In 1940 it was reported that blood pressure (BP) measurements in humans were higher when taken in a clinical setting, compared with those taken at home (Ayman and Goldshine, 1940). This phenomenon, known as ‘white coat hypertension’, can also be seen in veterinary medicine, where nurses have to measure blood pressure in conscious cats reliably and repeatably, in cats that are often anxious, fractious, or uncooperative. Despite this, blood pressure is a vital tool for veterinary surgeons to either rule in or to exclude many common clinical conditions seen in cats, such as renal hypertension, hyperthyroidism and hypertrophic cardiomyopathy. Once a diagnosis has been made and antihypertensive medication started, veterinary nurses will need to reliably repeat the BP measurements to assess the efficacy of treatment at subsequent check ups (Clapham, 2011).
Systemic hypertension has become increasingly recognised in feline medicine in the last two decades (Gouni et al, 2015). It can be idiopathic in origin, meaning that no other medical cause can be found. Stepien (2011) suggests that primary hypertension can account for up to 20% of feline hypertensive patients. However, secondary hypertension, high BP as a result of another disease process, is much more common. Systemic diseases such as chronic kidney disease (CKD) and endocrine disorders such as hyperthyroidism, diabetes mellitus, hyperadrenocorticism or hyperaldosteronism are regularly associated with systemic hypertension. The most common cause of secondary hypertension is CKD and although figures vary greatly between 20–60% of those cats with CKD and systemic hypertension, it is clear that there is a link between the two (Stepien 2011). Hyperthyroidism is commonly acknowledged as the second most common cause of secondary hypertension (Jepson, 2005). As these diseases are commonly seen in older cats, it is recommended that blood pressure measurement in geriatric cats should be a part of a normal screening process (Pittari et al, 2009; Stepien, 2011; Cannon and Brett 2012). One Belgian study looked at clinical findings in apparently healthy cats, and found that older cats had significantly higher systolic blood pressure (SBP) readings than middleaged cats (Paepe et al, 2013). Paepe et al (2013) also made an interesting link that several of the hypertensive cats were feline immunodeficiency virus (FIV) positive. This link has been made in human literature, but needs more research before being definitively linked in cats (Weiner et al, 2003). For a full list of indications of measuring blood pressure, see Box 1.
Systemic hypertension is a chronic problem that can cause damage to susceptible organs of the body, which are known as target organs (Table 1). These target organs are the kidneys, eyes, central nervous system and heart, and are affected because they are highly vascular or are dependent on autoregulation to control blood flow. Target organ damage (TOD) has been reported in humans, dogs and cats (Stepien, 2010). TOD within the kidney can be seen as a result of the chronic high pressure causing tissue injury. This renal dysfunction can be identified by proteinuria on urinalysis. Ocular changes reported in cats as a result of TOD are acute blindness, hyphaema, and retinal haemorrhage (Brown et al, 2007). Stepien (2011) notes that ocular abnormalities are found in about 40–60% of hypertensive cats. Neurological signs can occur as a result of raised intracranial pressure, and can present as altered mentation, focal facial seizures or photosensitivity. Brown (2007) reports that neurological signs have been recorded in 47% of hypertensive cats.
| Organ | Possible clinical signs |
|---|---|
| Renal |
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| Ocular |
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| Neurological |
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| Cardiac Auscultative findings: |
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Left ventricular hypertrophy can be due to cardiomyopathy or systemic disease, so blood pressure measurement is vital for an accurate diagnosis. Jepson and Syme (2010) report that the clinical signs can include murmurs, arrhythmias and gallop rhythms, and have been reported in up to 85% of cats with systemic hypertension. Nevertheless, it is important to remember that cats can have more than one disease process occurring at any one time.
Which method?
There are different ways to measure BP in cats, and most nurses will be restricted to what is available in practice. Only one relatively recent study has compared oscillometric and Doppler methods in conscious cats (Jepson et al, 2005). While the Jepson et al's (2005) study acknowledges that the Doppler method is technically more challenging, it acknowledges that the skill can be taught quickly. The study concluded that the Doppler method was superior to the oscillometric method due to ease of use, repeatability of results, and diagnosis of systemic hypertension. A more recent study looked at the influence of the person taking the BP (Gouni et al, 2015). This found that only the two most experienced observers (a PhD student and a board certified cardiologist) could repeat their findings for systemic BP. When diastolic measurements were recorded, only the cardiologist could reliably note the pressure measurement.
Another study looked at how well conscious cats tolerated BP measurements from the coccygeal and radial arteries using the oscillometric method (Cannon and Brett, 2012). They found that the coccygeal artery was tolerated better and resulted in fewer measurement failures. Other methods for BP measurement are becoming available, such as radiotelemetric implants and are undergoing tests that seem to show promising results (Martel et al, 2013). However everyday use of these new methods will be restricted in practice due to costs and availability for some time. Therefore currently Doppler is seen to be the preferred method of taking non-invasive BP in conscious cats. However one recommendation is that if both oscillometric and Doppler are available, then the most appropriate for the patient should be chosen, taking into consideration its level of anxiety (Stepien, 2011).
How to take blood pressure
Guidelines were published in 2007 by the American College of Veterinary Internal Medicine (ACVIM) to assist with identification, evaluation and management of systemic hypertension (ACVIM, 2007). These guidelines have become standard practice for studies (Martel et al, 2013) and can help veterinary nurses regulate their own protocol in practice. The ACVIM recommended guidelines can be seen in Box 2.
Below are two possible methods for obtaining blood pressure in conscious cats. This is based on the author's experience of running blood pressure clinics for 6 years within a cardiology service. While some may disagree with what is written below, what is important is that a standardised process is used.
Steps for obtaining BP: Doppler method
Steps for obtaining BP: oscillometric method
Conclusion
Accurate and repeatable BP measurement is a challenge for a busy practice. However, it is a skill that veterinary nurses need to be able to acquire no matter what equipment is available, and whatever the design of the practice. Veterinary surgeons make therapeutic decisions based on the information that is provided, and can only do so if the information is accurate. A standardised format for BP measurements is crucial for reliable and repeatable information, and also for training new staff. A description of how each measurement was taken will allow nurses to tailor, but duplicate formats for the individual patient.