The documentation of deep infection rates in joint replacement is fraught with multiple difficulties. Deep infections acquired in theatre may present late, but some later presenting deep infections are clearly haematogenous, and not related to surgical management. The effect of Ultra Clean Air on infection rates was published by Charnley in 1972 (CORR,87:167–187). The data is valuable because large numbers of THRs were performed in standard and Ultra Clean theatres, and detailed microbiology of the air was also recorded. No IV antibiotics were used, so only the effect of air quality was studied.

We extracted the data on theatre type and numbers from Table 3, and numbers and intervals from surgery of deep infections from Table 7. Theatre types with 300 air changes per hour and 3.5 CFU/M³ were classified as Ultra Clean. A logistic regression model was used to examine the effect of theatre type and time elapsed after procedure on the probability of becoming infected.

The model suggests that, controlling for time period, Ultra Clean Air is associated with a significantly lower probability of infection, with an OR of 0.30, p = 2.74 × 10⁻⁶. The effect is larger earlier post-surgery, but it does persist. The results are best reviewed as a graphic, which shows that Ultra Clean Air clearly affects the deep infection rate for up to four years post-surgery.

Ultra Clean Air reduces infection rates for up to four years post-surgery, so it is safe to assume that infections presenting after this are haematogenous. Ultra Clean Air does not eliminate early deep infection, so some early infections are not related to air quality. It is not practical to undertake widespread detailed retrospective analyses of cases. When monitoring infection rates there needs to be a balance between failing to record infections related to surgical technique and waiting many years to record low numbers of very late presenting problems. We suggest that registries should regard infections documented within three years of surgery as treatment complications.

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Introduction

Operating theatre airflow can be measured using pulsed lasers (particle image velocimetry) but the process is difficult to do in 3D. Cup, vane or hot wire anemometers provide only 2D information. 3D measurements enable better understanding of airflow.

As a result of laser imaging studies in an ultraclean theatre we concluded that obstructions to horizontal airflow at the periphery might produce areas of high particulate residence times. High residence times may allow a higher proportion of infected particles to land. We decided to investigate this effect by placing settle plates in defined positions on instrument trays during surgery.

In an initial study contamination was 0.25 colonies/plate/hour. When the surgeon, assistant and scrub person all used a body exhaust system the contamination rate was 0.04 colonies/plate/hour. We then organised the instrument tables with two large tables orientated so that the scrub person did not have to stand between the airflow and the table. We placed plates on both trays with the locations recorded.

With the instrument trolleys in optimised positions the contamination rate remained consistently at 0.04 colonies/plate/hour. An animation was produced showing how the bacterial colonies appeared over 18 hours of surgery. The majority of the contamination occurred on the surgeons’ side trolley at the opposite end of the trolley to the surgeon.

Ultraclean enclosures in the UK are specified by HTM03-01, which sets a standard of <10 cfu/cubic meter measured by active air sampling. The measurement does not however take place during surgery, as it is very difficult to perform air sampling during surgery. There is a reasonable correlation between air contamination and settle plates so they are a viable method for during surgery monitoring.

In a modern operating enclosure, using body exhausts, our contamination rate compares favourably to the fourth phase of Charnley's classic study in which he used 300 air changes/hour in the prototype closure. The rate compares favourably to the multi-centre Italian GISIO-ISChIA study. The contamination rate achieved could form a basis for comparative audits based on realistic during surgery monitoring.

Introduction

Deep prosthetic joint infection is a major cause of morbidity. Previous work has shown that infected skin scales shed by members of staff in the operating theatre are the key source of infection. Much attention has been given to the design of ultra clean operating theatres but remarkably little attention has been given to factors controlling skin scale shedding.

The aim of this study was to develop a novel method of direct visualisation and quantification of skin scales and to assess the effect of a simple skin care regimen on skin scales.