How do I… maintain a sterile surgical field – in the field?


Neutering is a life-changing procedure for many stray cats and dogs – indeed sometimes it can be a life-saving procedure by taking the place of former lethal methods of control for groups of stray animals. But neutering is also an elective procedure – one not to done to fix an injury or cure an illness, and one where the animal should leave the procedure as healthy as when it began. It should not be a life-ending procedure.

The key to a successful procedure is the maintenance of an aseptic field and the use of sterile equipment. Often unnecessary compromises are made which result in standards being lowered. A sterile field is possible in all sorts of conditions.

Stray animals and those from loose ownership situations do not require less meticulous surgery – their care needs to be as good as, if not better than, their more cared-for co-species, as they receive less postoperative monitoring; and also because recapture to deal with problems may not be possible.

Working with stray animals, or in field conditions, or the developing world, is not an excuse for poor surgery – which could easily be avoided with forethought. International Cat Care firmly believes that where volunteer vets are used from one country to provide support for a project in a less developed country, it is the responsibility of the organisation sending them to ensure they can operate to the highest standards achievable. There is also a duty on the part of the volunteer, to research the facilities in advance before their project and be willing and able to carry supplies with them.

Stray animals should never be forced to endure poor standards of care where this is avoidable, simply because someone didn’t give adequate thought. It is also unethical to use the ‘rough and ready’ approach to field conditions – ‘surgery under a tree’ – as a fundraising tool – something that International Cat Care will always avoid doing.

Implications of lack of sterility

  • Poor survival of the animals neutered, leading to public mistrust of neutering
  • Wound complications, leading to public mistrust, and costs to put right
  • Reputational damage from local vets, leading to future attempts to bar volunteers
  • Pain and discomfort to animals
  • Overuse of antibiotics to compensate, leading to resistance developing

Disappearance of stray animals postoperatively, leading to surgeons assuming all is okay because they have not seen the consequences of their poor work.

Clipping & prepping

A decent sized clip is essential for safe surgery – the clip area should be big enough so that if a wound needs to be extended because a cat turns out to be pregnant or there are complications, it will not reach the unclipped hair. Electric clippers are useful, and can be used in most locations with a supply (carry an extension cord) or rechargeable ones pre-charged before leaving your base.

Prepping should be thorough and prolonged – never returning to the centre of the prep are where the incision will be. It is important to ensure the skin is clean and free of hair before scrubbing – but also that the chemical used to prep is safe for skin and actually of the correct ingredients to kill organisms. If you are unsure of the nature of the chemical you are using (look for hibitane or povidone-iodine in the ingredients) then a final scrub with surgical or methylated spirit is ideal.


The sterile drape provides a wide sterile margin around an incision site, preventing contamination from the unprepared areas of the animal (fur etc) touching the surgical wound. Another sterile drape is also used to lay instruments on – the inside of plastic sterile glove wrappers, can also be used if care is taken not to contaminate them before use. The photo on the right is from a week-long field clinic run by a very small charity.

Disposable drapes can purchased pre-sterilised (around $2 US for a set for a cat). These are by far the easiest way to drape – they are of small volume and weight and so can be easily carried if you are visiting an area to volunteer as a surgeon (enough for 50 cats weigh about the same as a t-shirt and take up the same volume in a suitcase as a pair of trousers).

A portable autoclave can also be used (often these can weigh as little as 8kg).

Cloth drapes can be made from old sheets and boiled to sterilize if there is no autoclave – they must be allowed to dry inside the protected vessel before use, as wet drapes will conduct bacteria (airdrying on a line is not safe).

J cloths, for this reason, are totally unsuitable as drapes.


As swabs enter the animal’s abdomen, they must always be sterile when used for surgery. As with drapes, pre-sterilised swabs are easiest to use, are sufficient for 50 female cats,  and will weigh less than a couple of paperback novels so they can be easily carried to the location.

Swabs can also be autoclaved on site with a portable autoclave or in a hot air oven… but as they are absorbent, they cannot be boiled for use as they never dry out!


Instruments entering animals’ abdomens must always be sterile. This can be achieved by autoclaving at a suitable temperature for a suitable time period, or boiling (maintaining them in a continuously boiling vessel for at least 25 minute). Pouring boiled water from a kettle on instruments, will not render them sterile. Boiling or autoclaving has an advantage of conducting heat, meaning that all parts of the instrument are reached.

Instruments should be unclipped in an open position, and free of dirt and blood, before boiling. Even in field locations with no electricity, boiling can be achieved if charcoal or firewood is carried and a small fire created.

Once sterilised, they need to be maintained and transported without touching them – autoclaving inside special autoclave film, or pouches, will allow them to be stored for several days, or if they are going to be used shortly, then autoclaving inside a cloth drape or old pillowcase will work.

Instruments can also be heated in a small hot air oven steriliser – such as that above. In the photo the two large artery forceps on either side are for the non-scrubbed nurse or technician to lift out the sterile instruments with. This is in a temporary field clinic. Any heat-generating device can be used in this way – a small hob cooker with an oven, etc.

Chemical sterilants can be used, but it should firstly be established that the chemical actually renders them sterile rather than just clean or disinfected. They should always be in date, diluted correctly, and applied to the instruments (in contact) for the correct length time.

Chemical sterilants are often irritant or cytotoxic, meaning once they are applied the instruments need to be rinsed off before contact with animals’ tissues. This means that you need either a kettle of boiled water, or a supply of pre-boiled water transported in plastic bottles, to rinse off the instruments.


The surgeon should be scrubbed up correctly, and gloved. Sterile gloves (those individually packed as pairs in sealed packaging) will eliminate almost all the risk of contamination from a surgeon’s hands. The packaging should be intact and in date. Watches and jewellery should be removed and correct scrubbing should be used  – surgeons should know how to scrub correctly before they carry out their first surgeries. Enough gloves for 50 cats or dogs can be easily carried and take the same volume and weight in a suitcase, as a pair of shoes.

Below is an example of poor sterile technique – there is no patient drape, instruments are in contact with the cat’s fur, and the surgeon has her watch on:

More information

This is a very basic guide to sterile processes for field surgery. It has been written deliberately with a view to working in field conditions and is only an introduction.

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