There is no current standard UK definition of hypertension in children. However, the issue has been researched in some detail in the USA, where a working group in 2004 defined the condition as an average systolic and/or diastolic blood pressure ≥95th percentile for gender, age and height on three or more separate occasions. The working group also introduced the concept of 'pre-hypertension' which it defines as a blood pressure level ≥90th percentile but <95th percentile. European guidance from the European Society of Cardiology uses the same definitions.
Normal blood pressure values for children and adolescents are based on age, sex and height. They are available in standardised tables. These may be simplified into a table which gives an indication of the levels of blood pressure in children and adolescents that require further evaluation.
As with adults, blood pressure varies between individuals and within individuals from day to day and at various times of the day. Attention must be paid to correct technique in measuring blood pressure and with small patients this includes the use of a small cuff. Correct size and placement of the cuff are crucial. The size of cuff that should be used is the largest that fits on to the upper arm and still allows auscultation of the brachial artery. The traditional method of auscultation of first and fifth Korotkoff sounds, using a mercury sphygmomanometer, gives an accuracy that is second only to direct cannulation of the artery. Mercury and aneroid instruments have been increasingly replaced by electronic devices, although the auscultatory method remains gold standard[6, 7].
White coat hypertension and masked hypertension may be particularly relevant in children. One study found home monitoring to be a suitable alternative to ambulatory blood pressure measurement, although few electronic devices are validated in children. Whatever method is used, the instrument must be regularly checked for accuracy and serviced and used correctly.
The prevalence of hypertension in children is increasing due to the rise in obesity in children.
Based on the use of ≥95th percentile to define hypertension, it would be expected that the prevalence of hypertension would be approximately 5%. However, due to regression to the mean with repeated measures, the prevalence of hypertension is lower than 5%.
A study in the USA determined the prevalence of hypertension to be 3.6% and the prevalence of pre-hypertension to be 3.4% in children and adolescents between the ages of 3 years and 18 years. Prevalence of pre-hypertension and hypertension combined in adolescents who are obese in the USA has been found to be over 30% in boys and is 23-30% in girls.
Organ damage, such as left ventricular hypertrophy, thickening of the carotid vessel wall, retinal vascular changes and cognitive changes, is detectable in children and adolescents with high blood pressure. Hypertensive children will often go on to become hypertensive adults, unless a treatable cause is found.
In the absence of overt disease that will cause hypertension, there are a number of factors known to affect blood pressure in children and young adults. These are:
- Salt intake. Processed and convenience foods tend to be very high in salt.
- Obesity. Childhood obesity increases the risk of childhood hypertension.
- Low birth weight. This seems to be a particular risk factor in patients who subsequently have a high BMI.
- Family history of hypertension or cardiovascular disease.
- Male gender.
- Maternal smoking during pregnancy.
Breast-feeding is protective, ie children who have been breast-fed are less likely to become hypertensive.
Hypertension is often associated with the presence of other risk factors for cardiovascular disease, such as high lipid levels and diabetes.
Children are significantly more likely than adults to have secondary (rather than essential) hypertension. Up to 85% have an identifiable cause. Renal disease (parenchymal or vascular) is the most common cause of hypertension in childhood.
- Renal artery stenosis.
- Renal parenchymal disease.
- Coarctation of the aorta.
- Cushing's syndrome.
- Medication or substance or illicit drug effect (amfetamines, cocaine, steroids, caffeine, sympathomimetics).
- Mineralocorticoid excess (congenital adrenal hyperplasia, aldosterone-secreting tumours).
- Obstructive sleep apnoea and sleep disordered breathing.
- Rheumatological conditions.
- Essential hypertension (primary hypertension).
The condition is usually asymptomatic but may be revealed fortuitously during examination in patients with suspected underlying conditions such as kidney disease or coarctation of the aorta.
A very full history is required including:
- Past medical history, including birth, growth, developmental history, and past history of renal, cardiovascular, endocrine or neurological disorders.
- Medication history, including nutritional supplements, over-the-counter medication, and illicit substances
- Sleep history. (Sleep disordered breathing is associated with hypertension.)
- Family history.
- Other cardiovascular risk factors: smoking and alcohol in adolescents, diet and level of physical activity.
- Full systems enquiry to look for an underlying medical condition.
- Symptoms of very high blood pressure (headache, vomiting) or hypertensive emergency (seizures, altered mental state).
Examination is normal in most cases.
- Examination of the child starts with looking at the general state of nutrition and apparent state of health. Check height and weight against centile charts.
- Blood pressure:
- Examination of the pulse precedes measurement of blood pressure.
- The child should be seated and relaxed or supine if a baby.
- The cuff is placed around the upper arm. Measure blood pressure in both arms. If there is a significant difference this may suggest coarctation of the aorta.
- The rubber blade inside the cloth cover should be long enough to encircle the arm or at least 90% of it, and wide enough to cover approximately three quarters of the distance from shoulder to elbow.
- Examine the rest of the cardiovascular system. Check for displacement of the apex beat and signs of left ventricular hypertrophy. Heart murmurs in children may be relevant. Also, feel the pulses in the lower limbs. If the amplitude of the pulse is poor this suggests coarctation of the aorta.
- Look for stigmata of specific diseases:
- Café au lait spots may suggest phaeochromocytoma.
- Examination of the abdomen may reveal a mass in Wilms' tumour and abdominal bruit may suggest coarctation or other vascular abnormalities including in the renal system.
- Virilisation will point to congenital adrenal hyperplasia.
- Acne, hirsutism, central obesity and striae may suggest Cushing's syndrome.
- Sweating and tachycardia may indicate medication or illicit substances as a cause, or thyroid dysfunction if associated with exophthalmos or a palpable thyroid gland.
In children a cause for the hypertension should be sought. Basic screening tests to detect underlying pathology should be carried out together with investigations to assess comorbidity and end-organ damage.
Further testing may be required, depending on individual and family histories, the presence of risk factors and the results of the screening tests. The younger the child is at presentation and the more severe the blood pressure abnormality, the more likely that there is a secondary cause of hypertension.
To identify the cause
- Urine - check for albumin and blood and exclude infection.
- U&Es and creatinine - to assess renal function; low potassium may suggest elevated aldosterone.
- FBC - may reveal anaemia consistent with renal disease.
- Renal ultrasound - to exclude abnormalities of renal morphology.
To identify comorbidities
- Drug screen - this may be relevant in adolescents, to exclude ingestion of recreational drugs.
- Fasting lipids and glucose - to rule out hyperlipidaemia, metabolic syndrome, diabetes.
- Polysomnography - to establish the existence of a sleep disorder, which may be linked to hypertension.
To identify end-organ damage
- ECG - may show left ventricular hypertrophy or strain.
- Echocardiography - can show hypertrophy and abnormal function.
- Retinal examination - may identify retinal vascular changes.
Additional tests as clinically indicated
- 24-hour urine for protein and creatinine, creatinine clearance - to exclude chronic kidney disease.
- Advanced imaging - magnetic resonance angiogram, duplex Doppler flow studies, 3-dimensional computerised tomography, arteriography (classic or digital subtraction), may be required to exclude renovascular abnormalities.
- Ambulatory blood pressure monitoring - may be needed to exclude white coat hypertension.
- TFTs - to rule out thyrotoxicosis.
- Plasma aldosterone - a high concentration is diagnostic of hyperaldosteronism.
- Plasma catecholamines or urine catecholamines and catecholamine metabolites - high levels are diagnostic of phaeochromocytoma or neuroblastoma.
- Plasma renin levels:
- High plasma renin activity indicates renal vascular hypertension, including coarctation of the aorta.
- Very low plasma renin activity suggests glucocorticoid remediable aldosteronism or apparent mineralocorticoid excess.
Hypertension in children and adolescents is treated with lifestyle changes, including weight loss if indicated, a healthy, low-sodium diet, regular physical activity and avoidance of tobacco and alcohol. Children with symptomatic hypertension, secondary hypertension, target organ damage, diabetes or persistent hypertension despite non-pharmacological measures should be treated with antihypertensive medications. In primary school-aged children, medication is rarely needed.
This includes weight control, encouragement of exercise, reduction in dietary sodium and fat and, where appropriate, cessation of smoking and alcohol. It is essential to assess and, wherever possible, modify all cardiovascular risk factors.
Prevention of the problem through healthy lifestyle choices and prevention of obesity is important.
A Cochrane review found sparse data with regard to the use of antihypertensive agents in children. Those studied appeared to be safe, at least in the short term. The best evidence for efficacy in terms of lowering blood pressure was for candesartan; however, studies related to blood pressure-lowering rather than end outcomes.
Acceptable drug classes for use in children with hypertension include angiotensin-converting enzyme (ACE) inhibitors, alpha-blockers, beta-blockers, calcium-channel blockers and thiazide diuretics. There is limited information on the use, in children, of angiotensin-II receptor antagonists - also called angiotensin receptor blockers (ARBs).
Diuretics and beta-blockers have a long history of safety and efficacy in children. ACE inhibitors and calcium-channel blockers have been shown to be safe and effective in short-term studies in children. Refractory hypertension may require additional treatment with agents such as minoxidil.
Management of a hypertensive crisis
- An acute hypertensive crisis may be the result of an acute illness, such as glomerulonephritis or acute kidney injury, drugs or psychogenic substances, or exacerbation of moderate hypertension.
- A hypertensive crisis can present with features of cerebral oedema, heart failure, pulmonary oedema, or acute kidney injury. In younger children there may be irritability, poor feeding, failure to thrive or seizures, whereas older children may be able to report symptoms such as headache, vomiting, dizziness, visual changes or chest pain.
- The accurate assessment of blood pressure is essential when a patient has a seizure, particularly when no epileptic disorder is known.
- Treatment with intravenous (IV) agents is essential for severe elevation of blood pressure in the initial stage.
- Anticonvulsant drugs are ineffective to treat convulsions in a hypertensive crisis. Suitable options include nifedipine, labetalol and sodium nitroprusside. Newer rapid-acting drugs such as clevidipine have been developed.
- The aim is to decrease blood pressure towards normal over 48 hours. Close supervision is required to avoid an excessively rapid decrease in blood pressure that may result in underperfusion.
- This is dependent upon the underlying cause. Experience from adults shows that poorly controlled blood pressure is a risk factor for coronary heart disease and is the major risk factor for stroke.
- Children with raised blood pressure are more likely to become hypertensive adults[22, 23].
- There are no definitive data to link childhood blood pressure with cardiovascular risk but extrapolation of other data would suggest that, if hypertension is poorly controlled from an early age, morbidity or mortality will also strike early. There is evidence that end-organ damage occurs.
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