Systemic hypertension is an extremely common and relevant condition in human medicine and large sums of money and expertise are used constantly to improve the understanding of this condition, in an attempt to better diagnose and treat it. It is estimated that 20% of the world's human population is affected. Conversely, in veterinary medicine, attention to hypertension is fairly recent and unfortunately frequent monitoring of blood pressure is still underperformed, because at the initial stages, hypertension causes no specific clinical signs. Clinicians are therefore not alerted to it and diagnosis is only made if its presence is theoretically suspected or routine monitoring is performed. It is therefore crucial to raise awareness of this condition in order to detect hypertension before severe damage occurs.

Definition

Hypertension is defined as persistently elevated systemic systolic (SBP) and/or diastolic (DBP) blood pressure, but the value at which this is considered abnormal cannot be strictly defined and the patients' clinical signs and end-organ damage should always be taken into consideration before further diagnostic or therapeutic measures are taken. Current recommendations consider a SBP of more than 160 mmHg or a DBP of more than 100 mmHg worthy of further investigation, although the use of antihypertensive medication may not be always warranted in the initial stages. The significance of elevated DBP is less well studied in veterinary medicine and therefore more attention is played to the SBP results.

Measurement of Blood Pressure

There are several methods used to measure blood pressure and these can be classified as direct and indirect. Direct measurements are performed via an arterial catheter and this is most commonly used intraoperatively or in an intensive care setting. In the clinical setting of diagnosis, monitoring and management of systemic hypertension, indirect methods are more commonly used. Two basic technologies are available and validated for use in dogs and cats, consisting of oscillometry and Doppler ultrasonography. Accurate measurement of blood pressure is absolutely crucial for the appropriate management of affected patients and the veterinary nursing profession has a pivotal role in this, as in the human field. The measurement of blood pressure is not technically challenging, but accuracy is greatly increased with practice and strict methodology. All effort should be made to minimise the stress or anxiety (fear or excitement) associated with a visit to a veterinary clinic, as this could falsely increase the blood pressure, in a syndrome often referred to as 'white coat hypertension'. The following protocol is recommended:

 The same quiet and comfortable area should be used for the measurement of blood pressure, and the assistance of the owners can sometimes be beneficial.

 The patient should always be allowed to become acclimatised to the room and people for 5-10 minutes before starting the examination.

 Sedation should be avoided.

 The patient should be gently restrained in a comfortable position (generally ventral or lateral recumbency) and the cuff placed on a limb or tail, depending on the patient's acceptance or user preference. The patient should remain calm and motionless.

 The cuff size should measure 40% of the cuff site circumference. Larger cuffs than recommended will under-estimate the blood pressure and small cuff tend to over-estimate it.

 During measurement, the cuff should be maintained at the same level as the heart.

 The first measurement should be discarded and an average of three to seven consecutive measurements should be obtained.

 A detailed record of the results, method, limb (tail) and cuff size used, therapeutic protocol, patient's position, stress level, person performing the measurement and the restraint should be kept for future correlation and better interpretation.

The talk will focus on these recommendations and the published guidelines will be reviewed, with the assistance of videos demonstrating good practice.

Causes and Manifestations of Hypertension

The majority of human patients with hypertension have primary (essential) hypertension with no obvious underlying cause. This differs greatly from the veterinary scenario, where the great majority of patients (>80%), develop hypertension secondary to another disease. Dogs typically develop systemic hypertension in association with renal failure, diabetes mellitus and hyperadrenocorticism, while in cats, hyperthyroidism, renal failure and diabetes mellitus are most commonly responsible. More unusual conditions also associated with hypertension include, phaeochromocytoma and primary hyperalderosteronism. Systemic hypertension is certainly more prevalent in aged patients but obesity, although commonly associated with hypertension in humans, appears to have only little effect in veterinary patients.

Sustained elevated SBP creates a multitude of clinical injuries (target organ damage; TOD) affecting mainly the kidneys, eyes, brain and the heart. The rationale for the treatment of hypertension is to prevent these from occurring. SBP of more than 180 mmHg represents severe risk for significant TOD and emergency treatment can sometimes be indicated.

Target Organ Damage

Renal disease can be the cause or a consequence of systemic hypertension and clinical assessment of renal function is imperative. This should always include biochemistry, haematology and urinalysis with measurement of urinary protein:creatinine ratio. Urinary protein loss is a marker of hypertensive renal TOD and its magnitude correlates directly to the severity of hypertension and with a worse prognosis. Necessary tests should be performed to adequately rule out other causes of hypertension. Ophthalmic evaluation should also be performed as retinal oedema and/or haemorrhage, progressing sometimes to detachment (hypertensive retinopathy) is a common ocular TOD. Milder changes like increased retinal vessel tortuosity, can in some cases raise awareness for the possibility of early hypertensive stages. With the increased availability of advanced imaging techniques, such as magnetic resonance imaging (MRI), an increasing number of cerebrovascular accidents commonly referred to as 'strokes' have been identified in dogs and cats, and hypertensive patients represent a high-risk group for the development of such conditions.

Cardiac evaluation can sometimes be warranted, especially if evidence of heart failure and/or arrhythmias are present. The heart suffers the effects of persistent hypertension as it has to work harder to overcome the elevated blood pressure, resulting primarily in ventricular hypertrophy and consequently to heart failure. A common misconception is that a cardiac condition could cause hypertension. This is never the case. Cardiac disease tends to produce hypotension, as the heart function declines and, in the presence of hypertension, cardiac disease is always a consequence and never the cause of the elevated blood pressure.

Treatment of Hypertension

Once the diagnosis of systemic hypertension is achieved and treatment is agreed, several drugs can be used as a single-drug treatment or in combination, but treatment for the underlying condition, primarily responsible for the high blood pressure, should always be pursued. The drugs more commonly used for the management of systemic hypertension include angiotensin-converting enzyme (ACE) inhibitors, which are the first-choice in dogs, and calcium channel blockers, commonly given as the first line of treatment in cats. Diuretics, beta-blockers and direct vasodilators can also be used. Sodium restriction is commonly recommended in human medicine but its use in veterinary medicine is more controversial. High dietary salt should always be avoided but there is no evidence that substantial sodium restriction plays a beneficial role in the management of hypertension in veterinary patients and may actually, in specific situations, increase BP and lead to progression of undesirable changes. A well balanced diet, adequate for the patient's age and underlying condition, with moderate exercise, is probably more beneficial.

After initiation of therapy, regular follow-ups are advised to optimise its results and monitor for progression or development of significant side effects, such as hypotension. The follow-up protocol should be tailored to each patient, depending on the severity of his/her condition and also taking the owners' availability into consideration. Systemic hypertension management is a chronic process and owner compliance is crucial. All efforts should be made to optimise this.

The increasing awareness and interest surrounding veterinary hypertension is recognised and further advancement in the understanding, diagnosis and management of this significant disease will certainly follow. Assessment of blood pressure is certainly becoming part of the mainstay clinical care for our patients and should be considered an essential part of geriatric screening clinics.

References

1.  Brown S, Atkins C, Bagley R. Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. Journal of Veterinary Internal Medicine 2007; 21(3): 542-558.

2.  Henik RA, Dolson MK, Wenholz LJ. How to obtain a blood pressure measurement. Clinical techniques in small animal practice 2005; 20(3): 144-150.