scott@vtx-cpd.com

Replying to Daphna S. 14/10/2021 - 15:44

Hello.

Harry has popped some answers to your questions below:

1) The RER formula discussed is unfamiliar to me – in my workplace/uni/textbooks I’ve always come across BWx30+70 (for animals between 2 and 30kg). Is this not considered correct anymore or dose the RER calculation in the lecture refer the something else entirely?

– There are a whole range of RER/MER formulas proposed and are frequently updated as new research comes out. A lot of formulas will have an exponential function (i.e. bodyweight) which takes into account allometric scaling – the fact that the calorie requirement of animals does not increase linearly with body weight- i.e. smaller animals need a higher calorie requirement/kg than larger animals.
– The formula(s) in the presentation were taken from the National Research Guidelines- Nutrient Requirements of Dogs and Cats. These guidelines are generally considered the reference source and are an assimilation of years of research into calorie/nutrient/water requirements. However, although the guidelines are often updated, there is a potential for it to be out of date!
– Overall, I don’t think it overly matters which formula is used as they are very rough estimations and vary between dog-dog and on a day-day basis. As long as a rough estimate is made using the formula(s) and then increased/decreased to that individuals animal requirement, it should be fine.
– Personally, I do tend to use the 30*BW+70 formula frequently, principally because some calculators struggle with the exponential (BW0.75) part on other formulas, opening the opportunity for errors. I think it does depend on your individual practice/hospital’s situation whether introducing more complex calculations is feasible, or whether this is going to lead to errors/confusion (which is arguably a more important consideration!).

2). Considering the graphs discussed in the lecture which demonstrate that ‘maintenance rate’ Hartmanns provides x3 times more salt than the animal requires, not having seen in practice any other calculation other than the traditional 2ml/kg/hr, never having seen medications + food being deducted from fluid requirement calculations or calculating for lean body weight and using Hartmanns for the vast majority of our cases (we only stock Hartmanns and 0.9% NaCL) – I’m just wondering whether we’re extremely overloading all out hospitalised patients constantly and hindering their improving and getting better?

– Personally, I think there are two important points with this:
– Firstly, yes, we probably are fluid and salt loading the majority of our animals and overall, we would likely be better moving towards trying to quickly transition onto oral intake of water (cf. intravenous) and monitoring to ensure that animals are maintaining hydration. However, the reality is that we do not have enough research evidence to say how significant the consequences are and unfortunately will be unlikely to be able to carry out such research in veterinary medicine. Furthermore, the risk with intravenous fluids is likely to be of much more importance in animals that are salt/fluid sensitive (i.e. animals with kidney/heart disease) compared to animals that have had a routine operation (i.e. a lipoma removal). When we look at human medicine, there is generally suggestion that fluid overload (and maybe more so than underload) is correlated with a poorer outcome. However, the exact consequence varies between study and are likely at a lower (more nuanced) level than we would be able easily detect in our animals (most veterinary studies have small numbers of participants). For example, in one study looking at Plasmalyte vs. 0.9% Saline in critically ill adults, the 30 day mortality was 818/7942 (10%) in the Plasmalyte group vs. 875/7860 (11%) i.e. using 0.9% Nacl (cf. Plasmalyte) ‘only’ resulted in 1% more deaths. Such a small % difference would be difficult to assess in veterinary medicine and may even be brushed off as an ‘insignificant amount’. However, the other way you could look at this is “yes only 1% more people died with 0.9% NaCl than Plasmalyte, however that was 57 actual people” who died as a result of the using 0.9% NaCl vs. Plasmalyte”. So, yes, although we should be aiming to avoid this, particularly in at risk demographics, the true risk (if any) is currently unknown in veterinary medicine and, most likely, is a relatively small, but not insignificant, risk.

– Secondly, I think the most important question is ‘what is feasibly achievable/manageable for my practice’? I’m a big proponent of ‘minimising cognitive load’. I.e. everyone has a set amount of ‘mental power/energy’ for making decisions and the more things you have to think about (i.e. the bigger the cognitive load) the less mental power/energy you have for other things – potentially opening up the opportunity mistakes. For example, if it is a horrendous Saturday morning clinic where the phones won’t stop ringing, somebody has phoned in sick, the waiting room is full, the label printer has stopped working, the parvo puppy has chewed it’s IV out, and the vet student failed to bring cake on their last day, the more you have going on and the less mental power/energy you have for making decisions. This may mean that, when someone subsequently asks you to draw up medetomidine and butorphanol for a sedation, you draw up 0.5ml of medetomidine instead of 0.05ml by mistake – it happens, everyone is human, everyone has a set amount of mental power/energy and it’s important to minimise the cognitive load to help minimise error. Therefore, if you are in a nice quiet practice where the vet student has remembered to bring cake on their last day then great, you have the time to make it the ‘norm’ to sit down and work out the exact fluid calculation taking into account lean body weight and other sources. Conversely, and probably the situation pretty much everyone is in at the moment (i.e. where the practise is very busy and calculating in-depth fluid calculations is not the norm), I personally think it is more important to have a set, simple rule for everything, to minimise everyone’s cognitive load and avoid errors. However, more detailed fluid calculations could be something that is introduced over time and made easier with flow-charts/calculations sheets/excel forms etc.
– Overall, the presentation is more an example of ‘this is what we should be aiming for’ but must be very much tailored to everyone’s individual situation, especially with the limitations we’re facing at the moment. Long story short – if your practise is too busy to frequently check on in-patients because of the workload, don’t have the time (mental energy) to calculate exact fluid requirements taking into account lean body weight etc., or it is not the ‘norm’ to do so, it’s probably better that the animal goes on 2ml/kg/hr of Hartmann’s to minimise the risk of error and to concentrate on other aspects of care.

3) Would we expect to see changes to electrolytes test results after a certain amount of time on Hartmanns 2ml/kg/hr, due to the high quantities of sodium and chloride, or would results be affected by a much longer increase in intake?
– Again, I don’t think we have any idea of the exact relationship. Anecdotally, I have definitely seen sodium increase in animals on high rates of fluids (and believe the IV fluids was the cause). Most commonly this has been in animals with kidney problems and, off the top of my head, I’ve seen it the most in post-obstructive cases (i.e. blocked cats). It’s always hard as a vet to judge the post-obstructive diuresis phase in blocked animals, but my suspicion is that we generally get it wrong and give them more fluid than is needed. I’ve seen sodium creep up in a lot of these, but more commonly see signs of fluid (rather than electrolyte) overload- i.e. pleural effusion, abdominal effusion, pulmonary oedema etc.

Hope this helps.

Let me know if you have any questions.

Scott 🙂

Thank you so much for this.

I will pass this on to Harry. He will be made up!

Scott 🙂