Why Is My Dog Or Cat’s Blood Pressure High or Low?

Why Is My Dog Or Cat’s Blood Pressure High or Low?

Ron Hines DVM PhD

See What Normal Blood & Urine Values Are

The Causes Of Most Abnormal Blood  & Urine Tests

See How Tests Are Grouped

 Older thin cat? Check for hyperthyroidism

  It is exceptionally hard to get accurate blood pressure measurements on cats and apprehensive dogs. For instance, rest assure that a cat that meows pitifully or soils itself in its carrier on the way to your veterinarian is going to have a high blood pressure reading when it gets there. Read all about that here 

Your Pet’s Blood Pressure – up Hypertension low = Hypotension

In us humans, blood pressure often rises first and our general health suffers later. But veterinarians do not believe that that type of arterial “hardening” (arteriosclerosis/ atherosclerosis) is common in dogs and cats.

Instead, our dogs and cats sometimes suffer from secondary high blood pressure (secondary hypertension) that is the result of health issues that indirectly affect the pressure in  their circulatory system. You can read about some of those problems in an article I wrote some years ago here.

As in people, the early effects of persistent high blood pressure can be easily missed. Perhaps your veterinarian might notice increased snake-like loops and curves in the blood vessels deep within your pet’s eyes (“retinal capillary tortuosity“). More likely, your vet discovered it using a blood pressure monitor during a routine examination or after learning that your pet had kidney issues.

High blood pressure has a particularly destructive effect on the eyes of pets. With time, it can lead to blindness (detached retinas and hemorrhage within the eye , retinal edema,  glaucoma  and retinal degeneration).

High blood pressure eventually affects the brain and nervous system of pets as well. It might begin with behavioral changes (altered mentation), decreased awareness (cognitive dysfunction) and “tipsiness” (ataxia) and progress eventually to seizures.

Many clients tell me their dog or cat has had a “stroke”. That is actually quite uncommon in pets because, as I mentioned, dogs and cats rarely develop the type of blood vessel disease (atherosclerosis) that we do. But stokes do occasionally occur in hypothyroid dogs or dogs born with the tendency to high blood fat (= lipids cholesterol,   triglycerides) levels (hyperlipidemia). 

It is considerably more difficult to obtain accurate blood pressure measurements in dogs and cats than it is in humans. Using the measurement machines currently available  (doppler or oscillometric), it takes a series of measurements to allow the pet to calm down (the ‘white coat” syndrome) and obtain an accurate reading. A second confirmation of high blood pressure a week or two later is always a good idea. 

Health Problems That Can Cause High Blood Pressure (= systemic hypertension) In Your Pet’s General Circulation:

Chronic kidney failure is the most common cause of elevated blood pressure in dog. Up to 80% of dogs with kidney (glomerular) disease are reported to have higher than normal blood pressure. Sudden kidney failure (acute renal failure) is a less common problem – but it can have the same effect.

In cats, hyperthyroidism and feline kidney failure are high on the list of causes. In dogs, an overactive adrenal gland (Cushing’s disease can also result in high blood pressure. Over half of Cushing’s disease dogs are said to have high blood pressure.   Adrenal gland or pituitary gland tumors (those that produce aldosterone or growth hormone respectively) can also elevate your cat or dog’s blood pressure.

Increased blood pressure can also be a side effect when your pet has diabetes. In dogs here.   In cats here.

On rare occasions, dogs and cats have elevated blood pressure when no underlying health problem can be found – but not nearly to the extent that this occurs in people. Vets see that unexplained form most often in cats of certain breed lines – so it is most likely a genetic problem.

Health Problems That Can Cause Elevated Lung Circulation Blood Pressure (= Pulmonary Hypertension):

Another type of high blood pressure in pets is pulmonary hypertension. In that situation, blood pressure increases in the blood vessels going from your pet’s heart to its lungs.

In dogs in my part of South Texas, the most common cause for that is a massive heartworm infection (caval syndrome). However, birth defects (patent ductus arteriosis = PDA) and chronic lung disease can also cause this condition.

Occasionally, failing hearts or lack of oxygen supply to the pet’s kidneys (renal hypoxia) or kidney cancer lead to increased red blood cell production, high PCVs (= polycythemia) and thick (“overly viscous”) blood. That too can cause pulmonary hypertension.

Whichever the cause in your pet, this problem often results in rapid breathing (= hyperpnea), weakness, bluish gums (=cyanosis) and, occasional, fainting and seizures after exertion or exercise. 

Health Problems That Can Cause Low Blood Pressure (Hypotension) In Your Pet:

Unlike high blood pressure which can exist unnoticed in your pet for an extended period of time, low systemic blood pressure in dogs and cats is often a crisis situation.

Pets suffering from low blood pressure often have a weak or irregular pulse. Their heart rate can be fast (tachycardia) or slow (bradycardia). Their gums can be pale and slow to refill when they are pressed (slowed CRT). They are usually “out of it”, that is dull, apathetic and weak, and their feet and ears are often cold. They do not pass much urine.

Pets with low blood pressure are often taken to emergency clinics in need of immediate help. In those situations, simply feeling the strength of the dog or cat’s pulse in its groin or lower leg is usually all that is required to know that it is in need of assistance. 

Here Are Some Common Causes:

Failing hearts (congestive heart failure or  cardiomyopathies) , severe infections (septic shock) , an Addison’s disease crises, severe  blood loss anemia,   anaphylactic shock, prolonged seizures (= status epilepticus) can all be responsible for low blood pressure. 

Severe trauma such as car accidents or animal fights,  severe diarrhea or vomiting (or any other cause of severe dehydration (=hypovolemia), burns and heatstroke can also cause your pet’s blood pressure to drop.

Low blood sugar (hypoglycemia, as occurs with too large an insulin dose given to diabetic pets) can also cause a sudden drop in blood pressure.

Moderately lowered blood pressure has also be seen in hypothyroid dogs.

Anything that restricts the flow of blood through your pet’s heart (like gastric volvulus pressure on the diaphragm, air free in the chest (pneumothorax) or fluid surrounding the heart (pericardial tamponade) can cause abnormally low blood pressure as well.

In some cases of heartworms,  even though the pet’s pulmonary (lung) blood pressure rises (hypertension) systemic (body) blood pressure falls (hypotension).   

Late stage liver failure can also result in low blood pressure as can an abnormal heartbeat (arrhythmias)  , electrolyte imbalances and acid-base disturbances.

Low blood pressure has the ability to activate the clotting process throughout your pet’s body (= activation of the coagulation cascade) resulting in dangerous blood clots.

Medications your pet receives can also be responsible for low blood pressure. Drugs give to treat heart disease (but in excessively large doses) are the most common ones that do that (e.g. beta blockers (like metoprolol, propranolol and atenolol), calcium channel blockers (like amlodipine, verapamil and diltiazem) and ace inhibitors (like enalapril and benazepril). All anesthetics used for general surgery have the potential to lower blood pressure as well. 

Overly large dose of amitriptyline in cats being treated for urinary spraying or dogs for anxiety can also lower blood pressure.

Furosemide (Lasix®) and spironolactone diuretics in dogs and cats can also cause blood pressure to drop, as can  sildenafil (Viagra®) given for pulmonary hypertension.

Complementary Tests That Come To Mind:

The possible results of long-term elevated blood pressure in your dog or cat include kidney, heart and eye damage (ie, visual problems, large pupils, retinal detachment, blood leakage into the eye). Elevated blood pressure can also affect your pet’s ability to think clearly (= forgetfulness, aimless wandering,circling, seizures). So tests to check for any of those problems in your dog or cat – as well as medications to bring blood pressure down – are often warranted when your veterinarian has confirmed a persistently high blood pressure reading.

Blood pressure measurement (you must confirm results on several occasions), CBC and a blood chemistry panel, urinalysis, examination of the dog or cat’s retinas for evidence of hemorrhage, screening test values that focus on kidneyadrenal gland and thyroid health . Review of the pet’s medications and medication doses,  further tests as suggested by the blood chemistry results, physical exam, imaging and the history you provide to your veterinarian.


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