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:

“The use of forced air warming was found to result in a predicted mean sum of bubble counts equal to 132.5; such a count represents a significant increase in the number of bubbles reaching the surgical site versus both conductive fabric warming and control conditions, which had predicted mean sum of bubble counts equal to 0.48 and 0.01 respectively.”

Convection currents were detected between the anesthesiologist’s body and the anesthesia drape, which mobilized unsterile air from beneath the drape upward and over the top of the anesthesia drape, directly into the surgical site.

No convection currents were detected when conductive fabric warming or no warming was used.

Researchers conclude, “Excess heat from forced air warming resulted in the disruption of ventilation airflows over the surgical site, whereas conductive patient warming devices had no noticeable effect on ventilation airflows. These finding warrant future research into the effects of forced air warming excess heat on clinical outcomes during contamination-sensitive surgery.”

It’s been well established that patient warming is necessary to combat the adverse effects of intraoperative hypothermia. The importance of choosing the correct patient warming method for the type of surgery performed, however, cannot be overstated.

The Belani study is consistent with three other studies published within the past eight months. The results suggest that the safest choice for surgeries involving implanted foreign materials is air-free conductive fabric patient warming.