Hypertension in Childhood

There is no current standard UK definition of hypertension in children. However, the issue has been researched in some detail in America were 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 3 or more separate occasions.¹ The working group also introduced the concept of 'pre-hypertension' which it defines as a blood pressure level ≥90th percentile but <95th percentile.

As with adults, blood pressure is a variable parameter in children. It 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. The traditional method of auscultation of 1st and 5th Korotkoff sounds, using a mercury sphygmomanometer gives an accuracy that is second only to direct cannulation of the artery. Nowadays mercury instruments are replaced by aneroid ones for health and safety reasons and electronic or doppler devices are gaining popularity. Whatever instrument is used it must be regularly checked for accuracy and serviced and used correctly.

A Department of Health Survey for England in 1996 showed that the mean systolic blood pressure for both boys and girls aged 5 to 15 was 111 mmHg.² Mean diastolic pressure was 57 mmHg in boys and 58 mmHg in girls. Mean pulse pressure was 58 mmHg in both boys and girls aged 5 to 15. Blood pressure increases with age in childhood, and children who are either heavier or taller or both have higher blood pressure than smaller children of the same age.³ The relationship between body mass and blood pressure in children is stronger than in adults, and children who have high blood pressure and are taller and heavier than their peers are more likely to become hypertensive as adults.⁴

Risk Factors

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 This is very important and targets to reduce our intake may not go far enough.⁵ Processed and convenience foods tend to be very high in salt.
• Obesity Childhood obesity increases the risk of childhood hypertension. The Bogalusa Heart Study derived figures from several national studies and found that the odds ratios in obese children were 2.4 for raised diastolic blood pressure, and 4.5 for raised systolic blood pressure.⁶
• Low Birth Weight This seems to be a particular risk factor in patients who subsequently have a high BMI.⁷

History

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.
There are a few presenting features that should raise the possibility of hypertension.

In neonates:

• Failure to thrive
• Convulsion
• Irritability or lethargy
• Respiratory distress
• Congestive cardiac failure

In older children

• Headaches
• Fatigue
• Blurred vision
• Epistaxis
• Bell's palsy

If the condition is found, enquiry should be made for certain features in the child's history:

• Prematurity
• Bronchopulmonary dysplasia
• History of umbilical catheterisation
• Head or abdominal trauma
• Familial diseases - e.g. neurofibromatosis, hypertension and multiple endocrine neoplasia, especially if associated with pheochromocytoma.
• History of pyelonephritis may have been missed - ask about pyrexia of unknown origin as urinary tract infection in children is not always overt.
• Medication may have a pressor effect including steroids, amphetamines for attention deficit hyperactivity disorder, children abusing drugs.
• Ask about diet, looking for high salt intake and possibly high consumption of liquorice.

Examination

• 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.
• Examination of the pulse precedes measurement of blood pressure. The child should be seated and relaxed or supine if a baby. The cuff is on the right arm at the level of the heart. The rubber blade inside the cloth cover should be long enough to encircle the arm and wide enough to cover approximately ? 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 very 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 pheochromocytoma.
  • Examination of the abdomen will reveal a mass in Wilm's tumour and abdominal bruit may suggest coarctation or other vascular abnormalities including in the renal system.
  • Virilisation will point to congenital adrenal hyperplasia.

In general, the younger the child and the higher the blood pressure the greater the chance of identifying the cause. 80% are due to renal parenchymal abnormality. The table gives the order of frequency of the various causes of hypertension in 4 age groups:⁸

Most adults are deemed to have essential hypertension and little or no further investigation is undertaken but 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 co-morbidity 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.

To identify the cause

• Urine - check for albumin and blood
• Urea, electrolytes and creatinine - to assess renal function; low potassium may suggest elevated aldosterone
• Full blood count - may reveal anaemia consistent with renal disease
• Renal ultrasound - to exclude abnormalities of renal morphology

To identify co-morbidities

• 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 renal disease
• Advanced imaging - magnetic resonance angiogram, duplex Doppler flow studies; 3-dimensional computed 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
• Thyroid function tests - 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 pheochromocytoma 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.

There are no consensus UK guidelines on the management of hypertension in children. American guidelines suggest that lifestyle modifications should be applied to all hypertensive paediatric patients, and that drugs are indicated in patients who fail to respond to lifestyle measures or have secondary hypertension, symptomatic hypertension, co-morbidity or end-organ damage.

Lifestyle modification^1,8

This includes weight control, encouragement of exercise, reduction in dietary sodium and fat, and where appropriate cessation of smoking and alcohol.

Drugs

American guidelines suggest starting with one drug and increasing the dose until a therapeutic effect is achieved or side effects develop, at which point a second drug should be added. There is little experience in using combination drugs in children. There is little comparative evidence so the choice of drug depends on the physician's preference plus any secondary causes or comorbidities.

• Thiazides and beta-blockers These have the best track record in terms of safety and efficacy.
• ACE inhibitors and calcium channel blockers These are gradually gaining preference as first-line drugs in view of their low side effect profile. Caution may need to be exerted when using ACE inhibitors in patients with renal disease, but they can be helpful in some cases.
• Angiotensin receptor antagonists Their role is currently being evaluated.⁹

Management of a Hypertensive Crisis

An acute hypertensive crisis may be the result of an acute illness, such as glomerulonephritis or acute renal failure, drugs or psychogenic substances, or exacerbation of moderate hypertension. A hypertensive crisis can present with features of cerebral oedema, seizures, heart failure, pulmonary oedema, or renal failure. The accurate assessment of blood pressure is essential when a patient has a seizure, particularly when no epileptic disorder is known. Anticonvulsant drugs are ineffective to treat convulsions in a hypertensive crisis. Suitable drugs include nifedipine, labetalol, and sodium nitroprusside. The aim is to decrease blood pressure to normal within several hours. Close supervision is required to avoid an excessively rapid decrease in blood pressure that may result in underperfusion.¹⁰

This is dependent upon the underlying cause. Experience from adults shows that poorly controlled blood pressure is a risk factor for CHD and is the major risk factor for stroke. There is 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 that morbidity or mortality will also strike early.^8,11