By Dr. Dorrie Jordan, Kulshan Veterinary Hospital
Most people are familiar with the dangers of high blood pressure in people. What a lot of people do not know is that dogs and cats can suffer from high blood pressure or hypertension as well.
High blood pressure arises when blood vessels become too narrow for the high-pressure flow going through them. This can cause blood vessels to rupture, resulting in bleeding. Over time, bleeding from these tiny vessels can create big problems.
The retina of the eye is especially at risk. Sudden or gradual blindness is often the first sign of hidden high blood pressure. The kidneys are also targets, since each kidney relies on very small vessels to filter toxins from the blood stream. Kidney disease can cause high blood pressure, but hypertension can also cause kidney disease to progress more rapidly.
Some causes of hypertension in animals include chronic kidney disease, hyperthyroidism in cats, glomerular disease in the kidneys, Cushing’s Disease (an adrenal gland problem), and diabetes mellitus. Primary hypertension is very rare in animals – another disease almost always causes it.
The most common sign of high blood pressure is some degree of blindness. We may see enlarged, tortuous blood vessels in the retina, or the retina may simply detach. If treated early enough, some vision may be restored.
To identify high blood pressure, your pet needs to be tested. Pets with any of the previously listed conditions should be checked for high blood pressure. Some recommend that all older pets be screened; due to the insensitivity of the equipment used to check for hypertension in animals, not every senior pet needs to be tested.
Blood pressure measurements are taken in a fashion similar to that used in people; however a stethoscope is not sensitive enough to check blood pressure. A cuff is inflated to occlude an artery and then an ultrasonic probe is held over the artery. The probe converts the sound of the systolic pressure into audible sound. Diastolic pressure cannot be checked in animals without having a catheter in an artery, so vets only measure systolic pressure.
Blood pressure should be checked before examinations or other tests are performed, to avoid additional stresses affecting the reading. Multiple readings are done to make sure that there are consistent results. Normal systolic blood pressure should be below 160. Readings over 180 mean the animals are at high risk for organ damage.
Controlling hypertension may be done by controlling the underlying disease, such as hyperthyroidism, or the hypertension itself may need to be treated to reduce damage to organs.
In dogs, ACE (angiotensin converting enzyme) inhibitors such as enalapril or benazapril are usually the first choice of drugs to lower the blood pressure. In cats, the first choice is usually amlodipine, which is a calcium channel blocker. Sometimes the ACE inhibitor and amlodipine are used together. Hypertensive patients should be rechecked every two to four months to maintain normal blood pressure.