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Prevalence of bacterial contamination of 50% dextrose vials | VETgirl Veterinary Continuing Education Podcasts

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In today’s VETgirl online veterinary continuing education podcast, we review the prevalence of bacterial contamination in 50% dextrose vials. How worried should we be about using multi-dose dextrose bottles?

Here’s a common emergency scenario: you have a hypoglycemic puppy crashing on your triage table. You instinctively reach for a bottle of 50% dextrose that lives in the treatment area fridge. Now, I’m sure we’ve all had this thought run across our minds, “Is that bottle really still sterile?” With so many hands grabbing it, so many punctures to the rubber stopper, and time the bottle has been left out at room temperature, how sterile are the contents of this repeatedly used single-use bottle? We use dextrose supplementation to manage hypoglycemia in many situations. Some of the more commonly encountered conditions include young, sick pets, sepsis, insulinomas, insulin overdose, and in the management of DKA’s. Despite the fact that these bottles are labeled for single use, most hospitals use them multiple times per bottle and store them in refrigerated conditions hoping that both the solution’s hyperosmolarity and refrigeration will inhibit bacterial growth inside the solution. 50% dextrose has an osmolarity of 2500 mOsm/L, whereas, normal plasma has an osmolarity in dogs and cats of roughly 300 mOsm/L. We can’t give 50% dextrose directly IV without first diluting it as the hyperosmolarity will cause severe phlebitis (VETgirl traditionally dilutes this 1:1 to 1:3 to be safe just prior to administration via peripheral IV catheter!). It’s this degree of hyperosmolarity that is responsible for the relatively sterile nature of 50% dextrose since it is too hyperosmolar for bacteria to thrive. But do we, perhaps, have a false sense of security in this property?

So, Marshall et al out of Purdue University wanted to evaluate this in a study entitled Prevalence of bacterial contamination in 50% dextrose vials in varying storage conditions after multiple punctures. In this study, they assessed the bacterial growth in these 50% dextrose over the course of a month under various storage conditions and multiple punctures. Investigators made 4 study groups with three bottles of 50% dextrose in each group. A 13th bottle was used as a negative control and only opened for culture purposes on day 28. Two groups (A and B) were stored at room temperature (25°C). Group A of the room temperature bottles experienced constant exposure to room lighting, while Group B of room temperature bottles was stored in the crash cart and experienced minimal exposure to room lighting for sampling purposes only. A third group (C) was stored in the refrigerator at 4°C. The first bottle of each group was sampled on day 1 and day 28 by withdrawing 1mL with an 18-gauge hypodermic needle. The stoppers were not wiped with alcohol prior to sampling and gloves were not worn as a way to maximize the risk for contamination of the bottles. The second bottles in groups A, B, and C were sampled weekly for 4 weeks. The third bottles in groups A, B, and C were sampled daily, but only the samples from days 1, 7, 14, 21, and 28 were cultured. A fourth group (D) of 3 bottles was directly inoculated with bacterial microorganisms grown in a veterinary diagnostic laboratory.

Of the Group D bottles, one was stored at room temperature under ambient lighting, another was stored in the dark at room temperature, and the third bottle was stored in the dark and under refrigerated conditions at 4°C inside a light-protective bag. The inoculated bottles were punctured with an 18-gauge needle on days 7, 14, 21, and 28. The handler equipped sterile gloves for their own protection, but the stoppers tops were not wiped with alcohol prior to needle puncture. All culture samples were processed on specialized growth media including blood agar plate, MacConkey agar plate, and thioglycolate broth. The samples were considered negative for growth if no visible growth was seen on the plates at 48 hours, and no visible growth seen in the broth by day 7 of incubation. Only two cultures in the entire study had positive growth. One of the positive cultures was from the group D (the inoculated bottles). The bottle had been stored in a light-protective bag under refrigerated conditions and only the culture from day seven showed growth of E. coli and E. agglomerans. The second positive culture came from a bottle in group C that was kept under dark, refrigerated conditions and receiving daily punctures. The puncture on day 28 showed growth of Bacillus subtilis. It’s interesting that the 2 positive cultures came from bottles stored under refrigerated conditions. The samples were not run in duplicate, so significance of refrigeration on bacterial growth in dextrose is questionable.

The authors theorize that the bacteria in the refrigerated bottles may have created cold shock proteins to help slow their death. The authors also theorize that the growth of Bacillus subtilis may have been the result of environmental contamination after sampling, as this is a prevalent microorganism in the environment and can be airborne. What are some limitations of this study? Samples were not run in duplicate so we have no way of knowing if the sample was contaminated outside the bottle or if the bacteria was in the dextrose solution. The fact that no other samples under any condition grew this bacteria suggests that the sample was contaminated outside the bottle and perhaps on the growth media plates instead of within the dextrose bottle.

The results of this study may have proven that the hyperosmolarity of 50% dextrose cannot be solely trusted to inhibit all bacterial growth. So how worried do we need to be about repeatedly using the same single-use bottle of dextrose? That’s a bit tricky. In the clinical scenario, our bottles of 50% dextrose may become accidentally contaminated from soiled rubber stoppers, soiled hands, and airborne pathogens, so likely the bacterial load would be much less than what was evaluated in this study design. We can’t infer from this study whether the bacterial load from a more clinically applicable situation would be enough to survive such a hostile hyperosmolar environment. We also don’t know how long the bacteria can thrive in these bottles following contamination – is it a mean survival time of minutes? Hours? Days? Perhaps a practical follow-up study would be to sample and culture 50% dextrose bottles within an emergency hospital setting (both large animal and small animal) so we know the bottles will be frequently used, and then to culture them daily or even every few hours.

So, what do we take away from this VETgirl podcast? VETGirl will continue to use caution in sampling and storing 50% dextrose bottles – taking the added safety precautions of wiping the stopper with rubbing alcohol prior to needle puncture and having the handler wear gloves to prevent accidental inoculation. In addition, it may be warranted to set a 48-hour expiration date on opened bottles of 50% dextrose, and then used for only oral dextrose administration thereafter (albeit, this is less commonly used in veterinary medicine). Perhaps we can now store our bottles out of the fridge (which may be nicer for our patient’s thermoregulation), on an easily accessible shelf as well as in the crash cart. As always, please continue to dilute your 50% dextrose prior to intravenous administration to minimize phlebitis – at least 1:1 to 1:4 for IV boluses down to a 5% solution when administered in a peripheral vein (Silverstein) and up to 7.5% or even 10% in a central vein.

References:
1. Silverstein DC, Hopper K. Small Animal Critical Care Medicine 2nd Edition. St. Louis:Elsevier, 2015.
2. Marshall KA, Brooks AC, Hammac GK, et al.Prevalence of bacterial contamination in 50% dextrose vials in varying storage conditions after multiple punctures. J Sm Anim Prac 2018;59:758-762.

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