ANSWERS

1. What is meant by "aseptic technique"?
   All the steps taken to prevent contact with micro-organisms.
2. What is the term used to describe the presence of pathogens or their toxic products in the blood or tissues of the patient?
   Sepsis (commonly known as infection).
3. In what part of the body would septicaemia be found?
   The blood stream.
4. Why might advanced periodontal disease predispose a patient to renal and cardiac problems?
   Bacteria have a direct route to the blood stream via oral cavities and lesions, and as you know, the oral cavity is seething with bacteria. These bacteria then migrate to other areas of the body where they reproduce further and cause damage to cells, tissues and organs.
5. Describe the difference between asepsis and sterilisation.
   Asepsis means the complete exclusion of all micro-organisms and spores, whilst antisepsis describes the prevention of sepsis (infection) by the destruction or inhibition of micro-organisms using an agent that is safe and effective upon living tissue.
6. What is the difference between disinfection and sterilisation?
   Disinfection is the removal of micro-organisms but not necessarily spores; sterilisation is the destruction of ALL micro-organisms and spores.
7. When do most surgical wound infections occur and why?
   Intra-operatively (ie. at the time of surgery) as a result of poor aseptic technique.
8. What is the difference between endogenous and exogenous micro-organisms?
   Endogenous micro-organisms originate from within the body of the patient, whilst exogenous micro-organisms originate from the exterior of the body and may include contaminates from the skin and coat aswell as environment sources of micro-organisms such as the air and instruments or equipment.
9. List 4 factors that influence wound infection.
   • Virulence (potency) of the bacteria involved.
   • Surgical trauma and damage to the vascular supply.
   • Impaired immune response which will lower the resistance of the patient.
   • Contamination of the wound.
10. Differentiate between a clean-contaminated and a contaminated wound.
    A clean contaminated wound is a surgical wound made under aseptic conditions but penetrating the oro-pharynx, respiratory, alimentary or uro-genital tracts but without undue contamination or spillage. A contaminated wound is a fresh traumatic wound of less than 6 hours duration or a major break in aseptic technique. Also surgery that encounters inflamation.
11. Give an example of a clean-contaminated wound.
    End to end anastomosis.
12. What are the 2 main types of sterilisation?
    • Cold sterilisation.
    • Heat sterilisation.
13. List 4 types of cold sterilisation.
    • Ethylene oxide.
    • Chemical solutions such as Novasapa.
    • Gamma irradiation.
14. List 4 disadvantages of sterilisation by ethylene oxide.
    • Toxicity.
    • Irritant to tissue.
    • Extremely inflammable.
    • Time consuming.
15. How does ethylene oxide work?
    It inactivates the DNA of viruses, bacterial cells and spores and fungi, thus rendering them incapable of reproduction.
16. A pack of instruments is put into the ethylene oxide steriliser at 7pm on Monday. At what time and day would this pack be safe to use?
    The pack would be ready at 9pm on Wednesday (after 36 hours; comprising of a 12hour sterilisation period, a 2 hour aeration period where the container/cupboard remains shut, plus 24 hours ventilation after removal from the steriliser).
17. At what temperature is ethylene oxide sterilisation performed?
    20°C.
18. What is the main advantage of ethylene oxide sterilisation?
    It is ideal for items that are destroyed by heat such as fibre-optic equipment, plastic items such as catheters, rubber items such as endotracheal tubes, delicate optical instruments, high-speed drills and burrs and battery operated drills.
19. What material should not be sterilised by ethylene oxide and why?
    Polyvinylchloride (PVC) since it may react with the gas.
20. What colour are the stripes on ethylene oxide sterilisation indicator tape before and after exposure to the gas?
    Yellow prior to exposure, and red after exposure.
21. What limitation is a concern when using ethylene oxide indicator tape?
    The colour change takes place very soon after exposure to the gas, so there is no evidence that the correct duration of exposure was undertaken.
22. State 2 alternatives to ethylene oxide indicator tape.
    • Chemical indicator strips (these change colour after the correct exposure period).
    • Spore strips.
23. What is the main disadvantage of spore strips?
    They do not provide an immediate indication of sterility since they must be incubated for 72 hours following the completion of the sterilisation cycle.
24. Why are formaldehyde and glutaraldehyde no longer in common use?
    The fumes are extremely dangerous. COSSH regulations limit the use of both substances.
25. List 6 factors to be taken into consideration when using chemical solutions for sterilisation.
    • Sterilisation may not be guaranteed.
    • Care must be taken to use according to the manufacturers' instructions.
    • Do not use on equipment that may be damaged by moisture.
    • A lid must be placed over the sterilisation container to prevent evaporation and air-borne contaminants.
    • Items should be rinsed well in sterile water prior to use.
    • A fresh solution should be used for each batch of sterilising.
26. How do alcohol-based sterilisation solutions work?
    By the denaturation and coagulation of proteins.
27. Why is sterilisation by gamma irradiation not undertaken in veterinary practices?
    This is an extremely expensive, specialised and highly controlled method of sterilisation. It can only be carried out under strict controlled conditions within industry. You may find some pre-packed sterile items designed for individual use are sterilised by gamma irradiation such as suture materials and needles, dog and cat catheters and irrigation cannulae.
28. State the 2 main types of heat sterilisation.
    • Dry heat (ovens).
    • Steam under pressure (autoclaves).
29. List the 3 types of sterilisation oven and briefly describe each.
    • Hot-air oven - a small, but economical method now largely superseded by the autoclave.
    • High vacuum-assisted oven - a fully automatic and rapid method, but not commonly seen in veterinary practice.
    • Convection oven - these incorporate an air circulation device to achieve a uniform temperature, but are not commonly seen in veterinary practice.
30. Why must dry heat sterilisation be carried out at a higher temperature than moist heat sterilisation?
    Micro-organisms are much more resistant to dry heat and therefore require temperatures of 150-180°C to guarantee sterilisation.
31. State the time and temperature recommended for the sterilisation of non-cutting instruments using a hot air oven.
    160°C for 120 minutes.
32. State the 3 main types of autoclave and briefly describe each.
    • Vertical pressure cooker - A simple machine which operates by boiling water in a closed container with an air vent at the top; this is closed once the air has been evacuated and pressure of 15 psi is allowed to build up.
    • Horizontal/vertical downward displacement autoclave - An automatic, electrically operated boiler is employed as a source of steam. Air is driven out of the vent at the top effectively by downward displacement.
    • Vacuum assisted autoclave - This efficient and fully automatic autoclave uses a vacuum pump to rapidly evacuate air from the chamber at the beginning of the cycle enabling steam penetration. A second vacuum withdraws moisture after sterilisation and dries the load.
33. Which type of autoclave is also known as a porous load autoclave?
    The vacuum assisted autoclave.
34. If an autoclave were operating at 126°C at a pressure of 20 psi, what sterilising time would be necessary to ensure the destruction of micro-organisms?
    10 Minutes.
35. List 5 factors to be taken into account when using an autoclave.
    • Ensure that the autoclave is not overloaded (there must be adequate space to allow the steam to circulate freely).
    • Ensure that the inlet and exhaust valves are not obstructed.
    • Effective penetration of steam is reliant upon the absence of grease and protein material.
    • Servicing should be carried out twice yearly (or every 3 months in the case of vacuum assisted autoclaves with a separate boiler).
    • Thermocouple testing is recommended at least annually. Thermocouples are electrical leads with temperature sensitive tips that can record the temperature throughout a cycle via a recording device outside of the autoclave.
36. State the 4 main methods of monitoring autoclave sterilisation efficiency and briefly describe each.
    • Bowie Dick tape - beige tape with chemical stripes that turn dark brown when a temperature of 121°C is reached.
    • Chemical indicator strips - these show a colour change (from yellow to purple) only when the correct temperature, pressure and time have been reached; different strips are available for different cycles.
    • Browne's tubes - small glass tubes filled with an orange-brown liquid that turns green when a certain temperature has been maintained for a required period of time; different tubes are available for different cycles and also for hot air ovens.
    • Spore test strips - these are impregnated with bacteria and are incubated for 72 hours after the cycle; a successful sterilisation process will obviously show no growth.
37. State 2 disadvantages of Bowie Dick tape.
    • It does not provide evidence that the required temperature was maintained for the correct duration.
    • It is designed for sterilising at 121°C (not 126 or 134°C).
38. Of the 3 methods listed in Q36, which is the most effective and why?
    Chemical indicator strips, since they are the only method which shows that all 3 parameters are met (ie. temperature, pressure and time) and give immediate results once the sterilisation cycle is complete.
39. List 6 materials/containers used for the packing of supplies for sterilisation.
    • Nylon film.
    • Seal & peel pouches (made of paper and plastic).
    • Paper.
    • Linen sheets.
    • Metal drums.
    • Cardboard boxes/cartons.
40. How should sterile packs be stored?
    • In a dry, dust free environment with good ventilation (ideally within a closed cupboard).
    • Labelled with the date of sterilisation and the initials of the nurse who did the sterilising.
    • Packed loosely on shelves and handled as little as possible to minimise the risk of damage to the bags.
    • Checked regularly for perforation of the packaging and the date of sterilisation (unused packs should be resterilised every 6-8 weeks).