A raised blood pressure or hypertension, is the leading cause of death and globally it accounts for 10.4 million deaths each year. Furthermore, it is an extremely common condition with the World Health Organisation estimating that 1.13 billion people have hypertension and data from Public Health England suggests that hypertension affects more than 1 in 4 adults in England. Hypertension has been called the ‘silent killer’, due to the lack of any obvious symptoms although some patients attribute their headache or nosebleeds to high blood pressure, but this is largely untrue, unless blood pressure values are extremely high as occurs during a hypertensive crisis.
Control of blood pressure is required since it is one of the most important and modifiable risk factors for cardiovascular disease. In fact it has been estimated that globally, 54% of strokes and 47% of cases of ischaemic heart disease are due to hypertension, and patients are also at an increased risk of myocardial infarction. Hypertension becomes more common with advancing age, and with up to 12 million people in the UK aged 65 years and older, ensuring adequate control of blood pressure is likely to become a major public health challenge over the coming years.
As a healthy living pharmacy status is likely to be become an essential service requirement in 2020/21, to what extent can the community pharmacy team contribute towards both the identification and care of patients with hypertension?
Blood pressure is the force of blood against the artery walls as the heart pumps blood throughout the body. From a mechanistic perspective, blood pressure (BP) is the product of cardiac output (CO) and the peripheral vascular resistance (PVR), i.e., BP = CO x PVR. It follows that a high BP can therefore occur due to either an increase in CO or PVR or both. Under normal circumstances, maintenance of blood pressure is achieved through a balance of CO and PVR and is a complex process with a range of different factors influencing both CO and VP.
Blood pressure is defined by two values: the systolic and diastolic pressures, which are measured in mm of mercury (mmHg). The systolic pressure is the force generated by contraction of the heart when pumping blood through the body whereas the diastolic measures the force of blood against the artery walls as the heart relaxes and refills with blood. A blood pressure reading is reported as a ratio of the systolic/diastolic values.
Causes of hypertension
Despite years of research, the underlying cause of hypertension remains uncertain. In over 90% of cases, there is no easily identifiable cause, and is termed essential or idiopathic hypertension. Nevertheless, one important contributor is disturbance of the renin-angiotensin-aldosterone system (RAAS), which plays a critical role in the regulation of blood volume and peripheral resistance. In this complex system, renin, angiotensin II and aldosterone all interact to elevate blood pressure in response to a reduced renal blood flow. Renin acts upon an inactive target, angiotensinogen, converting it to angiotensin I and, via the enzyme angiotensin converting enzyme, angiotensin I is converted into angiotensin II. This latter agent causes vasoconstriction of blood vessels as well as water and salt retention in the kidneys, and this combined effect increases blood pressure. Finally, angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone which further increases salt and fluid retention in the kidneys.
As discussed earlier, the incidence of hypertension increases with age, though in the majority of patients aged 65 years and older it is an increased systolic, rather than diastolic, pressure that is the most common form of hypertension.
Despite uncertainty over the cause of essential hypertension, there are a range of possible lifestyle contributory factors, and one of the earliest to be identified was an increased salt intake. The impact of salt on hypertension was revealed in a Cochrane review which found that reducing salt intake from around 11.5g/day to 3.8g/day, reduced average systolic and diastolic blood pressures by 5.5mmHg and 2.9mmHg respectively. The impact of other lifestyle factors are discussed later (see Table 2).
Other than lifestyle, other factors implicated as causative in hypertension include genetics and ethnicity, and it is known that African Americans have a higher blood pressure than Caucasian Americans.
In contrast to essential hypertension, an elevated blood pressure can occur as a consequence of other medical conditions, including diabetes, polycystic kidney disease and thyroid disease. In such instances, this is known as secondary hypertension.
Stages of hypertension
In 2019, NICE produced guidelines for the management of adults with hypertension which classified disease severity into three categories as shown in Table 1. NICE has recommended that blood pressure measurements should be performed on both arms and repeated if there is a difference of 15mmHg. In cases where this difference persists after the second measurement, future measurements should be undertaken on the arm with the higher reading. Hypertension can sometimes be detected only during visits to a health professional, and in such cases, home blood pressure measurements should be used to identify those with white coat hypertension, i.e., where there is a marked variation in blood pressure readings taken at home and at a surgery.
Cardiovascular risk assessment and end organ damage
Once hypertension has been diagnosed, NICE recommends that a patient’s cardiovascular disease (CVD) risk assessment is performed, as well as the detection of end organ damage. Cardiovascular risk can be performed using a risk calculator such as QRISK®3 which require input of several relevant factors, including lipid levels, systolic blood pressure, age, ethnicity, smoking status etc. The risk calculator should be used to inform further decisions regarding treatment and the threshold used by NICE was a 10-year CVD risk of > 10%.
The presence of hypertension can result in end organ damage e.g., the heart itself, kidneys, the brain, arteries (atherosclerosis) and eyes. NICE has therefore recommended assessing for heart damage (e.g. left ventricular hypertrophy), damage to the eyes (e.g. hypertensive retinopathy) and the kidneys (e.g. chronic kidney disease). Urine should be checked for the presence of albumin, calculation of the albumin: creatinine ratio, as well as for blood (haematuria). Samples of blood should also be tested for glycated haemoglobin (HbA1C) to assess for diabetes, electrolytes, creatinine, glomerular filtration rates and cholesterol levels.