Asepsis

The text on this page is taken from an informal compilation of opinions of contributors to the online VOLE List. As such, they are not peer reviewed and may contain differences of opinion. Those wishing to contact the list may contact Adrian Smith.

Would anyone be happy to discuss on or offline their policies for asepsis in non recovery/ terminal surgery?

I'm particularly interested what guidelines you have in place for longer procedures (over two hours) and what evidence these are based on. Most of what I can find in the literature focuses on longer surgery/ higher change of bacterial contamination raising risk of post op surgical site infection, it would be good if anyone could share any information on any more subtle physiological effects that might impact data.

We also have one model where a very specialised probe used cannot be sterilised only cleaned (this has been followed up with the manufacturer and no other options are available) so thoughts on pushing for non-recovery surgery that is as clean as possible in circumstances like this would also be very welcome.

For probes and other specialised equipment which can get wet but not be autoclaved (and we have no access to ethylene oxide or irradiation) we use things like Cidex glutaraldehyde solution followed by a rinse with sterile saline.

For things which must be kept dry we use a spray can of air duster, this is also used during recovery craniotomies to get rid of little bone fragments after drilling.

For items that cannot be autoclaved we use vaporised hydrogen peroxide. I have concerns about the ability of the gas to penetrate into every nook and cranny of complex structures (because there is no pre-vacuum phase before "sterilisation"), but in your case it would probably be more effective than just wiping the exposed surfaces.

Regarding probes or other equipment, we also use liquids of the Cidex category. In case there is a part that cannot be sterilized, which is usually the handle, we insert it in a sterile glove or other drape so that the surgeon can hold it.

I well remember an article in Laboratory Animal Science (the precursor of JAALAS) which described sepsis in dogs undergoing non-recovery surgery. The citation is:

Slattum MM, Maggio-Price L, DiGiacomo RF & Russell RG (1991): Infusion-related sepsis in dogs undergoing acute cardiopulmonary surgery. Laboratory Animal Science.

Abstract: During acute cardiopulmonary studies, 33 of 170 (19.4%) dogs developed uncontrollable acidosis accompanied by varying degrees of diarrhea and hypotension. Affected dogs had evidence of gram-negative bacteremia and septic shock. Intravenously administered fluids were contaminated with gram-negative bacteria. Since the experimental procedure entailed nonsurvival surgery, aseptic techniques were not employed.

Although aseptic surgical techniques are to be used in animals undergoing survival surgery, such techniques also may be warranted in non-survival surgeries.

The problem was that the researchers were making their own saline to save money, and over the 2-3 hour non-survival surgeries the dogs were having problems. There were other problems with surgical asepsis, not just the saline.

Here are various papers on bacterial contamination through exposure of surgical site simply to room air. This one indicates 3 x the levels of infection at 3 hours (around 45 CFUs) to that at 1 hour and that "fall out" was quicker than expected - and this is in a clinical aseptic setting.

Quantitatively, the risk for surgical site infection is markedly increased if the surgical site is contaminated with > 105 microorganisms per gram of tissue and somewhere I think this is meant to be at about 4 hours for aseptic surgery from what I remember from vet school (and therefore much sooner if you don't start aseptically). I have a feeling that something came out in the mid-2000s that suggested it was even quicker (which is why I think there was a recommendation to move to aseptic surgery for > 2hours)

This paper which relates to the WHO surgical guidelines has a lot of references for all sorts of aspects of surgery (although the ones I think might be the most informative (114 and 117) are books).

Ultimately, I have always argued to my guys: why not do it aseptically irrespective of the duration - it is the only consistent baseline - so why introduce a variable you can control .... they wouldn't not calibrate a scale or kit in the lab and you're effectively have "uncalibrated" bacterial load with non-asepsis.

There were quite a few publications (and posters that may not appear in Pubmed) in the late 90s about this.  The problems identified seemed to start from around 2 hours onwards even with "clean" surgery - one neuroscientist I worked with was particularly surprised when he saw a poster that indicated significant rises in circulating nitric oxide at this 2 hour point.  That individual was a big help in changing practices on site.

In the world of antimicrobial drug development, the models used show a 2-3 log increase in bacterial count within 2 hours post-infection (and up to 5 log in 9 hours) so the 2 hour range for issues to develop would make sense even if the models are not directly comparable.  Perhaps this literature could be used to help demonstrate just how rapidly sepsis can develop?

How do the scientists know that the degree of sepsis that does develop is consistent between animals?  What is one were more infected than the next?  Aseptic throughout for all non-recovery models (unless specifically studying the impact of infections) is really the only scientifically valid way to go.