Definitions

Normative BP ranges in adults have been based on long-term, end-organ risk as determined by large-cohort epidemiologic data. In children and adolescents, normal BP ranges have been defined based on data from relatively large cohort studies in presumed-healthy subjects and are stratified by gender, age, and height. The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC7) and the Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents (Fourth Report) (NHBPEP) define hypertension in children and adolescents as an average SBP or DBP at the 95th percentile or above for gender, age, and height on three or more occasions. BPs (SBP or DBP) between the 90th and 95th percentiles have historically been referred to as “high normal” but in these most recent guidelines have been redefined as prehypertensive. This change reflects the addition of prehypertension to the adult diagnostic criteria as defined by JNC7; there is increased risk of developing hypertension in those with prehypertension. Stage 1 hypertension is defined as a BP above the 95th and up to 5 mm Hg over the 99th percentile for gender, age, and height. Stage 2 hypertension is more than 5 mm Hg higher than the 99^th percentile. More timely antihypertensive therapy is recommended for stage 2 hypertension.

White coat hypertension is defined as having a BP consistently above the 95th percentile for age in a physician’s office or clinic but being normotensive outside of the clinical setting. This diagnosis usually requires ambulatory BP monitoring for confirmation.

There are many causes of hypertension (Figure 47-1). Whereas BP for which a clear cause can be determined is described as secondary hypertension, hypertension without a clear correctable cause is referred to as primary or essential hypertension. This is necessarily a diagnosis of exclusion.

Figure 47-1 Causes of hypertension.

Physiology

BP is determined by both cardiac output (CO) and systemic vascular resistance (SVR). Factors increasing output or resistance can result in hypertension. The relationship between BP and CO is summarized by the following equations.

Multiple causes of secondary hypertension are shown in Figure 47-1. Each condition may increase BP via increases in heart rate, SV, or SVR. Considering these three fundamental factors in BP elevation aids in the appropriate therapeutic approach to a given patient.

Measurement of Blood Pressure

Accurate and consistent measurement of BP is a precondition to appropriate medical management. BP measurements, even when performed correctly, demonstrate significant variability. As a result, the arithmetic mean of three or more BP measurements on separate occasions is used to diagnose hypertension. The mean BP of multiple measurements most closely approximates those obtained by ambulatory BP monitoring.

Accepted epidemiologic statistics for BP are all based on measurements made by auscultation. Despite this, oscillometric measurements of BP are increasingly used because of their ease of use and the (false) perception that they are more precise. Oscillometric “measurements” of SBP and DBP are based on proprietary algorithms that extrapolate these from measured mean BPs. These estimates have been shown to be consistently at least 5 to 10 mm Hg higher than those measured by auscultation. Because of this, high BPs derived from oscillometric measurements should be repeated by auscultation as a matter of course.

Cuff Size and Location

Cuff size also dramatically affects the BP measurement. Cuffs that are too small overestimate BP, and excessively large cuffs may underestimate BP. However, the range of the underestimation with a large cuff is generally smaller in magnitude than errors from very small cuffs. The correct cuff size can be obtained by insuring that the inflatable bladder has (1) a width that is approximately 40% of the arm circumference (or ≈25% greater than the diameter of the arm) at the point midway between the olecranon and acromion and (2) enough length to cover 80% to 100% of the arm circumference. The length-to-width ratio should be approximately 2 : 1, which is not true of all commercial cuffs.

For appropriate auscultation, the stethoscope should be placed over the site of the brachial pulse proximal and medial to the cubital fossa below the distal border of the cuff. Measurement using the bell (instead of the diaphragm) produces superior discrimination of the Korotkoff sounds. The SBP corresponds to the pressure at which the first Korotkoff sound is audible, and the DBP corresponds to the pressure at which the fifth Korotkoff sound is audible or with obliteration of the last sound. If sounds are still heard at 0 mm Hg, a repeat BP should be attempted with less pressure on the stethoscope head.

The measured BP should be compared against BP tables that have been published by the American Academy of Pediatrics, which are normalized for gender, age, and height percentile.

Diagnostic Approach

Before making a diagnosis of hypertension, it is important to rule out immediate causes of transient BP elevations such as acute pain, anxiety, or medication exposure. After such causes have been ruled out, the diagnostic approach in a patient with hypertension can be organized as follows: (1) define the degree of hypertension, (2) investigate end-organ damage, and (3) evaluate for possible causes of secondary hypertension (see Figure 47-1).

Primary or essential hypertension is generally characterized by stage 1 hypertension, is often associated with family history of hypertension or coronary vascular disease, and frequently coincides with obesity. Because of the well-documented comorbidity of hypertension, obesity, hypercholesterolemia, and insulin insensitivity, screening for these other cardiovascular disease risk factors is sensible. Currently, a fasting lipid profile and fasting glucose are recommended as initial screening tests. There are not sufficient data at present to recommend testing plasma uric acid, homocysteine, or lipoprotein A in children with high BP.

Secondary, as opposed to primary, hypertension is more common in children than adults, in whom primary or essential hypertension is overwhelmingly the most common cause. Generally, secondary hypertension is more likely in patients who (1) have stage 2 hypertension, (2) are young (i.e., not adolescents), and (3) have signs or symptoms of systemic disease or have a personal or family medical history of those conditions. As summarized in Figure 47-1, there are numerous causes of secondary hypertension. The history and physical examination should screen for signs and symptoms of causes of secondary hypertension. The physical should include a measurement of height and weight to calculate body mass index. Upper and lower extremity BPs must always be measured. Additional studies should be tailored to the individual patient based on their presentation. Studies should be divided between those seeking the cause of secondary hypertension and those that identify the stigmata of hypertensive end-organ damage.

In patients with stage 2 hypertension, it is important to immediately screen for signs and symptoms of end-organ damage. Hypertensive urgency refers to high BP without evidence of end-organ damage Hypertensive emergency is defined as having acute, end-organ dysfunction, such as neurologic symptoms, vision changes, cardiac chest pain, or acute renal failure, in the setting of marked hypertension. Hypertensive urgency and emergency require immediate intervention to control BP.