Although hypertension is a relatively uncommon disorder in pediatrics, its identified incidence is increasing, likely related to both heightened clinician awareness of the problem and increasing rates of obesity in children mediating earlier onset of high blood pressure.^1-4 With adults, most hypertension is deemed to be primary or “essential” in etiology and often no diagnostic evaluation ensues. In children, on the other hand, primary hypertension has long been a diagnosis of exclusion and there has been consensus that hypertensive children need to undergo an evaluation to exclude any secondary causes to their hypertension, especially in the setting of significantly elevated blood pressures for a child’s age and body habitus.

Regardless of its cause, depending on the degree of elevation and the duration of onset, hypertension can lead to both acute and chronic organ dysfunction. In ambulatory settings, otherwise healthy hypertensive children have been found to be more likely to have left ventricular hypertrophy, accelerated atherosclerosis, proteinuria, and decreased cognitive function. In hospitalized children, hypertension may complicate the management of co-existing clinical conditions and there is the additional burden of determining whether the high blood pressure is a primary problem or whether it stems from an ongoing condition or its treatment.

Accordingly, a child who presents with hypertension often requires treatment while the diagnostic evaluation is ongoing. The approach to the evaluation and treatment of hypertension is often both more directed and more intensive in a hospitalized child than in an ambulatory setting. The extent of the blood pressure elevation and the degree of clinical concern for immediate harm to the child from the hypertension also guides the tempo of diagnostic evaluation and therapeutic intervention.

MEASUREMENT OF BLOOD PRESSURE

Blood Pressure Norms

With adults, blood pressure standards are based on epidemiologic outcome measures related to chronic end-organ damage seen in patients followed longitudinally with high blood pressure. In contrast, hypertension standards in children are based on statistical population norms since end organ effects may take decades to manifest. Currently, the “Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents”⁵ is used widely in North America to define blood pressure norms in children, and is more comprehensive than previously published standards.⁶

In children, normal blood pressure is defined as blood pressure measurements consistently falling below the 90th percentile compared to a pediatric reference group of comparable gender, age, and height. Prehypertension (formerly known as high-normal blood pressure) is defined as blood pressure at the 90th percentile or higher but less than the 95th percentile. Stage One Hypertension is defined as blood pressure at the 95th percentile or greater, and Stage Two Hypertension—or what used to be called severe hypertension—is that exceeding the 99th percentile.

Auscultation versus Oscillometry

Accurate measurement of blood pressure is essential before any management decisions are made. Statistical blood pressure norms in pediatrics, such as those in the Fourth Report, are based on measurement by auscultation using a stethoscope. In spite of this, especially in hospitalized children and increasingly in the ambulatory office setting, oscillometric automated devices (e.g. Dynamap) are widely used to measure blood pressure because they are convenient and easy for any personnel to use.

It is often not appreciated, however, that oscillometric measurements of blood pressure are typically at least 5 to 10 mmHg higher than those obtained by auscultation.⁷ This is true even in the hands of experienced clinical staff specifically trained to take blood pressures.⁸ As a result, blood pressure assessment by oscillometry is best used for screening, but any high blood pressure measurements should be confirmed with auscultation to make sure oscillometric readings can be used to guide therapeutic intervention.

Cuff Size and Location

Cuff size is another important factor that impacts accurate blood pressure measurement. Cuffs that are too small tend to overestimate blood pressure, and cuffs that are too large may underestimate blood pressure, although not as significantly as the overestimation resulting from small cuffs. The most precise method for choosing an appropriate cuff size is controversial,^9-11 but the recommendations of the National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents should be considered.⁵ Those guidelines delineate that the width of the cuff bladder should be at least 40% of the arm circumference measured midway between the olecranon and the acromion. This generally correlates with the bladder length covering 80% to 100% of the arm circumference. Appropriate-sized cuffs should be available from infant up to thigh-sized cuffs. In muscular or obese adolescents with large upper extremities, a thigh cuff may be necessary to cover the arm adequately.

Cuff location can also significantly affect the blood pressure reading. Measurements on the upper arm should be made with the cuff at the level of the heart, whether the patient is in the upright or supine position. When the cuff is placed on the lower extremity, the patient should be supine for accurate measurement. The measurement will be elevated due to increased hydrostatic pressure if obtained on the lower extremity of a patient in a sitting or upright position.

Auscultation Technique

As noted earlier, auscultation is the preferred way to measure a child’s blood pressure and should be done to confirm hypertension. With the child at rest and acclimated to the local environment, the examiner places the diaphragm of the stethoscope over the brachial artery at the antecubital fossa. The right arm is used both for convenience and to allow the diagnosis of coarctation of the aorta; the left subclavian artery usually comes off the aorta after a thoracic coarctation and thus has normal blood pressure. The examiner inflates the cuff to a pressure above which a pulsatile sound can no longer be auscultated, at which point the cuff is deflated slowly. The systolic blood pressure is measured at the onset of the tapping, or what is termed the first Korotkoff sound; the diastolic blood pressure is measured at the disappearance of the Korotkoff sounds. In some children, the Korotkoff sounds may continue until the diastolic blood pressure reaches zero. Although this is unlikely in the presence of significant hypertension, if it occurs, the diastolic blood pressure should be measured at the muffling or fourth Korotkoff sound.

Ambulatory Blood Pressure Monitoring

Over the past decade, there has been increasing use of ambulatory blood pressure monitoring to overcome the problems inherent in trying to diagnose hypertension from sporadic blood pressure measurements alone. These devices provide a 24-hour log of blood pressures measured at regular intervals during normal activities. They also allow for assessment of diurnal variations in blood pressure for comparison with expected fluctuations, and provide a sense of the proportion of both systolic and diastolic blood pressures that are elevated, and the extent of these elevations. In the ambulatory setting, these devices can help distinguish between “white coat hypertension”—high blood pressure related to the medical office visit—and true sustained hypertension. In the hospitalized child, these devices have less applicability since it is easier to get multiple measurements by auscultation or oscillometry. Moreover, with the hospitalized patient, there is often more urgency in treating blood pressure elevations and erring on the side of overtreatment if there are concerns that blood pressure elevation may be clinically harmful.

As the incidence of obesity rises, so does the incidence of hypertension in children and the likelihood that children with hypertension will be cared for in the hospital.¹² The etiology of hypertension in obese children is not clear, though many believe insulin resistance and subsequent vascular endothelial dysfunction play a key role. As a result, some argue that obesity-related hypertension is really a secondary form of hypertension and should not be lumped with primary hypertension in children.

Regardless of body habitus, all children with evidence of sustained or recurrent hypertension should be evaluated for secondary hypertension in an individualized and stepwise fashion, guided by the findings on history, physical examination, and initial screening tests. Children with more significant and sustained elevations of blood pressure, as well as younger children, are more likely to have some specific cause of hypertension identified during the evaluation. The most common cause of secondary hypertension in children is renal parenchymal disease,¹³ and the diagnostic evaluation should reflect this. An algorithm for the diagnostic evaluation of hypertension in hospitalized children is provided in Figure 26-1.

HISTORY

In obtaining a history, the clinician should focus on disorders or conditions that predispose to hypertension and, in a hospitalized patient, should begin with the history of present illness leading to the child’s admission. For instance, in a postoperative patient who is otherwise healthy, pain or anxiety may play a role in hypertension. In a child hospitalized with severe reactive airway disease, steroid therapy or frequent administration of β-agonists may be problematic.

In the absence of an obvious precipitating factor related to an acute illness or medical condition, the history should begin with the perinatal period. Prematurity is a risk factor for hypertension, because premature babies are born with fewer nephrons, have a reduced renal reserve, and may be more prone to hyperfiltration injury and glomerulosclerosis as both a child and adult. In addition, placement of umbilical catheters in the nursery or periods of hypotension early in life can mediate renal injury by thrombosis or hypoperfusion with increased risk for subsequent renal scarring.

Especially in preschool children, febrile urinary tract infections commonly leave renal parenchymal scars that can then lead to hyperreninemic hypertension over time. These infections may have been misdiagnosed or even gone unappreciated, so any history of unexplained recurrent febrile illness should be elicited.

Glomerulonephritis presents with edema, hematuria, and hypertension and may be isolated to the kidney or associated with systemic inflammatory disorders such as systemic lupus erythematosus. Relevant extra-renal findings include joint symptoms, rashes, and recurrent unexplained fevers or constitutional symptoms. Recent systemic infections may also lead to postinfectious glomerulonephritis and may be associated with gross hematuria or tea-colored urine in addition to high blood pressure.

The family history focuses on relatives with pediatric or early-onset hypertension and inherited diseases that affect the kidneys, such as the polycystic kidney disease complexes, tuberous sclerosis, and neurofibromatosis. A strong family history of cardiovascular disease, such as coronary artery disease, stroke, and hyperlipidemia, suggests similar risk to a hypertensive child as adulthood is reached.

Certain medications are known to cause hypertension, including oral contraceptives, corticosteroids, stimulants, decongestants, and the calcineurin inhibitors (cyclosporine, tacrolimus) that are the mainstay of immunosuppression in transplant patients. Recreational drugs with stimulant effects, such as cocaine, nicotine, and ephedra, can also raise blood pressure, as can withdrawal from the effects of central nervous system depressants such as ethanol or narcotic analgesics.

The review of systems should evaluate for symptoms such as headache, chest pain, visual changes, or mental status changes, because these may be related to severe hypertension or end-organ damage. Sweating, palpitations, and flushing are associated with states of catecholamine excess such as occurs with a pheochromocytoma.