Surgical Sterility at Veterinary Hospitals is Assured by Astell Equipment

The Phillip Leverhulme University of Liverpool Equine Hospital treats over 2,000 equine patients each year specialising in gastroenterology, oncology, ophthalmology, orthopaedics and respiratory problems.

As a surgical hospital, the standards of sterility are as high as in any hospital for humans. Instruments and dressings used in operations are all sterilised, as are contaminated surgical wastes prior to disposal. Autoclaving is the proven method so, when they needed a new autoclave, they bought an Astell 216 litre capacity Logicolor Square Section Sterilizer.

Sterility means the statistically complete destruction of all micro-organisms including the most resistant bacteria and spores. This is a condition that is difficult to achieve and harder to prove, but Astell's sterilizers are designed to do just that. To achieve a temperature of 121°C or more, steam has to be pressurised to at least 1barg, and that means that the autoclave which contains it is classified as a pressure vessel. Astell's pressure vessels are all constructed in 316 stainless steel and are all fully compliant with PD5500/PED/97/23EC.

Operator safety is paramount in autoclaves and HSE PM73 requires that the door is interlocked. The Square Section Sterilizer has an interlocked sliding door which inhibits the sterilisation cycle until the door is closed and locked and prevents the autoclave being opened if the internal temperature or pressure is above a preset value. Further, the door is thermally insulated to prevent the surface temperature presenting a hazard to operators and the sterilising cycle cannot start until the door is closed and locked.

The Advanced Water Cooling, available as an option on most Astell units, uses mains water, circulated through cooling coils in contact with the stainless steel chamber, to give a rapid decrease in temperature when the sterilisation cycle is complete. This means a substantial reduction in cycle time, and is why a single sterilizer can meet all the Equine Hospital's needs.

When an autoclave is first loaded, it is full of air which normally has to be displaced by the steam. Astell include a vacuum system evacuates the vessel at the start of the cycle to remove that without losing expensive steam. As the vessel cools down at the end of the cycle any steam remaining inside it condenses, which means that the sterilised load could be left wet. This can lead to recontamination, and is a particular problem with dressings. Whilst this can be avoided by adding a separate drying stage prior to storage, again the vacuum system can be used to advantage. By evacuating the vessel under vacuum on completion of the sterilisation cycle, the residual steam is almost completely eliminated, leaving the load dry.

With an eye to sustainability, water conservation is becoming more and more important. The autoclave incorporates an internal reservoir tank which is connected to a mains cold water supply. The water inlet is controlled by level switching and includes an air gap to comply with water regulations. Once filled, the reservoir provides sufficient water for up to 20 cycles and also acts as a collection vessel for both condensate and water which is returned from the autoclave chamber at the end of the cycle. A thermostat only allows mains water to be added to the reservoir if the water temperature rises above a set point, which minimises the amount of water going down the drain and greatly reduces the water consumption by comparison with continuous feed autoclaves. Just in case anything goes wrong, the system pumps are protected from running dry by a float switch mounted in the reservoir. This overrides the water conservation system and feeds the water to the water tank regardless of the water temperature.

It is absolutely essential that sterilisation temperature is reached in all parts of the autoclave, and this is controlled by Astell's new LogiColor control system. Based on an industrial PLC controller with analogue and digital input/output modules, this state of the art controller distils Astell's 80 years of experience in a user friendly system that meets the expectations of even the most demanding of Sterile Services Units.

Control is by the unique Astell SECURE+ micro-computer, a user friendly, fully automatic controller that ensures repeatable, safe and accurate sterilisation time after time. The control system is based on an industrial PLC controller combined with a number of analogue and digital input and output units. The operator interface has a large LCD display which gives an easy to read stage by stage report on cycle time, temperature and pressure.

The controller has eight sterilisation programmes which are factory set before delivery, but can be easily changed by the operator using the multiple access level, PIN protected membrane touch pad. This allows the operator to set up pre-programmed cycles for example, 121°C for 15 minutes for wrapped instruments, 134°C - 121°C for 15 minutes for unwrapped instruments and 134°C for 3 minutes for Bowie Dick testing and so on. Setting the programmes is interactive using simple question and answer functionality. Among the user selectable options are delayed start, allowing sterilisation to take place overnight; sterilisation time and temperature; Holdwarm capability to maintain the autoclave at a pre-set temperature after sterilisation until required and the cooling lock release temperature.

An RS232 port provides an output to a PC or printer for cycle validation, but an optional integral Data Printer is also available. Built into the controller pod, this printer provides a permanent and traceable record of time, temperature, pressure, batch number, sterilisation cycle name and operator signature. The printer also provides reports of cycle settings and servicing information.

Software is written in Automation Basic for maximum clarity and is split into well-defined blocks, each of which performs a specific function. The program is stored on a Flash Card and the controller has a battery backed 64MB memory. An RS232 interface allows connection to a wide range of peripheral devices such as printers, data loggers and building management systems so that the temperature right through the sterilisation cycle and this can be recorded in accordance with Good Laboratory Practice.

Although the Equine Hospital has a high profile it's the University of Liverpool's new £9.6million Small Animal Teaching Hospital that is currently getting more attention. Opened in April 2007, it is the most modern and well-equipped hospital for small animals in the UK. The hospital covers 2500m2 and has space for 72 in-patients at any one time. With exemplary foresight, the designers have provided separate waiting areas for cats and dogs.

The new facility has a range of state of the art diagnostics such as CT and MRI scanning and is equipped with a Varian Clinac 2100 linear accelerator making it the only veterinary radiotherapy facility north of Cambridge. In terms of surgical treatment, the new hospital has an extremely modern operating suite with four operating theatres supported by an anaesthetic induction suite and an intensive care unit. All the theatres are designed with positive pressure ventilation with filtered air to ensure extremely high levels of asepsis. This is a major factor in prevention of infection, particularly for more complex operations such as joint replacements. Sterilisation of instruments, dressings and waste materials is provided by a 150 litre Astell Swiftlock benchtop autoclave, a smaller unit that still supports most of the features of its larger Square Section stable-mate.

So surgical sterility at both of the University of Liverpool's animal hospitals is assured by equipment that has been developed over half a century. But these days equipment not only has to work, it has to be seen to work so, as part of the commissioning programme, Astell will validate the autoclaves, by multi-point temperature mapping, to establish suitable loading configurations and cycle parameters which will assure repeatability of performance. Astell's UKAS accreditation means that the validation documentation is fully traceable and is a guarantee of quality. And that's straight from the horse's mouth!

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Source : Astell View Company Information

Posted on September 20, 2007