Hypokalemia (hypo-low, kal-potassium-emia-blood) is a deficiency of potassium in the blood plasma, the straw coloured, liquid part of the blood which makes up approximately 55% of the blood volume. Also known as kalium (with the symbol K), cats obtain potassium through their diet. More than 90% of potassium is found within the body's cells (intracellular), the remainder is present in the extracellular fluid of the blood. Kidneys control levels of potassium by excreting excess out of the body via the urine.
|Normal||Low (hypokalemia)||High (hyperkalemia)|
|4 - 5.3 mmol/L||<3.5 mmol/L||> 5.5 mmol/L|
What is potassium?
Potassium is an essential electrolyte which performs several functions including:
What causes hypokalemia in cats?
The cause can be divided into the following.
- Increased loss of potassium
- Decreased intake of potassium
- Translocation (movement) of potassium from the extracellular fluid into the intracellular fluid
The most common cause of hypokalemia in cats is loss of potassium due to increased potassium excretion in cats with chronic kidney disease (CRD). Vomiting is common in cats with CRF which also leads to further losses.
Inadequate intake of potassium or excessive potassium loss:
- Decreased potassium intake, this may be due to a diet low in potassium, insufficient amounts of food, starvation, or inadequate diet.
- Prolonged vomiting and/or diarrhea can cause systemic losses of potassium.
- Diabetes which can cause metabolic acidosis, decreased appetite and increased urination.
- Hyperthyroidism has been linked to hypokalemia, but the exact mechanism isn't know.
- Certain medications such as diuretics (furosemide) can cause excessive urinary output.
- Over-administration of fluids.
- Post obstructive diuresis in cats who have had urinary blockages treated. Increased urine output occurs as once the obstruction has been removed, the kidneys are able to resume their job of urine production, removing toxins from the bloodstream.
- Primary or secondary hyperaldosteronism (also known as Conn syndrome). The adrenal glands sit on top of the kidneys producing a number of hormones. The outer layer (known as the cortex) produces two hormones, cortisol and aldosterone. The latter hormone, aldosterone is responsible for elevating blood pressure when necessary, during this process, potassium is excreted from the body via the urine. These hormones are usually kept in check, however when aldosterone levels rise abnormally, excessive amounts of potassium can be lost. Primary hyperaldosteronism is caused by a hormone secreting tumour of the adrenal gland(s), secondary can be due to kidney disease, congestive heart failure or liver disease.
- Inherited hypokalemia has been known to affect some Burmese and related cat breeds. This is known as Familial Episodic Hypokalaemic Polymyopathy.
Potassium shifts from the extracellular to the intracellular fluid.
- Administration of sodium bicarbonate to treat metabolic acidosis can cause potassium to be pushed into cells.
- Administration of insulin which drives potassium into cells.
- Glucose administration, which stimulates insulin production, which drives potassium into cells.
What are the symptoms of hypokalemia in cats?
Mild cases of hypokalemia are usually asymptomatic. Symptoms may relate to the underlying cause and not hypokalemia itself.
Cats with moderate to severe hypokalemia will present with symptoms due to low potassium which interferes with the contractibility of skeletal, cardiac and smooth muscles. One of the first symptoms of hypokalemia in cats is severe muscle weakness due to the higher loss of potassium from the muscles compared to other tissues, the heart (also a muscle) is also affected with arrhymias (abnormal heart rhythms).
Other symptoms may include:
- Exercise intolerance.
- Muscle pain (myalgia).
- Stiffened posture and gait.
- Reluctance to move.
- Inability to raise the head due to muscle weakness (ventral neck flexion).
- Increased thirst and urination (due to decreased kidney function).
- Weight loss.
- Muscle wasting.
- Dull coat.
Severe cases can cause death either due to abnormal heart function or paralysis of the respiratory muscles.
Depending on the underlying cause, other symptoms may also be present such as those associated with kidney disease.
How is hypokalemia diagnosed in cats?
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you including any medical conditions your cat may have and medications he may be taking, duration and type of symptoms your cat has displayed. During the examination he will may detect bradycardia (abnormally slow heart beat).
Some tests he may wish to perform include:
- Biochemical profile: Potassium is decreased. In cats with kidney failure, BUN (blood urea nitrogen) and creatinine levels will be elevated.
- Urinalysis to measure levels of potassium in the urine.
- Urine specific gravity to determine how concentrated the urine is as well as evaluate for excess potassium.
- Complete blood count which may reveal mild anemia if your cat has chronic kidney disease.
- Electrocardiogram to determine if hypokalemia has affected normal heart function.
- Genetic testing for Burmese and related breeds suspected having Familial Episodic Hypokalaemic Polymyopathy.
Additional diagnostic tests may also be necessary to find the underlying cause. This may include ultrasound or xrays to evaluate the kidneys and T3 and T4 tests to check for hyperthyroidism.
How is hypokalemia treated?
Treatment is aimed at treating the underlying cause, reducing potassium losses and returning serum potassium levels to normal. This may include:
- Controlling diarrhea and/or vomiting.
- Oral administration of potassium is the safest method of treatment.
- Severe cases will require intravenous administration of concentrated potassium until the cat has become stabilised and potassium levels return to normal, it then may be switched to oral potassium. This treatment does not come without its risks however and careful monitoring of serum potassium levels will be necessary.
- Cats on low magnesium or acidifying diets to treat kidney disease should be avoided in cats with hyperkalemia as they can make the condition worse.
- Regular monitoring of your cat's potassium levels will be required while he is undergoing treatment.
What is the prognosis for cats with hypokalemia?
Most cats who are treated will make a full recovery. An improvement should be seen between 1-3 days after administration of potassium.
Cats with chronic kidney disease will need ongoing treatment to manage the disease. While there is no cure for CRF, progression can be slowed down.