Warm-Air Blowers Disperse Pathogens to Surgical Sites

A new study suggests that heated-air blanket blowers, designed to keep patients at a safe temperature, also interfere with operating room (OR) ventilation systems, exacerbating the dispersion of squames.

Researchers at Oregon State University (OSU; Corvallis, USA), and the University of California Irvine (UCI, USA) conducted high-fidelity, predictive fluid flow simulations of the interactions between the rising thermal plumes from forced air warming blowers and the ultraclean ventilation air in an OR, with the intention of exploring if the complex flow patterns between the two streams of air can impact the dispersion of squames to the surgical site.

They first designed a large-eddy simulation (LES) to accurately capture the spatio-temporal evolution of the flow in three-dimensions, together with the trajectories of squames. The LES took into consideration a realistic OR consisting of an operating table, side tables, surgical lamps, medical staff, and a prone patient. They then ran two case studies--one with the blower off and the other with blower on—in order to calculate the Lagrangian trajectories of three million squames initially placed on the floor surrounding the operating table.

The results show that with the blower off, squames are quickly transported by the ventilation air away from the operating table and towards the exit grilles. In contrast, with the hot air blower turned on, the ventilation airflow is disrupted significantly. The rising thermal plumes from the hot air blower drag the squames above the operating table; they are then advected downwards toward the surgical site by the ventilation air from the ceiling. According to the researchers, the results shed new light on healthcare-associated infection (HAI). The study was published on January 9, 2108, in the International Journal of Numerical Methods in Biomedical Engineering.

“An ultra-clean ventilation system constantly delivers highly filtered air with a uniform downward velocity, and its performance depends on volumetric air flow and proper temperature gradients,” said study co-author Professor Sourabh Apte, PhD, of UCI. “Medical equipment in the OR, and the surgical staff, can disrupt the air flow in ways that increase the amount of bacterial colony-forming units, and so do the rising plumes of hot air from forced-air warming devices that prevent patient hypothermia.”

“This numerical approach is fully three-dimensional and time-dependent, and accounts for the effects of turbulence and heat transfer on the dispersion of squames,” concluded Professor Apte. “The approach is fully predictive and captures the turbulent flow accurately without requiring any tunable parameters. This is the first study of its kind where large-eddy simulation was used to investigate dispersion of squame particles in an operating room.”

Squames are tiny, disc-shaped flakes of skin, about 4 to 20 microns in diameter and 3 to 5 microns in thickness, and with the density of water. Each person sloughs off squames at the rate of about 10 million per day. Squames also host microbial skin colonizers such as Staphylococcus aureus; when the squames and the bacteria that live on them get into surgical sites, surgical site infection (SSI) can be the result.

Related Links:
Oregon State University
University of California Irvine