Recently when discussing treatment for my cat's Kidney Disease, the vet mentioned that in a laboratory setting, specialized diets specifically for Kidney Diease are better at controlling it than Subcutaneous Fluids. I was wondering if yall could explain exactly why specialized diets are better at this?
gettingvetted here.
Subcutaneous fluids are actually quite poor in achieving any kind of long term relief for kidney failure patients. The idea behind it is that a) kidney failure patients are chronically dehydrated because their kidneys cannot effectively retain water, and b) they cannot properly flush out normal byproducts of metabolism due to their kidney failure which is part of what makes them feel so miserable. So, the SQ fluids supposedly help with rehydration and also with flushing. However, SQ fluids are absorbed quite slowly, over the course of hours. A kidney patient may well need more fluids over the course of those hours than the SQ fluids provide. Additionally, if you really want to achieve flushing of the kidneys, you need quite a high rate of fluids that just isn’t possible with SQ fluids. So, it has a non-zero helpful effect, but doesn’t ever truly achieve what we want.
So, if you really want to achieve those effects, you would need to do one or both of two things: intravenous (IV) fluids, which are far superior in the task of rehydration and flushing, or dialysis, which artificially removes those byproducts of metabolism. IV fluids are much more common just because there are only a handful of dialysis centers for animals in the US and each round will cost you upwards of $10k, whereas IV fluids are typically under $100 and can be performed at any vet clinic. (technically kidney transplants are now available for cats at the University of Pennsylvania vet school, but I digress)
Meanwhile, kidney diets are a marvel of modern medicine. If started early in the course of disease, they can give a cat or dog up to 3-4 years longer comfortable lifespan than if the pet was never on a kidney diet. These essentially reduce the need for flushing out of the metabolism byproducts by reducing the amount of nutrients that result in those byproducts. For example Urea is produced in the liver as a byproduct of protein metabolism. This is one of the byproducts that builds up and causes animals to be miserable. If you reduce the protein in the diet, then naturally there will be less urea for the kidneys to remove and the animal will feel less poorly. Additionally, kidney patients struggle to remove excess phosphorus and sodium from the blood, so the amount of those elements in the food is reduced as well. Meanwhile, kidney patients struggle to retain potassium, so kidney diets are fortified with extra potassium. Obviously these foods would be a very poor diet for a normal animal, but in a kidney failure patient, the basic premise is that kidney disease will kill them much more quickly than a lack of protein will, so you stick to the lack of protein.
