Recent A & A study: “These findings warrant future research into the effects of forced air warming…during contamination-sensitive surgery.”

August 2013
 
Research in the August edition of Anesthesia & Analgesia, a publication of the International Anesthesia Research Society, and appearing under the name of the Anesthesia Patient Safety Foundation stated:

 “[F]orced air warming was found to establish convection currents that mobilized resident air from nonsterile areas (under the anesthesia drape) upward and into the surgical site.”

The clinical concern, according to the article, is that the convection currents created by Bair Hugger will mobilize contaminants and/or impede the ventilation systems’ ability to clear contaminants from the surgical site.  The concerns, they stated, “are most relevant for smaller airborne particles…such as free-floating bacteria and skin cell fragments.”

The study compared the impact of Bair Hugger warming with air-free HotDog conductive fabric warming.  No convective currents were detected when HotDog warming was applied.  In explanation, the scientists stated:

 “Because conductive blankets (like HotDog) are localized in their application, they tend to have higher thermal efficiencies and contribute less excess heat to the environment than forced air.”

In contrast, Bair Hugger “was found to have a significant disruptive impact on clean airflow patterns over the surgical site….”

Evidence Growing Against Safety of Forced-air Patient Warming

Yet another peer-reviewed study—the third in the past five months—has been published showing that forced-air patient warming generates convection current activity in the vicinity of the surgical site, which could lead to contamination of the sterile field.

The study, published by Dr. Kiran Dasari in the March issue of Anaesthesia, is more evidence that a significant patient safety issue exists.  Surgeries with implanted foreign materials, like hip and knee replacements, could be greatly compromised depending on the type of warming technology used.

Another Study Shows the Risks of Using Forced-air Patient Warming

Researchers in the UK published a study in the February, 2012, issue of the Journal of Bone and Joint Surgery-Br examining the effects of forced-air warming on operating room airflow and surgical site sterility.

Summary:

“Forced-air warming resulted in a significant mean increase in the temperature (1.1°C vs 0.4°C, p<0.0001) and number of particles (1038.2 vs 224.8, p=0.0087) over the surgical site when compared with [HotDog®] warming, which raises concern as bacteria are known to require particles for transport.”
 

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 without forced-air, according to a newly published study.

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.

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.