THE PET HEALTH LIBRARY
By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
High Blood Pressure (Systemic
Hypertension) in our Pets
High blood pressure is an extremely important concern in human medicine.
A high stress lifestyle, smoking, and high salt diet all contribute to
this potentially dangerous condition and virtually everyone in the U.S.
knows how serious it can be. But what about our pets? They don’t smoke
or worry about the mortgage and they don’t deposit cholesterol in their
blood vessels. They do, however, get high blood pressure, especially in
age, and here is what you probably should know.
What Does High Blood Pressure Do?
Problems from high blood pressure arise when a blood vessel gets
too small for the high pressure flow going through it. Imagine attaching
a garden hose to a fire hydrant. The pressure would cause the garden
hose to explode and that is what happens to a blood vessel too small
for the pressure going through it. Instead of water going everywhere,
as in the garden hose analogy, bleeding results. Since the affected vessels
are small, the bleeding may not be noticeable but a lot of little bleeds
and a lot of blood vessel destruction can create big problems over time.
The retina of the eye is especially at risk, with either sudden or
gradual blindness often being the first sign of latent high blood pressure.
The kidney also is a target as it relies on tiny vessels to filter toxins
from the bloodstream. Kidney disease is an important cause of high blood
pressure and also progresses far more rapidly in the presence of high
blood pressure.
High blood pressure also increases the risk of embolism: tiny blood
clots that form when blood flow is abnormal. These clots can lodge in an
assortment of inopportune locations including the brain.
What Causes High Blood Pressure in Pets?
There are numerous diseases in pets that are associated with high
blood pressure:
• Chronic renal (kidney) failure In one study, 93% of dogs with chronic
renal failure and 61% of cats with chronic renal failure also had systemic
hypertension.
• Hyperthyroidism In one study, 87% of cats with untreated hyperthyroidism
had systemic hypertension. (Note: hyperthyroidism is a feline disease
only.)
• Glomerular disease is a disease of the kidney filtration system
in which protein is lost in urine. It is important to screen pets with
high blood pressure for urinary protein as control of protein loss is important
to survival time.
• Cushing's disease (an adrenal cortisone excess)
• Diabetes mellitus (inability to properly reduce blood sugar)
• Acromegaly (growth hormone excess)
• Polycythemia (an excess in red blood cells)
• Pheochromocytoma (an adrenaline secreting tumor of the adrenal
gland)
In humans, high blood pressure is frequently considered “primary,”
meaning there is no underlying disease causing it. In animals, primary
hypertension is unusual; there is almost always another disease causing
it and if routine screening does not identify the problem, more tests
may be in order.
How is High Blood Pressure Identified?
In human medicine, high blood pressure is called the silent killer
because most people have no reason to think they might be hypertensive.
To find high blood pressure in people, we screen for it. This means that
virtually any time you see a doctor of any kind, a nurse will take your
blood pressure. Similarly, in pets, a great deal of high blood pressure
is identified by screening. If a pet has one of the above conditions,
blood pressure is generally checked. It has recently been recommended
that older pets have their blood pressure checked whenever they have a
physical examination. If you own a pet over age 9, be sure to ask for a
blood pressure check if it has not been recommended to you.
The other time high blood pressure is discovered is when it makes
its presence known. This usually means some degree of blindness or some
other obvious eye problem. The retina of a hypertensive patient develops
tortuous-looking retinal blood vessels. Some vessels may even have broken,
showing smudges of blood on the retinal surface. Some areas of the retina
simply detach. Sometimes the entire retina detaches. With early identification,
some vision may be restored. Do not let minor vision changes go unreported.
Let your veterinarian know if you think your pet’s vision is not normal.
Retinal changes can be complicated to interpret. Do not be surprised
or alarmed if your veterinarian recommends referral to a veterinary ophthalmologist.
How Do we Measure Blood Pressure in Pets?
Doppler Blood Pressure Monitor
Blood pressure measurement is performed similarly to the way
it is in humans. An inflatable cuff is fit snuggly around the pet’s foot
or foreleg. Sometimes the base of the tail can be used. The cuff is inflated
so as to occlude blood flow through the superficial artery. In a person,
as the cuff is slowly deflated, a stethoscope is used to listen for the
point when the blood pressure is adequate to pump through the partially
occluded vessel. This point on the pressure gauge is the systolic blood pressure.
The cuff is further deflated until the vessel is open and no more sounds
are made. This point represents the diastolic blood pressure.
In animals, the stethoscope is just not sensitive enough and an ultrasonic
probe must be taped or held over the artery. Using ultrasound, the sound
of the systolic pressure is converted into an audible signal. It is not
possible to measure diastolic pressure in a pet without actually placing
a catheter inside an artery so we make do with just a systolic measurement.
In pets, this measurement should not exceed 160. A reading of 180 is considered
by the American College of Veterinary Internal Medicine to indicate high
risk for organ damage.
Some pets (obviously) are nervous at the vet’s office and this factor
must be taken into account when reading blood pressure. It is possible
for a pet to have high blood pressure at the vet’s office and normal pressure
at all other times.
One might think this would be a common situation but most pets are
able to maintain normal blood pressure despite being surrounded by hospital
staff.
To account for the “White Coat Effect,” at least five measurements
are taken so that the pet becomes accustomed to the process and understands
that no pain is involved.
What Treatment is Available for Hypertension?
When ocular disease is present, special eye drops may be required
depending on how much the eye is bleeding and whether or not return of
vision is likely. (Here is one area where an ophthalmology specialist may
be especially able to help.)
When hypertension is identified, a search for the underlying cause
is indicated. It may be that controlling the underlying disease totally
reverses the hypertension (especially true for hyperthyroid cats).
Beyond these methods, as with people, medication to actually lower
blood pressure is often in order. This typically involves some type of
pill that dilates peripheral blood vessels, effectively making them larger
so as to accommodate the high pressure blood flow going through them.
Enalapril, an angiotensin converting enzyme inhibitor, is
the usual first choice for dogs. It is typically given once or twice
daily.
Amlodipine, a calcium channel blocker, is the usual first
choice for cats. It is typically given once daily. These pills are very
small, so we recommend that the owner buy a pill cutter for more accurate
dosing. Alternatively, a compounding pharmacy can create accurately-sized
capsules or even a flavored liquid.
Salt restriction in the diet is controversial; it seems to
make sense but there is not enough data at present to whole-heartedly recommend
it. Certainly, if the pet has kidney disease, the recommendation is less
equivocal as these low salt diets are designed with other features more
specifically for kidney disease. This generally means a dry or canned formula
prescription diet if the pet will eat it or a diet limited to dry food
if the pet will not accept prescription food.
Appropriate home cooked diets may be designed with a veterinary nutritionist
such as Dr. Rebecca Remillard at http://www.petdiets.com.
Hypertensive patients should be rechecked every 2 to 4 months to
keep their blood pressure in a healthy range.
Research on this Topic
Effect of Control of Systolic Blood Pressure of Survival in Cats
with Systemic Hypertension. Jepson, R.E., Elliott, J., Brodbelt, D., Syme
H.M. Journal of Veterinary Internal Medicine 2007; 21: 402-409.
In this study 141 pet cats with high blood pressure were studied.
In these cats, 87% were found to have either evidence of renal failure
(increased BUN or creatinine tests) or hyperthyroidism or both. Amlodipine
besylate was used to treat hypertension in these cats and in 50% of the cats,
the initial dose eventually proved inadequate and an increase was necessary.
Blood pressure was stabilized within one to two recheck visits for 96% of
cats, with a median time of 20 days required to achieve blood pressure stabilization.
Blood pressure was more difficult to control in the long term for cats with
higher urinary protein loss.
Copyright 2007 - 2007 by the Veterinary
Information Network, Inc. All rights reserved.
This work was originally published by Veterinary Information Network,
Inc. (VIN)
and is republished with VIN's permission.
