) is of the highest priority for hospitals, insurance companies, and national health initiatives. Not to mention patients and their families.

Providing an ultra clean surgical environment with laminar flow has become the standard of care because it helps reduce hospital acquired infections. A study cited by the Centers for Disease Control revealed a reduction in SSIs from 3.4% to 1.6% merely as a result of laminar flow.

Warming surgical patients, of course, is also the standard of care. Normothermic patients are far less likely to acquire a post-operative wound infection—64% less likely by one study (Mahoney, AANA J, 1999)—than those who aren’t warmed. The device used to warm patients, however, should not increase the risk of bacterial contamination.

Fortunately, there is an [air-free] alternative. HotDog® conductive fabric warms as effectively as forced air, but is safe, eco-friendly, and much less expensive.

We encourage you to conduct the simple test detailed at the end of the video to prove that the forced-air exhaust heat rises in your operating room. Of course, it will. Hot air always rises.

We want to hear your comments about hot air and its effects on laminar flow. Your thoughts and knowledge are important to us.