TANYA'S

COMPREHENSIVE GUIDE TO

FELINE CHRONIC KIDNEY DISEASE

 

 

 

METABOLIC ACIDOSIS

 

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What is Metabolic Acidosis?


Symptoms


Diagnosis


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Home > Key Issues > Metabolic Acidosis

 


Overview


  • Metabolic acidosis means that the levels of acid in the cat's body are too high.

  • It is extremely common in CKD cats, usually cats in Stage IV.

  • Symptoms include weight loss, muscle loss, a bony spine and mouth ulcers. All of these symptoms may have other causes too.

  • Fortunately it is relatively easy to treat.


What is Metabolic Acidosis?                                                                               Back to Page Index


 

Metabolic acidosis is a very complex subject which tends to make my eyes glaze over. However, it is thought to occur in 65-75% of cats with kidney failure, so it is important to check for it and treat it if it is present. Fortunately, you don't really need to know too much about it, you simply need to know the basics, i.e. what it is, what symptoms a cat might exhibit, how it is diagnosed, and most importantly, how it is treated.

Essentially, metabolic acidosis means that levels of acid in the cat's body are too high. Acid is produced in the body as a result of diet. In healthy cats, the kidneys help to balance acid levels in the body in two ways:

  1. Bicarbonate ions (which are alkaline) in the kidneys help protect against acid build-up in the body;

  2. Any excess acids that do arise are flushed from the body by the kidneys.

Unfortunately the excessive urine flow of CKD washes the protective bicarbonate ions out of the kidneys. The damaged kidneys may also not flush the acids from the body properly. As a result of these damaged mechanisms, acidity levels in the blood rise (i.e. the body’s pH becomes too low). This is known as acidosis, and can cause muscle wasting and weight loss, particularly lean muscle loss, partly because acidosis prevents the cat's body from using protein properly.

 

"Metabolic" means that the acidosis is caused by kidney failure. This is to differentiate it from another type of acidosis known as respiratory acidosis, which is caused by the lungs not expelling carbon dioxide properly.

 

I know a lot of people get confused by the word "acidosis" and think it is the same thing as excess stomach acid, but that is not the case. Excess stomach acid is a separate problem with different causes and treatments, so please be sure you are dealing with the correct condition. It is possible for a CKD cat to have either excess stomach acid or metabolic acidosis, or both at the same time.

 

One study, Assessment of acid-base status of cats with naturally occurring chronic renal failure (2003) Elliott J, Syme HM, Reubens E & Markwell PJ Journal of Small Animal Practice 44(2) pp65-70, found that metabolic acidosis generally does not occur until the CKD is relatively advanced, i.e. creatinine over 400 international or 5 US. However, some cats on Tanya's CKD Support Group have had metabolic acidosis even with pretty low creatinine levels, and this was also the case with one cat in another study, Acid-base balance of cats with chronic renal failure: effect of deterioration in renal function (2003) Elliott J, Syme HM, Markwell PJ Journal of Small Animal Practice 44(6) pp261-8.

 

Current concepts for the management of chronic renal failure in the dog and cat - early diagnosis and supportive care (2005), a presentation by Dr S Sanderson to the World Small Animal Veterinary Association 30th World Congress, explains more about metabolic acidosis.

 


Symptoms                                                                                                             Back to Page Index


 

Symptoms include:

  • weight loss

  • lean muscle loss

  • a bony spine

  • weakness

  • vomiting

  • twitching

  • mouth ulcers

  • breathlessness. Breathlessness caused by metabolic acidosis is known as Kussmaul breathing.

  • in severe cases you may see seizures (or absences, spacing or zoning out)

All of these symptoms may have other causes, please see the Index of Symptoms and Treatments for more information.

 

Metabolic acidosis can also cause potassium imbalances, bone loss and if severe, heart disturbances. In Renal disease (2006), Dr D Polzin mentions that metabolic acidosis may increase the risk of pulmonary oedema in cats on fluid therapy. In Chronic Renal Failure (2001), he states that "potassium depletion and metabolic acidosis may promote potentially fatal reductions in plasma taurine concentrations in cats."


Diagnosis                                                                                                                 Back to Page Index


 

Despite the many risks and side effects of metabolic acidosis, unfortunately few vets bother to diagnose or treat it - in Current concepts for the management of chronic renal failure in the dog and cat - early diagnosis and supportive care (2005),  a presentation to the World Small Animal Veterinary Association 30th World Congress, Dr S Sanderson states that "at least in veterinary medicine, it appears that metabolic acidosis tends to be undertreated in patients with CKD."

 

This may be because metabolic acidosis can be difficult to measure accurately. Below are the usual tests used to diagnose metabolic acidosis.

 

If a cat has metabolic acidosis, the cat's potassium levels may appear high or normal in blood tests, but may subsequently fall after the metabolic acidosis is treated. You should ensure that your cat's potassium levels are monitored, because Dr D Polzin mentions in Chronic Renal Failure (2001) that "potassium depletion and metabolic acidosis may promote potentially fatal reductions in plasma taurine concentrations in cats."

 

Arterial Blood Gas Analysis


This is the most accurate way of testing for metabolic acidosis, but it can be difficult to find a laboratory where this test can be done, and it requires sedation. It is therefore usually only done at specialist vet schools.

 

Global RPh explains how to interpret arterial blood gas tests.

 

TCO2


TCO2 or total carbon dioxide in the blood is a way of measuring levels of bicarbonate in the body. If TCO2 is low, it can be a sign that the blood's protective bicarbonate levels are depleted from too much acid.

 

TCO2 has to be measured on a special blood gas machine, which not many vets and not all laboratories have. It is also easy to make mistakes in taking the measurement because if the sample is exposed to air, the dissolved gas escapes and makes the reading look lower than it really is. Since it is a tricky test to run, some laboratories, such as Antech in the USA, may only measure it on request (with Antech, you need to ask for Test No. T115).

 

The usual range for TCO2 is about 17 to 23. In Renal disease (2006) Dr D Polzin recommends treating for metabolic acidosis  when tests show the level is below 15 mmol/l on more than one occasion. The Merck Veterinary Manual states that treatment "may be indicated if the animal is severely acidotic (plasma bicarbonate <15 mEq/L) or remains acidotic 2-3 wk after diet change."

 

If your vet or his/her laboratory cannot measure TCO2 at all, ask your vet if it is possible to test for carbon dioxide (CO2) levels instead - if they are low, they may also indicate metabolic acidosis. 

 

Anion Gap


This is the difference between measured concentrations of cations (pronounced "cat-eye-ons") and anions (pronounced "an-eye-ons") in the blood. It is calculated as follows:

 

AG = [Na+ + K+] - [Cl- + HCO3]

 

which in English means:

 

anion gap = [sodium + potassium] – [chloride + bicarbonate].

 

Med Calc will calculate it for you if you input the appropriate values from your cat’s bloodwork. 

 

The normal range for cats is around 10-27, though it does vary greatly from lab to lab. If the anion gap is increased in a CKD cat, it may indicate metabolic acidosis, so if your vet is unable to test TCO2 or CO2, but has checked the anion gap, this may be an indicator (although you need to be aware that there are other causes of metabolic acidosis too which may not be reflected in the anion gap). 

 

Cornell University College of Veterinary Medicine has detailed information on metabolic acidosis and the anion gap.

 

Urine pH


Some vets diagnose metabolic acidosis from the pH levels of the urine but in Renal disease (2006) Dr D Polzin states: "Because urine pH is often insensitive as a means of assessing the need for or response to treatment, it is not recommended for this purpose."

 


Treatment of Metabolic Acidosis                                                                        Back to Page Index


 

Diet


The first step for mild metabolic acidosis is to try to feed a prescription diet. Most renal diets are pH neutral or even slightly alkalinising. If your cat will not eat prescription food, at least try to avoid foods for urinary tract health, which are acidified and therefore not suitable for CKD cats generally and cats with metabolic acidosis in particular.

 

Fluid Therapy


Subcutaneous fluids are used to help cats who are unable to remain hydrated without them. It is therefore not appropriate to give sub-Qs purely in order to control metabolic acidosis. However, if you are already giving subcutaneous fluids,  using Lactated Ringers Solution (LRS) (which is the most commonly used sub-Q fluid for CKD cats) may be sufficient to correct mild acidosis, because the lactate is metabolised by the liver where it is converted to bicarbonate, which helps correct the acidosis.

 

Potassium Citrate


Cats with both low potassium and metabolic acidosis can be given potassium citrate. In fact, Dr D Polzin says in Renal disease (2006) that other treatments for metabolic acidosis in cats who also have low potassium may only be of limited use. Potassium citrate is an effective treatment for both problems but you may need to watch for crystals forming in your cat's urine.

 

If you are using potassium citrate, you should give it at least two hours apart from any phosphorus binders containing aluminium, because citrate may increase the absorption of aluminium.

 

Potassium citrate should also not be used or its usage should be stopped for cats with high potassium levels. 

 

Bicarbonate of Soda


Bicarbonate of soda or baking soda (sodium bicarbonate) may be used to treat metabolic acidosis. It works by replenishing the bicarbonate lost from the body. It is available in powder form in the baking section of most supermarkets. In the USA, you can also buy it in pill form, in which case you would probably have to crush it before use.

 

Dosage


Dr Katherine James of the Veterinary Information Network suggests an initial dose of 5-10mg per kg of body weight every twelve hours. A kg is 2.2 lbs, so a 10 lb cat weighs 4.55 kg. A cat of this weight would be given 22.75 - 45mg of bicarbonate of soda every twelve hours.

 

In Renal disease (2006) Dr D Polzin suggests a similar but slightly higher initial dose of 8 to 12 mg/kg body weight every 8 to 12 hours. A 10lb (4.55kg) cat would thus receive 36 - 55 mg of bicarbonate of soda every 8 to 12 hours.

 

You can either dissolve the bicarbonate of soda in a small amount of water and syringe it into your cat's mouth several times a day, or you can give it in a gelcap.

 

When Thomas was first diagnosed, he had metabolic acidosis and my vet recommended giving him the following to drink:

  • 10 fluid ounces (0.3l) of water

  • 2 tbsps powdered glucose (available from pharmacies)

  • 1 pinch of salt 

  • 1 pinch of bicarbonate of soda

Not every cat will drink this but it may be worth trying so ask your vet about it. The cat does not have to drink the entire amount each day. You should not allow cats without metabolic acidosis to drink this, so if you have more than one cat, it might be better to give it to your cat separately (see above). If your cat's metabolic acidosis is severe, it would probably be safer to give more accurate dosages as outlined above. Be guided by your vet.

 

To measure the bicarbonate of soda, see Medicating Your Cat and double check with your vet.

 

Bicarbonate supplementation slows progression of CKD and improves nutritional status (2009) de Brito-Ashurst I, Varagunam M, Raftery MJ & Yaqoob MM Journal of the American Society of Nephrology 20(9) pp2075-2084 found that " bicarbonate supplementation slows the rate of progression of renal failure to ESRD and improves nutritional status among patients with CKD." This was a study with human patients.

Sodium bicarbonate to slow the progression of chronic kidney disease (2011) Rossier A, Bullani R, Burnier M & Teta D Revue médicale suisse 7(284) pp478-82 reports that three trials with CKD indicated that sodium bicarbonate may slow the progression of CKD in humans.

 

It is not clear whether treating the metabolic acidosis generally or the use of bicarbonate of soda specifically helped in these studies. Never give your cat bicarbonate of soda without your vet's knowledge and approval, since too much can cause the opposite problem of excess alkalinity, which can be very dangerous. 

 

Drugs has some information about bicarbonate of soda.

 


Links                                                                                                                         Back to Page Index


 

Acid-base balance: an overview (2007) Morse H, Webb JL & LeRoy BE is a paper from the University of Georgia College of Veterinary Medicine.

Cornell University College of Veterinary Medicine - lots of detailed information on metabolic acidosis and the anion gap.

Veterinary Information Network - Dr Katherine James’ teaching notes on acid base disturbances.

Acid-base, electrolytes and renal failure (1999) Polzin DJ, Osbourne CA, James K Supplement to Compendium on Continuing Education for the Practising Veterinarian 21 11(K)) has information on metabolic acidosis and CKD.

 

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This page last updated: 25 October 2011

Links on this page last checked: 16 April 2012