Hypertension in cats
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Hypertension (both primary and secondary to other diseases such as chronic kidney disease – CKD) is a common disorder, especially in older cats (above 7–10 years of age), but the evaluation of blood pressure and the diagnosis and monitoring of hypertension are complex. In some studies, hypertension has been diagnosed in more than 5% of apparently healthy older cats, emphasising the importance of routine assessment of blood pressure.
Indirect measurement is the only method of clinically assessing blood pressure in conscious cats, but this is as much an art as a science.
Methods for assessing blood pressure
The two commonly used techniques for indirect blood pressure assessment are the Doppler and oscillometric methods. In general, the Doppler method has been regarded as more accurate (more closely representing true or direct blood pressure readings) in conscious cats, but newer generation oscillometric equipment (especially newer high definition oscillometric – HDO – machines) also appear to have acceptable accuracy for measuring systolic pressures in conscious cats.
Diseases associated with hypertension
The majority of hypertensive cats have an underlying disease that predisposes to the condition, and chronic kidney disease (CKD) is the single most common of these, with studies suggesting between 20% and 35% of cats with CKD may have hypertension.
A diagnosis of hypertension may be suspected when a cat has a predisposing underlying disease (such as CKD, hyperaldosteronism, hyperthyroidism) or on the basis of clinical signs associated with so-called target organ damage (signs present in organs that are recognised as being susceptible to the effects of systemic hypertension) such as:
- Sudden onset blindness (retinal detachment)
- Hypertensive retinopathy
- Left ventricular hypertrophy
- Neurological signs
Ideally, hypertension should be diagnosed and managed before systemic effects become clinically apparent, so blood pressure measurement of at-risk cats (including older cats and those with associated diseases) is strongly recommended on a routine basis.
When cats should be treated
Whether Doppler or oscillometric equipment is used to assess blood pressure, measurement of systolic blood pressure (SBP) in cats is considered adequate for clinical assessment, as isolated diastolic hypertension appears to be rare. However, because blood pressure assessment can be affected by so many variables (including the operator, the conditions and environment the procedure is performed in, the equipment used, the position of the cat, and the site of measurement) it is important to use standardised protocols to reduce external variables as much as possible, but once mastered, blood pressure measurement can be a relatively quick procedure in many cats.
It is generally considered that if systolic blood pressure is less than 150–160 mmHg, then the risk of target organ damage is mild to minimal, whereas if systolic pressure is consistently greater than 180 mmHg the risk becomes severe. However, interpretation of blood pressure measurements should take into account the individual cat, risk factors for hypertension, and the circumstances under which blood pressure was measured. It is important to exclude so-called white-coat hypertension (temporary elevations in blood pressure due to stress) to avoid treating cats unnecessarily, and this is a common and important issue in cats.
The International Society of Feline Medicine has recently published practical recommendations on the measurement of blood pressure in conscious cats in order to make these assessments as accurate and reproducible as possible. These recommendations are in the form of a downloadable leaflet (including a blood pressure assessment form) available in a number of languages:
ISFM practical recommendations on the measurement of indirect blood pressure in cats
ISFM Blood pressure assessment form
ISFM hypertension short videos