Forced-air patient warming blankets disrupt unidirectional airflow

Area of Science:

• Surgical Safety
• Biomedical Engineering
• Infection Control

Background:

• Forced-air warming blankets generate waste heat, previously linked to increased airborne particles over surgical sites.
• The precise mechanism and origin of these particles remained unclear, necessitating further investigation.

Purpose of the Study:

• To visualize airflow dynamics in an operating theatre during a simulated total knee replacement.
• To elucidate the mechanism by which forced-air warming blankets increase airborne particle concentration at the surgical site.

Main Methods:

• Utilized neutral-buoyancy helium bubbles to visualize airflow over a simulated total knee replacement.
• Employed a smoke machine below the operating table to generate particles, simulating potential contamination sources.
• Maintained the same theatre setup, warming devices, and controls as a previous study for consistency.

Main Results:

• Waste heat from forced-air warming blankets elevated surgical drape air temperature by over 5°C.
• This temperature increase generated convection currents that opposed the unidirectional airflow, causing turbulence.
• Particle concentration increased 1000-fold (2,174,000 particles/m³) compared to radiant warming (1000 particles/m³) and control (2000 particles/m³).
• These currents drew contaminated particles from beneath the operating table into the surgical field.

Conclusions:

• Forced-air warming blankets create significant airflow disturbances and turbulence in the operating theatre.
• The study identified a clear mechanism for particle contamination originating from below the surgical site, driven by the warming device's heat.
• Findings highlight a potential risk of increased surgical site contamination associated with forced-air warming systems.