Prevalence of Hypertension in Children

In infants and young children, systemic hypertension is uncommon, with a prevalence of <1%, but when present, it is often indicative of an underlying disease process (secondary hypertension). Severe and symptomatic hypertension in children is usually due to secondary hypertension. In contrast, the prevalence of primary essential hypertension, mostly in older school age children and adolescents, has increased in prevalence in parallel with the obesity epidemic. Approximately 10% of U.S. youth overall have prehypertension and 4% have hypertension. The influence of obesity on elevated BP is evident in children as young as 2-5 yr old. Approximately 20% of American youth are obese, and up to 10% of obese youth have hypertension.

Definition of Hypertension

The definition of hypertension in adults is BP ≥140/90 mm Hg, regardless of body size, sex, or age. This is a functional definition relating level of BP elevation with the likelihood of subsequent cardiovascular events. Since hypertension-associated cardiovascular events such as myocardial infarction or stroke usually do not occur in childhood, the definition of hypertension in children is statistical rather than functional. The National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents published the Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents (Fourth Report) in 2004. This report established normal values based on the normative distribution of BP in healthy children and included tables with systolic and diastolic values for the 50th, 90th, 95th, and 99th percentile by age, sex, and height percentile. These normative tables can be obtained free online at www.nhlbi.nih.gov/guidelines/hypertension/child_tbl.htm. The Fourth Report defined hypertension as average systolic blood pressure (SBP) and/or diastolic blood pressure (DBP) that is ≥95th percentile for age, sex, and height on ≥3 occasions. Prehypertension was defined as average SBP or DBP that are ≥90th percentile but <95th percentile. In adolescents beginning at age 12 yr, prehypertension is defined as BP between 120/80 mm Hg and the 95th percentile. A child with BP levels ≥95th percentile in a medical setting but normal BP outside of the office has white coat hypertension.

The Fourth Report further recommended that if BP is ≥95th percentile, then the hypertension should be staged. Children with BP between the 95th and 99th percentile plus 5 mm Hg are categorized as stage 1 hypertension, and children with BP above the 99th percentile plus 5 mm Hg have stage 2 hypertension. Stage 1 hypertension, if asymptomatic and without target organ damage, allows time for evaluation before starting treatment; whereas stage 2 hypertension calls for more prompt evaluation and pharmacologic therapy (Fig. 439-1).

Figure 439-1 Management algorithm. BMI, body mass index; BP, blood pressure; Q, every; Rx, prescription; † diet modification and physical activity; ‡ especially if younger, very high BP, little or no family history, diabetic, or other risk factors.

(From National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents, Pediatrics 114[2 Suppl 4th Report]:571, 2004.)

Measurement of BP in Children

The Fourth Report recommended that children 3 yr or older should have their BP checked during every health care episode. Selected children <3 yr old should also have their BP checked, including those with a history of prematurity, congenital heart disease, renal disease, solid organ transplant, cancer, treatment with drugs known to raise BP, other illnesses associated with hypertension, or evidence of increased intracranial pressure. The preferred method is by auscultation and a BP cuff appropriate for the size of the child’s arm should be used. Elevated readings should be confirmed on repeat visits before determining that a child is hypertensive. The BP should be measured with the child in the sitting position after a period of quiet for at least 5 min. Careful attention to cuff size is necessary to avoid overdiagnosis, as a cuff that is too short or narrow artificially increases BP readings. A wide variety of bladder sizes should be available in any medical office where children are routinely seen. An appropriate sized cuff has an inflatable bladder that is at least 40% of the arm circumference at a point midway along the upper arm. The inflatable bladder should cover at least two thirds of the upper arm length and 80-100% of its circumference.

Systolic pressure is indicated by appearance of the 1st Korotkoff sound. Diastolic pressure has been defined by consensus as the 5th Korotkoff sound. Palpation is useful for rapid assessment of SBP, although the palpated pressure is generally about 10 mm Hg less than that obtained via auscultation. Oscillometric techniques are used frequently in infants and young children, but they are susceptible to artifacts and are best for measuring mean BP.

Ambulatory blood pressure monitoring (ABPM) is a procedure where the child wears a device that records BP frequently, usually every 20-30 min, throughout a 24 hr period while the child goes about usual daily activities, including sleep. This allows calculation of the mean daytime BP, sleep BP, and mean BP over 24 hr. The physician can also determine the proportion of BP measurements that are in the hypertensive range (BP load) and whether there is an appropriate decrease in BP during sleep (nocturnal dip). ABPM is particularly useful in the evaluation for white coat hypertension and may also be useful for determining risk of hypertensive target organ damage, evaluating resistance to pharmacologic therapy, and evaluating patients with hypotensive episodes on antihypertensive medication. ABPM is also useful for certain special populations, such as children with chronic kidney disease, where it may provide important information on cardiovascular risk that cannot be determined as well by office measurements.

Etiology and Pathophysiology

BP is the product of cardiac output and peripheral vascular resistance. An increase in either cardiac output or peripheral resistance results in an increase in BP; if one of these factors increases while the other decreases, BP may not increase. When hypertension is the result of another disease process, it is referred to as secondary hypertension. When no identifiable cause can be found, it is referred to as primary (essential) hypertension. Many factors, including heredity, diet, stress, and obesity, may play a role in the development of primary hypertension. Secondary hypertension is most common in infants and younger children. In general, the younger the child, the higher the BP and the presence of symptoms related to hypertension, the more likely there will be an underlying secondary cause of hypertension. Many childhood diseases can be responsible for chronic hypertension (Table 439-1) or acute/intermittent hypertension (Table 439-2). The most likely cause varies with age. Hypertension in the premature infant is most often associated with umbilical artery catheterization and renal artery thrombosis. Hypertension during early childhood may be due to renal disease, coarctation of the aorta, endocrine disorders, or medications. In older school-aged children and adolescents, primary hypertension becomes increasingly common.