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An update on hypertension

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Blood pressure was first measured by Stephen Hales in 1773. It is defined in simple mathematical terms as the product of cardiac output and total peripheral vascular resistance. The ideal blood pressure in an uncomplicated individual is 120/80mmHg. Blood pressure between 121-139 systolic, or 80-89 diastolic is defined as prehypertension. Anything higher than this is classed as hypertension, or high blood pressure.

 

The estimated European prevalence of hypertension is 26.3 per cent, of which only eight per cent is thought to be adequately controlled. The NHANES study in the US calculated a similar rate of control, revealing 34 per cent of known hypertensives to have a healthy blood pressure. 20 per cent of the worldwide population have been diagnosed with hypertension.

Half of all people over the age of 65 years have hypertension, an even more significant statisitic when considering that the current population is an aging population, and an increasingly obese population, itself a risk factor for the illness, as well as a contributor to many other morbidities associated with having high blood pressure.

 

Establishing hypertension in a patient is a little more complicated than a simple sphygmommanometer reading. A high blood pressure should be recorded on at least three separate occasions, over a period of up to three months, to exclude incidental or white coat hypertension. And on each of the minimum three visits, blood pressure should be measured twice, with an interval of approximately five minutes. Blood pressure readings will decrease by up to 10 – 15mmHg between visits one and three with a new doctor. Consistency in technique and equipment should be ensured, and it can be a good idea to have a nurse perform the test if possible. This has been shown to further reduce the risk of white coat hypertension.

 

The optimal interval for screening for hypertension in an undiagnosed patient is unknown. The USPS TF guidelines recommend screening for high blood pressure in adults aged 18 years and older. Their recommended interval is dependent on the patient’s blood pressure. If blood pressure is <120/80mmHg, screen at two-year intervals, and if it is 120-139/80-89, then screening at one year intervals has been recommended

 

Hypertension is qualified as essential or secondary, with prevalence of 95 per cent and five per cent, respectively. Secondary hypertension, where the direct cause of the elevated blood pressure is known, should be considered at the initial diagnosis, and later in management if hypertension becomes inexplicably resistant to treatment, but non-compliance with medications should always be considered the most likely reason for resistance and ruled out first.

 

A negative family history is also important. Treatment of secondary hypertension will be medical or surgical. Conservative management
is effective for both essential and secondary hypertension, and is recommended as the only treatment required in the pre-hypertension phase of the disease, which illustrates the importance of measuring blood pressures in younger age groups. In the uncomplicated adult patient, any blood pressure up to moderate hypertension can be treated conservatively initially if benefits are likely. Blood pressure >160/95mmHg should be medically managed from the outset, if no contraindications.

 

In the case of systolic and diastolic blood pressures being in different ranges, the highest range applies. In isolated hypertension, only treat medically if the diastolic blood pressure is greater than 65mmHg. Anything lower warrants caution and investigation prior to treating. When managing a patient over 50 years of age, systolic blood pressure is a more important risk factor than diastolic. Cardiovascular risk doubles for every 20/10mmHg increase in blood pressure above 115/75mmHg.

 

Target blood pressure in an adult with no underlying associated co-morbidities is 0.25g/day, stroke or transient ischaemic attack (TIA). In a patient with associated co-morbidities other than proteinuria, or any end-organ damage, the target is 1g/day with or without diabetes mellitus, the target is <125/75. A hypertensive crisis is the only time hypertension can be diagnosed with a single reading of blood pressure. This type of hypertension is usually a result of IgA nephropathy, drugs or an exacerbation of moderate-severe hypertension. It manifests as cerebral oedema, seizures, acute onset heart failure, acute or flash pulmonary oedema, acute renal failure, intracranial haemorrhage, hypertensive encephalopathy or aortic dissection.

 

Treatment is with intravenous nicardipine, labetalol or sodium nitroprusside if unstable. If the patient is stable, oral dihydropyridine calcium channel blockers (CCBs) can be used. If evidence of myocardial ischaemia, use a beta-blocker with or without a dihydropyridine CCB. Given the likelihood of end-organ damage, avoid overly rapid lowering of blood pressure, causing organ hypoperfusion. Aim for a reduction of <25 per cent in the first two hours, a blood pressure of 160/100 between hours two to six, and be satisfied with this level for 24 hours before further reduction.

Investigations

 

Once diagnosed and evaluated clinically, there are investigations that can be helpful prior to and during treatment of hypertension. Investigations for all chronic conditions should begin simply, advancing to noninvasive and then to invasive. The sphygmommanometer is the beginning of the lifelong illness. A 24-hour or ambulatory blood pressure measurement is indicated if poor control, non-dippers (when blood pressure doesn’t lower appropriately in sleep, often a sign of secondary hypertension), and as mentioned, white-coat and masked hypertension are suspected. Sleep studies will help to diagnose sleep apnoea. A urinalysis will show blood and/or protein in the urine in renal parenchymal disease, as well as leucocytes, important in a child who may develop hypertension secondary to chronic pyelonephritis.

 

A more complex urine study will check for red cell casts or catecholamines. A drug screen can also be useful, particularly in a hypertensive crisis. Blood testing measures salts, creatinine, and renin (increased in renovascular hypertension), aldosterone, thyroid stimulating hormone, catecholamines and uric acid (important because of the association of gout with metabolic syndrome, and because thiazide diuretics are contraindicated with it). Fasting lipids and glucose indicate other cardiovascular risks.

 

Standard and trans-thoracic echocardiogram (ECG) will show left ventricular hypertrophy. An echo has the additional benefit of being able to further evaluate the hypertrophy and the left ventricular function, as well as search for coarctation of the aorta. Abdominal ultrasound may show a renovascular structural abnormality, including tumours, renal size and scarring. An abdominal CT can investigate
the same pathologies and is useful if strongly suspected disease is missed on ultrasound.

 

Renal doppler studies, digital subtraction arteriography and angiography with renal artery sampling for renin secretion are far more sensitive investigations for renovascular disease, though not widely available in Ireland. Renovascular stenosis can be suspected clinically with an unexplained creatinine rise, a negative family history of hypertension, onset of hypertension before puberty or over the age of 50 years, a sudden creatinine increase following initiation of ACE inhibitor or angiotensin II receptor blocker (ARB) therapy, and a unilateral small kidney.

 

Hypertension should be viewed in the context of the overall risk factors of the patient when managing. As with all things medical, high blood pressure is managed conservatively, medically, and on occasion, surgically. However, if the patient has significant risk factors, they should be treated with an appropriate anti-hypertensive even with a blood pressure of 120/80mmHg. If no underlying cause or asociated co-morbidity are identified, conservative management is recommended initially up to moderate hypertension, and is the
only recommended management in pre-hypertension.

 

A reduction of 2mmHg in overall blood pressure can reduce the risk of coronary artery disease by six per cent, and the risk of stroke by 15 per cent. These are simple statistics that can help to improve patient motivation, a crucial element in treating hypertension.

Therapy

 

When selecting initial therapy, take into account the patient’s other cardiovascular risks, associated conditions, and the potential side-effects and contraindications of the medication. Commencing with a single drug at a low dose is usually recommended. Switching to an alternative suitable class of drug is possible if there is an unsatisfactory lowering of blood pressure, or the patient develops side-effects. Switching from an ACE inhibitor to an ARB for a patient who develops a dry cough is a simple and classic scenario. A patient who is unresponsive to one class of drug has a 50 per cent likelihood of adequate response to an alternate, and a 60-80 per cent chance if a third choice is required.

 

Monotherapy has a long-term success rate of 20-30 per cent. A patient with blood pressure greater than 20/10mmHg of the target blood pressure (dependent on co-morbidities) pre-treatment is very likely to require an additional hypertensive, and some guidelines see no harm in prescribing two anti-hypertensives as first-line management. Importantly, with anti-hypertensives, prescribing half the standard dose, where the standard dose has been described as the usual maintenance dose in reference pharmacopoieas, gives the largest reduction in blood pressure.

 

A 2009 meta-analysis of randomised trials found that the average reduction in systolic blood pressure over 24 hours for half-standard, standard and twice standard was 7.1mmHg, 9.1mmHg, and 10.9mmHg, respectively. It recommended titrating a drug up to half the standard dose and then consider adding an additional antihypertensive if required. This will decrease the rate of side-effects. Thiazides, CCBs, and beta-blockers had significant increases in side-effects when increased from halfstandard dosing. This was not the case for ACEI/ARB, which were shown to be dose-independent and have a low rate of side-effects

 

If using combination therapy, a lying/standing blood pressure should be checked at baseline to assess for postural drop or orthostatic intolerance in the patient at risk. This includes elderly, diabetic, alcoholic or haemachromatosis patients who may have lost carotid sinus or aortic arch baroreceptor sensitivity. First-line is considered to be long-acting ACEI/ARB plus dihydropyridine CCB. A CCB can substitute in for a thiazide diuretic if the patient has already been started on an ACEI/thiazide combination. If a diuretic is indicated, use ACEI/ ARB or beta-blocker in combination.

 

Where beta-blocker is required, use either a dihydropyridine CCB or thiazide diuretic. As beta-blockers reduce renin levels, ACEI/ARB don’t work well with them.

 

Doctors should be aware that in some cases some patients can be successfully weaned off antihypertensives. It has been shown that up to 55 per cent of patients will remain normotensive for at least one to two years with full discontinuation of medications. Just reducing the number and/or dosage of anti-hypertensives yields an even larger percentage of patients remaining normotensive for this period.

 

References on request


Dr Michael Carmody

House Medical Officer

Monash Medical Centre

Melbourne

Victoria

Australia

 

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