We have recently shown that waste heat from forced-air
warming blankets can increase the temperature and concentration
of airborne particles over the surgical site. The mechanism for
the increased concentration of particles and their site of origin
remained unclear. We therefore attempted to visualise the airflow
in theatre over a simulated total knee replacement using neutral-buoyancy
helium bubbles. Particles were created using a Rocket PS23 smoke
machine positioned below the operating table, a potential area of
contamination. The same theatre set-up, warming devices and controls
were used as in our previous study. This demonstrated that waste
heat from the poorly insulated forced-air warming blanket increased
the air temperature on the surgical side of the drape by >
5°C.
This created convection currents that rose against the downward
unidirectional airflow, causing turbulence over the patient. The
convection currents increased the particle concentration 1000-fold
(2 174 000 particles/m3 for forced-air warming Cite this article:
Patient warming significantly decreases the risk
of surgical site infection. Recently there have been concerns that forced
air warming may interfere with unidirectional airflow, potentially
posing an increased risk of infection. Our null hypothesis was that
forced air and radiant warming devices do not increase the temperature
and the number of particles over the surgical site when compared
with no warming device. A forced air warming device was compared with
a radiant warming device and no warming device as a control. The
temperature and number of particles were measured over the surgical
site. The theatre was prepared as for a routine lower-limb arthroplasty
operation, and the same volunteer was used throughout the study. Forced air warming resulted in a significant mean increase in
the temperature (1.1°C
