Description 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 and aneroid instruments are being replaced by electronic or Doppler devices.
White coat hypertension and masked hypertension may be particularly relevant in this patient group. One study found that ambulatory blood pressure measurement correlated quite well with home monitoring2and the latter is becoming a validated method.3 Whatever method is used, the instrument must be regularly checked for accuracy and serviced and used correctly.
Epidemiology 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.4 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.
An approximate rule of thumb is 80 + (2 x age) for 50th centile, and 100 + (2 x age) for 95th centile.
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.5 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.6
Hypertension is on the increase due to the rise in obesity in children. One study found that organ damage, such as left ventricular hypertrophy, thickening of the carotid vessel wall, retinal vascular changes and even subtle cognitive changes, were detectable in children and adolescents with high blood pressure and the authors of this study considered that hypertension was a common long-term health problem in this age group.7
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.8Processed 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.9
- Low birth weight - this seems to be a particular risk factor in patients who subsequently have a high BMI.10,11
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:
In older children
If the condition is found, enquiry should be made for certain features in the child's history:
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 ¾ 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 Wilms' tumour and abdominal bruit may suggest coarctation or other vascular abnormalities including in the renal system.
- Virilisation will point to congenital adrenal hyperplasia.
Causes 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:12
| Causes of Childhood Hypertension According to Age Group |
| Age | Causes |
| 1 to 6 years | Renal parenchymal disease; renal vascular disease; endocrine causes; coarctation of the aorta; essential hypertension |
| 6 to 12 years | Renal parenchymal disease; essential hypertension; renal vascular disease; endocrine causes; coarctation of the aorta; iatrogenic illness |
| 12 to 18 years | Essential hypertension; iatrogenic illness; renal parenchymal disease; renal vascular disease; endocrine causes; coarctation of the aorta |
Investigations12 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.
Management1 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 modification1,12
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.14 One study found that the blood pressure reduction of angiotensin- converting enzyme inhibitors, angiotensin II receptor antagonists and calcium-channel blockers was almost identical. In children with pathological proteinuria, angiotensin- converting enzyme inhibitors or angiotensin II antagonists were superior to calcium-channel blockers.15
Management of a hypertensive crisis
An acute hypertensive crisis may be the result of an acute illness, such as glomerulonephritis oracute 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 treatconvulsions in a hypertensive crisis. Suitable drugs include nifedipine, labetalol and sodiumnitroprusside. Newer rapid-acting drugs such as clevidipine have been developed.16 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.17 A Cochrane review concluded that further research was needed to determine which drugs were best for the treatment of hypertensive crisis and their effect on morbidity and mortality.18
Prognosis 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, morbidity or mortality will also strike early.12,19
WILLIAM ARELLANO
Pediatra
facebook.com/ William.Virgo.
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