Aseptic Technique in Rodent Surgery



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Introduction


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Key Points

  • Prepare a protocol and a list of equipment that will be required before you start any surgical procedure.
  • Make sure all the required facilities and equipment have been booked.
  • Ensure an assistant is available.
  • Make sure equipment is prepared for use.
  • When using heat pads, monitor the temperature of both the animal and the heat pad, to ensure correct operation.


Instruments


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Key Points

  • Instruments must be sterilised before they are used for aseptic surgery.
  • Ideally, a separate set of sterilised instruments should be used for each animal.
  • For batch surgery for rodents, an acceptable compromise is to sterilise the instrument tips using a hot bead steriliser.
  • Instruments first need to be cleaned using a sterile brush, in sterile water, to avoid becoming clogged with organic material.
  • Sterile water must be used, not saline for cleaning instruments before use of a hot-bead steriliser.
  • Some brands of toothbrush can be autoclaved successfully, and included in the instrument pack.
  • The instrument tips are briefly placed into the hot-bead steriliser, according to the manufacturer’s instructions.
  • Replace them on a sterile drape, ready for use on the next animal.
  • Briefly immersing instruments in alcohol is NOT an effective means of sterilisation.


Other Materials


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Key Points

  • All other materials needed for the surgical procedure that will come into contact with the surgical site must be sterile and must be used within their stated expiry dates.
  • It is often convenient to purchase items such as scalpel blades and sutures in sterile packs, which are opened when required.
  • Delicate materials, for example catheters, that could not withstand autoclaving can be purchased pre-sterilised, or sterilised using other methods, such as ethylene oxide.


Preparation of the Animal



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Key Points

  • Clip the fur from the surgical site after the animal has been anaesthetised.
  • Remove the clipped fur with a vacuum cleaner.
  • Perform this initial clipping in a separate area so that the operating area is not contaminated.
  • When clipping mice, particular care needs to be taken to avoid damaging the delicate skin.
  • Clean the skin using a suitable disinfectant, for example Chlorhexidine, either in alcohol or water – but avoid using too much disinfectant solution, as this can increase the risk of the animal becoming hypothermic.
  • Alcohol alone is not suitable for disinfection of the skin.
  • In both rats and mice, ointment should be applied to the eyes to prevent drying during anaesthesia.


Preparation of the Surgeon


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Key Points

  • The surgeon should wear appropriate protective clothing to avoid contaminating the surgical site.
  • Wearing a head cover and mask is strongly recommended, but the most important step is for the surgeon to perform effective disinfection of their hands, by “scrubbing up” and then putting on a sterile gown and sterile surgical gloves.
  • The process of hand-washing aims to remove surface dirt and grease from your skin, and allow sufficient contact time with the disinfectant soap to kill or inhibit bacteria in the outer layer of the skin.
  • The only time a scrubbing brush should be used is to clean under your nails, the remainder of the process is just careful and repeated hand-washing.
  • Total contact time varies with the disinfectant used – 5 minutes is recommended for Chlorhexidine and Povidone.


Preparation for Surgery


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Key Points

  • An assistant should open the outer wrapping of instrument packs, sutures, and scalpel blades.
  • The surgeon needs to take care when unwrapping the pack to drop the corners of the drapes so that the back of their hand does not touch the surface of the table.
  • The surgeon drapes the animal, once again taking care not to touch any non-sterile surface.
  • Using a drape prevents sterilised items touching the animals’ fur, and becoming contaminated.
  • When using a paper drape, a suitably-sized hole can be cut to access the surgical site. Avoid cutting along one of the pre-folded sections as this can prevent the drape conforming to the animal.
  • The sterile field can be extended by using an additional paper or cloth drape.
  • Drapes may need to be cut to size, or positioned carefully so that the position of the animal’s nose in the face mask can be monitored – alternatively a transparent drape can be used.
  • Several mask designs (such as the one used to anaesthetise the mouse) provide much more secure placement of the animal’s nose.
  • The position of the head can be fixed using tape, but care must be taken not to interfere with respiratory movements, or to fix the animal’s limbs in an abnormal position.


The Surgical Procedure


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Key Points

  • Check that all the instruments needed are present and arranged in a convenient order before undertaking surgery.
  • After use, each instrument should be placed back on a sterile drape.
  • Maintaining aseptic technique is much easier, and procedures will be completed more rapidly when using an assistant.
  • If an assistant is not available throughout the procedure, non-sterile surfaces that may need to be handled (for example an anaesthetic vaporiser) can be covered with a sterile wrapping, or touched using a large sterile swab which is then discarded.


Batch Surgery


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Key Points

  • Aseptic techniques can be maintained throughout a series of procedures but use of an assistant becomes almost essential.
  • After completing the first procedure, the surgeon lifts and disposes of the sterile drape.
  • The assistant then moves the animal to a recovery area, or directly into a warm incubator.
  • The next animal to undergo surgery is then anaesthetised, clipped, positioned on the table and a skin preparation undertaken by the assistant.
  • Ideally the surgeon will use a new set of instruments, but it is acceptable to use a hot bead steriliser to re-sterilise the tips of the instruments.
  • If a new set of instruments is to be used, the surgeon should re-glove before handling them.
  • This can be done without the need to re-gown.
  • The surgeon re-drapes the animal using a new sterile drape and carries out surgery.

ASEPTIC TECHNIQUE
IN RODENT SURGERY

A comprehensive guide to help research workers apply best practice in aseptic surgical techniques in laboratory rodents.

The material was developed by Newcastle University with the support of the NC3Rs.

National Centre for the Replacement, Refinement and Reduction of Animals in Research. Newcastle University

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