Orthopaedic surgery
microbial carrying particles (MCP) or colony- forming units (CFU) per square metre per hour, or commonly expressed as colonies/90mm plate/hour. There are several advantages to using settle
plates in theatres: l Skilled personnel are not required l Small and portable l Simple to measure MCP settling on instrument trolleys
l Simple to measure MCP settling close to the wound
Despite their advantages, one downside of using settle plates is that they are generally packaged in ways that are not conducive to surgical settings. They typically require sterile scissors to open, posing contamination risks, and making them less convenient to use routinely.
Testing use in UCA theatres: A pilot study Orthopaedic surgeon Andrew Thomas from The Royal Orthopaedic Hospital, Birmingham, led a pilot study to evaluate the feasibility of monitoring ultra clean air (UCA) theatres used for joint replacement surgery, and hybrid facilities used for orthopaedics and vascular surgery, using settle plates instead of traditional volumetric samplers. The study highlighted the ease of using settle
plate counting over traditional slit samplers and also noted that the correlation between volumetric counts and surface counts is already reasonably well established. Audit standards for UCA theatres are set by the Healthcare Infection
Fig 3. Peel apart pack of settle plates designed to simplify sterile deployment Society (HIS) in the UK,10 für Normung (DIN) in Germany11
the Deutsches Institut and the Svenska
institutet för standarder in Sweden (SIS).12 In conventional turbulently ventilated
theatres, HIS guidelines allow a maximum volumetric count of 180 CFU/m3 to 11.2 colonies/90mm plate/hour,10
, corresponding while
the DIN 1946 class 1b standard specifies 6.3 colonies/90mm plate/hour.11 For UCA theatres, HIS guidelines specify a maximum volumetric count of 10 CFU/m3 corresponding to 1.7 colonies/90mm plate/
,
hour, with an optimal standard of 1.0 CFU/m3 corresponding to 0.4 colonies/90mm plate/ hour.10,13
colonies/90mm plate/hour11
The DIN class 1a standard is set at 1.3 and the Swedish
SIS-TS 39 standard at 1.1 colonies/90mm plate/ hour.12
Nevertheless, these standards are not
particularly challenging, as Charnley achieved a remarkable standard of 0.2 colonies/90mm plate/hour in his 1972 study.7 In support of the study investigating the
relationship between microbiological quality of operating theatre air and infection rate, Cherwell, as cleanroom microbiology solutions specialists, collaborated with Andrew Thomas to develop a new peel apart pack settle plate product. These overcame the aforementioned packaging issues and simplified deployment by removing the need for scissors to open them.14 During the pilot study, peel apart packs of
10 plates were aseptically distributed in the theatres, mostly on the instrument trolleys, with two plates placed next to the wound in a total hip replacement, or on the lower abdomen in a total knee replacement procedure. The pilot study in UCA theatres developed a successful monitoring method and found it was possible across multiple theatres to easily meet and exceed the DIN 1a quality standard in routine practice.14
The study concluded that
the HIS recommendation of a maximum of 1.7 colonies/90mm plate/hour was inadequate and should be lowered to encourage a higher air quality to be maintained. One significant result of the pilot study
Fig 2. Two settle plates exposed on an instrument trolley during a total knee replacement 60
www.clinicalservicesjournal.com I October 2024
was that some theatres exceeded the DIN Class 1a standard by a factor of 10. Achieving a
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