Nursing Journal: Forced-Air Warmers May Allow Pathogens to Contact Surgical Wounds

October 10, 2013

   

AORN Journal, noting concerns about infection risk from forced-air warmers, called for multi-center, randomized, controlled trials. Evidence of bacteria in the air-flow paths of forced-air warmers; authors ask manufacturers to consider redesign.

In a continuing-education review article in the October issue of AORN Journal, published by the Association of Operating Room Nurses, the authors examined 192 sources.  Their conclusions included the following:

• “Clinicians should take steps to prevent health care–associated infections from the use of forced-air warmers….”  Such steps include “routinely and meticulously” cleaning the devices.

•  Forced-air warmers may interrupt the flow of filtered air toward the area of the wound and may allow dust particles containing pathogenic organisms to come into contact with the wound.

•  Five separate studies suggested that forced-air warmers could be harboring bacteria or bacteria-containing particles.

Among the research considered by the authors was “Forced-air warming and ultra-clean ventilation do not mix: an investigation of theatre ventilation, patient warming and joint replacement infection in orthopaedics,” by UK orthopedic surgeon PD McGovern et al and published in the Journal of Bone & Joint Surgery.  The research included 1,437 patients undergoing hip or knee replacement.  The “Finding and comments” of the AORN Journal authors included:

“High risk of developing deep infections for subjects warmed with forced-air warming systems (odds ratio, 3.8; P=.024).”

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….”

Infection Guidance: Air Turbulence in Operating Room Increases Risk of Orthopedic Infection

In its Guide to the Elimination of Orthopedic Surgical Site Infections, the Association of Professionals in Infection Control and Epidemiology (APIC) states, “If airflow is interrupted, rapid air turbulence can stir settled particles, enabling them to become airborne thus increasing the risk for wound contamination.” By applying recent research to APIC’s Guidance, StopSurgicalInfections.org found that forced-air warming systems violate APIC’s Guidance “by drawing potentially contaminated particles from below the operating table into the surgical site.”   

Minneapolis, MN July 25, 2013

According to the Association of Professionals in Infection Control (APIC), the maintenance of uninterrupted, downward airflow during orthopedic surgery is “vitally important.” Several recent articles published in top peer-reviewed medical journals, however, confirm that forced-air patient warming, such as 3M’s Bair Hugger, produces rising, turbulent convection currents that can mobilize floor-level contaminants.

The printing and distribution of APIC’s Guide was sponsored by 3M.  APIC, of course, neither endorses nor is affiliated with this press release.

“The APIC guidance,” says Dr. Scott Augustine, inventor of Bair Hugger, “ summarizes the reason that researchers have questioned the safety of forced-air patient warming (“FAW”) in orthopedic implant and other ultra-clean surgeries.  I believe the research is conclusive—the largest study involved a retrospective analysis of 1,437 hip or knee replacements. It showed a 74.6% decrease in deep joint infection when FAW was discontinued and replaced with air-free warming.”

New ECRI Guidance Expresses “Concern” About Forced-Air Warming in Implant Surgery

In the latest issue of Health Devices, ECRI Institute analyzed the safety of forced-air patient warming, concluding that thermal currents are “particularly worrisome” in implant surgery. Dr. Scott Augustine, inventor of both Bair Hugger and (air-free) HotDog patient warming and CEO of Augustine Temperature Management, comments.

Minneapolis, MN (PRWeb), April 17, 2013 -  After reviewing multiple published, peer-review articles addressing the consequences of the convection currents created by the waste heat produced by forced-air devices, ECRI stated:

• “The disruption of air-flow patterns is particularly worrisome in laminar-flow and ultraclean ORs, in which a wide variety of implant surgeries are performed.”
• “This is especially concerning during orthopedic surgeries because contamination of the surgical site may present a greater risk of developing a PJI, which is harder to treat and resolve than would be the case with SSIs in general.”

The Paradox of Forced-Air Patient Warming

Studies show that forced-air warming (FAW) reduces soft-tissue surgical infections. How can FAW be linked to increased deep-joint infections?

The paradox is easy to explain: BIOFILM.  A bacterium that lands on a prosthetic implant can secrete a coating of biofilm that protects it from both antibodies and antibiotics. Bacteria in soft-tissue cannot form effective biofilm coatings.

Secretion of biofilm allows a single airborne germ to cause a deep infection of a joint implant (Lidwell, 1983).  When the germ lands on the new implant, it protects itself in a biofilm coating and then sprouts weeks-to-months later as a catastrophic deep joint infection.  The increased airborne contamination from FAW vastly increases the chances of an airborne bacterium landing on the new implant.

In contrast, without biofilm protection, the germs in soft-tissue are susceptible to antibiotics and to an immune system activated by heat.  As a result, the creation of soft-tissue surgical infections require large inoculums of more than 100,000 germs (Elek & Cohen, 1957).

This also explains why soft-tissue surgical infections may not be increased by contaminated FAW air, while blowing even one germ into the surgical site during implant surgery can have significant negative concequences.

Watch this terrific video about bacterial biofilms 

produced by the Arthroplasty Patient Foundation:

Here is another interesting video about bacterial biofilms 

and orthopedic implants produced by the Arthroplasty Patient Foundation:

Evidence of the risks of forced-air warming just keeps growing.

A study published online ahead of print in Anesthesia & Analgesia concludes that forced-air patient warming produces waste heat that disrupts operating room ventilation airflows over the surgical site, transporting non-sterile air to the area and hindering the ventilation system’s ability to clear potential airborne contaminants.

“There are some in our industry that would like you to believe that hot air doesn’t rise,” says Dr. Scott Augustine, “this study proves, once again, that that argument is insulting to science and common sense.”

Belani, et al, focused on contamination-sensitive surgery at the University of Minnesota, using a mannequin draped for total knee replacement.  Introducing neutral buoyancy bubbles near the mannequin’s head, researchers found a significant increase in bubble-count over the surgical site when forced air warming was used, as opposed to conductive fabric or the control.  The study states:

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.

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.

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.