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
The critical relationship between airborne microbiological contamination in an operating theatre and surgical site infection (SSI) is well known. The aim of this annotation is to explain the scientific basis of using settle plates to audit the quality of air, and to provide information about the practicalities of using them for the purposes of clinical audit. The microbiological quality of the air in most guidance is defined by volumetric sampling, but this method is difficult for surgical departments to use on a routine basis. Settle plate sampling, which mimics the mechanism of deposition of airborne microbes onto open wounds and sterile instruments, is a good alternative method of assessing the quality of the air. Current practice is not to sample the air in an operating theatre during surgery, but to rely on testing the engineering systems which deliver the clean air. This is, however, not good practice and microbiological testing should be carried out routinely during operations as part of clinical audit. Cite this article:
Deep infection was identified as a serious complication in the earliest days of total hip arthroplasty. It was identified that airborne contamination in conventional operating theatres was the major contributing factor. As progress was made in improving the engineering of operating theatres, airborne contamination was reduced. Detailed studies were carried out relating airborne contamination to deep infection rates. In a trial conducted by the United Kingdom Medical Research Council (MRC), it was found that the use of ultra-clean air (UCA) operating theatres was associated with a significant reduction in deep infection rates. Deep infection rates were further reduced by the use of a body exhaust system. The MRC trial also included a detailed microbiology study, which confirmed the relationship between airborne contamination and deep infection rates. Recent observational evidence from joint registries has shown that in contemporary practice, infection rates remain a problem, and may be getting worse. Registry observations have also called into question the value of “laminar flow” operating theatres. Observational evidence from joint registries provides very limited evidence on the efficacy of UCA operating theatres. Although there have been some changes in surgical practice in recent years, the conclusions of the MRC trial remain valid, and the use of UCA is essential in preventing deep infection. There is evidence that if UCA operating theatres are not used correctly, they may have poor microbiological performance. Current UCA operating theatres have limitations, and further research is required to update them and improve their microbiological performance in contemporary practice. Cite this article:
