Summary

The goals of the initial evaluation of a child or adolescent with elevated blood pressure in the family doctor's office include:

1. Confirmation of the presence of hypertension by repeated measurements.
2. Asking for detailed history and performing physical examination to identify secondary causes.
3. Identifying any co-existing co-morbid risk factors.
4. Identifying any end organ damage.
5. Stratifying the treatment plan according to the current recommendations, and
6. If appropriate, initiating referral to other colleagues or specialists with more experiences in managing children with hypertension.

摘要

家庭醫生在初步評估兒童或青少年高血壓時旨在：

1. 經多次量度血壓，確診高血壓；
2. 從問診和身體檢查，鑒別高血壓病因；
3. 鑒別是否有其他的致病危險因素；
4. 鑒別是否有終器受損；
5. 按現行建議，在不同層次制定治療計劃；
6. 適當地轉介予較有治療兒童高血壓經驗的專科醫生。

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Introduction

Hypertension has been a major cause of morbidity and mortality in adults and it is becoming more and more commonly seen in children.¹ It has become obvious that hypertension can begin in childhood and contribute to the early onset of cardiovascular disease in the adult. The long-term health risks to these children may be substantial. Family doctors need to become adept at evaluating children with hypertension and make treatment a priority. Until validated norms become available in Hong Kong, normative data for childhood blood pressure in the literature can provide a valuable source of reference.

Definition of hypertension in children

Since the initial report from the Task Force on Blood Pressure Control in Children (commissioned by the National Heart, Lung, and Blood Institute), the definition of normal blood pressure during childhood has been re-examined recently.^2,3 With new information gained from the 1999-2000 National Health and Nutrition Examination Survey (NHANES), the childhood blood pressure data were updated in the recent "Fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents". The new tables now include the 50^th, 90^th, 95^th and 99^th blood pressure percentiles by sex, age and height. Hypertension in children and adolescents continues to be defined as systolic and/or diastolic blood pressure, persistently over the 95^th percentile. In-line with the Seventh Report of the Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7),⁴ a new category, pre-hypertension, has also been applied to those with blood pressure in between the 90^th to 95^th percentiles. For stage 1 hypertension, it is now defined as blood pressure in between the 95^th to 99^th percentiles plus 5 mmHg. Stage 2 hypertension is defined as blood pressure above the 99^th percentile plus 5 mmHg. However, these recommendations are not outcome based, as long-term sequelae of hypertension such as stroke and myocardial infarction rarely manifest during childhood. Therefore, the significance of pressure above the 95^th percentile in children and adolescents has never been determined. Furthermore, whether these data are suitable to be extrapolated to the children in Hong Kong is unclear. Sung et al. have recently published the local blood pressure data, measured by oscillometric method, in over 14,000 Hong Kong Chinese school children.⁵ The data were presented in age specific, height specific and weight specific percentiles (from 5^th to 95^th percentiles). Due to the lack of information on the 99^th percentile and absence of data among children younger than 6 years old, it is quite difficult to reconcile the data with the current recommendations proposed by the Fourth Report. Until more comprehensive local data become available, it seems reasonable and up to the choice of the individual practitioner in Hong Kong, to use either the data from Sung et al. with modifications, or to use the published data in the Fourth Report, albeit not specific for children in Hong Kong.

Epidemiology of hypertension

In the United States, the prevalence of hypertension in children has been estimated to be between 2 to 5%.^6,7 Attributable to the increase in childhood obesity, the prevalence of hypertension in children is rising.^8,9 According to the cross-sectional assessment of blood pressure in nearly 7000 adolescents in the Houston, Texas school district, during the period of 2003 to 2005, around 20% of the studied children were at risk for hypertension.¹⁰

As obesity among children is now a global health concern, the Student Health Service of the Department of Health in Hong Kong studied the prevalence of obesity among local primary and secondary school students.¹¹ Using the definition of obesity as measured weight above the median weight for height x 120%, the prevalence has increased gradually from 12.1% in 1997/1998 to 14.1% in 2000/2001. Although large scale population based epidemiological study on childhood hypertension is currently not available in Hong Kong, the body mass index (BMI) has been shown to correlate with blood pressure in both obese and non-obese Chinese children, and it is thus a reasonable assumption that the prevalence of hypertension among children and adolescents in Hong Kong is also rising.¹² Moreover, the recent follow up data from the Hong Kong Cardiovascular Risk Factor Prevalence Study (CRISPS) showed the age-adjusted overall prevalence of hypertension in 2000 to 2004, compared to 1995 to 1996, increased from 18.1% to 23.2% and from 16.9% to 17.2%, in adult men and women, respectively.¹³

Aetiologies

The aetiologies of hypertension in children can be divided into primary and secondary causes. Table 1 depicts the most common causes of hypertension in childhood. Secondary hypertension is more common in children and renal disease is the most common cause.^14,15 Among 1025 Polish children with hypertension, renal parenchymal diseases were identified in 68% of patients while renovascular and endocrine disorders were diagnosed in 10% and 11% of children respectively.¹⁶ In spite that only a few traditional herbal medicines are known to increase blood pressure, every practitioner needs to include herbal medicine as a potential cause of hypertension in children. Documented Chinese herbal medicines that can elevate blood pressure include Ma Huang (麻黃; Ephedra sinensis), Gan Cao (甘草; Licorice), and Ren Shen (人參; Ginseng). Transient rise in blood pressure due to caffeine use and psychological stress is also common. Although essential hypertension is less likely to be encountered in young children, recent studies suggested that primary hypertension might become more prevalent in children referred to specialized centres.¹⁷ Significant risk factors for primary hypertension in children include positive family history and obesity. It is often linked to other risk factors that entail metabolic syndrome, including low plasma high-density lipoprotein, elevated plasma triglycerides, abdominal obesity and insulin resistance.

Table 1: Common causes of hypertension in children at different developmental stages

Newborn/Infancy   Renal arterial or venous thrombosis Renal arterial stenosis Multicystic dysplastic kidney disease Coarctation of aorta Asphyxia Bronchopulmonary dysplasia Toddler   Renal arterial stenosis Reflux nephropathy Coarctation of aorta Medication (e.g. cold remedies) Childhood   Glomerulonephritis Renal arterial stenosis Coarctation of aorta Hyperthyroidiam Hyperaldosteronism Wilm's tumor Medications (e.g. cold remedies, caffeine) Essential hyprtension Adolescents   Essential hypertension Reflux nephropathy Glomerulonephritis Hyperthyroidism Hyperaldosteronism Medications (e.g. illicit drugs, cold remedies, caffeine)

According to the National High Blood Pressure Education Program (NHBPEP) recommendations, children three years of age or older should have their blood pressure measured when seen by medical personnel.³ Hitherto, there is no screening programme in Hong Kong; the most likely circumstance that children discovered to have hypertension are during sick visits to general practitioners or family doctors. General practitioners and family doctors, thus, play a pivotal role in the care of children with hypertension and they should familiarize themselves with the updated consensus and guidelines. Despite the fact that it can be challenging to obtain a reliable blood pressure measurement in a 3-year-old child, with enough practice, it is not insurmountable. Unfortunately, the current medical system in Hong Kong requires most patients to pay out of their pockets for every visit, and patients may not always receive care consistently from a single medical provider. These obstacles render the follow-up of these children difficult, if not impossible.

The roles of the family doctor

1. Confirm the presence of hypertension by repeated measurements

Proper technique is critical to correct measurements of blood pressure. The child should be allowed to sit quietly for 5 minutes. Their feet should be on the floor with the back supported. The arm is supported with the antecubital fossa at the level of the heart. The lower limb should not be used for measurement, except when you suspect a diagnosis of coarctation of aorta and when you need to perform measurements in all 4 limbs. Always use a cuff that is appropriate to the size of the child's limb. The width of the bladder should be 40% of arm circumference at the point midway between the olecranon and the acromion. The length of the bladder should cover 80 to 100% of the arm circumference. An oversized cuff can underestimate the blood pressure, whereas an undersized cuff can overestimate the measurement.

The preferred method for blood pressure measurement is the auscultatory method. The first Korotkoff sound (appearance of clear tapping sound) defines the systolic pressure; whereas the fifth Korotkoff sound (disappearance of all sounds) defines the diastolic pressure. The measured blood pressure should then be compared to the age, sex and height percentile specific data. It is entirely within the discretion of the practitioner to choose the source of the reference data. If the blood pressure is greater than the 95^th percentile, the blood pressure should be repeated twice during the same office visit to test the validity of the reading. Although it is difficult to ask patients to come back to have their blood pressure measurement repeated for financial and social reasons, according to the NHBPEP guidelines, it does require the documentations of blood pressure over the 95^th percentile be made for 2 more visits before one should be labelled as hypertensive.

1a). Pitfalls in blood pressure measurements

Although mercury sphygmomanometer is still being used in some private doctors' offices in Hong Kong, it is expected to fade out with more stringent environmental control. Available options include the aneroid sphygmomanometer and oscillometer, but how accurate are these alternatives? A recent report from Mayo clinic indicated that with vigilant maintenance, when compared to mercury, most of the readings by aneroid apparatus under-estimated the blood pressure by 0.5 mmHg, and virtually 100% of the values from the aneroid device were within the 4-mm Hg range.¹⁸ Park et al. studied the accuracy of oscillometric device in measuring blood pressures in over 7,000 children in Texas.¹⁹ In the study, the blood pressure measurements by an oscillometer (Dinamap 8100; Critikon, Tampa, FL, USA) were compared to those measurements by mercury sphygmomanometer. For all children combined, the systolic readings by Dinamap were 10 mmHg higher than the auscultatory readings. The Dinamap diastolic readings were also 5 mmHg higher. Hence, although the oscillometers are designed for easy operations, and to avoid inter-operators variations, cautions must be exercised in diagnosing hypertension. Children with elevated blood pressure measured by oscillometric devices should have measurements repeated using auscultation. At times, paediatric trainee doctors may find it difficult even to measure blood pressure in children by auscultations but I trust, with adequate practices, family doctors and the colleagues in general practice can prevail in measuring blood pressure in young children.

Ambulatory blood pressure monitoring requires the patient to wear a portable monitor that records blood pressure over a specified period. This allows the doctor to diagnose patients with white-coat hypertension. Unfortunately, this is not readily available to most family doctors and general practitioners in Hong Kong. The other alternative is to encourage home monitoring. Automatic blood pressure monitors that use the oscillometric method are currently available in almost every local dispensary or the department stores in Hong Kong. Most of them are reasonably reliable (I personally recommend the use of the upper arm type), easy to use, and quite inexpensive. Many families in Hong Kong may already be using them regularly to check blood pressure of their elderly at home. Although it is still debatable how reliable is the home blood pressure measurements in predicting cardiovascular outcomes, it is a logical, viable and much cheaper option, other than performing the 24 hour ambulatory blood pressure monitoring. One of the drawbacks is the need to find a cuff that is suitable for children.

2. Differentiate between primary/secondary hypertension and identify existence of co-morbid risk factors

Once hypertension has been confirmed, a comprehensive history and careful physical examination should be conducted to identify any underlying cause for the elevated blood pressure. Figure 1 depicts an algorithm adapted from the NHBPEP to help family doctors in Hong Kong to manage children with hypertension.³ 

Figure 1 Approach to management of childhood hypertension in Hong Kong

 

2a). History and physical examination

Table 2 depicts the items that should be included in the history. Children with primary hypertension often have a positive family history of hypertension or cardiovascular disease. Other co-morbid conditions or risk factors such as snoring may also associate with primary hypertension (Table 3). A careful history will uncover these important elements. Medication history, especially use of over-the-counter medicines, Chinese herbal medicines, illicit and prescription drugs should be enquired.

Table 2: Relevant histories in children with hypertension

History A) Past medical history Prematurity Bronchopulmonary dysplasia History of umbilical artery catheterization Head or abdominal trauma Pyelonephritis or frequent urinary tract infections B) Family history Hypertension Heritable diseases (e.g., neurofibromatosis) C) Dietary history Caffeine Licorice Salt consumption D) Others Snoring Smoking Drinking alcohol Medications (e.g., cold remedies) Illicit substances abuse

Table 3: Common co-morbid conditions associated with primary hypertension during childhood

Obesity Family history of hypertension Family history of cardiovascular diseases Familial hypercholesterolemia Diabetes

Although the physical examination finding of a hypertensive child is usually normal, physical signs such as goiter and fine tremor (hyperthyroidism), absent femoral pulses (coarctation of aorta) and cafe au lait spots (neurofibromatosis), when present, will be very helpful in pinpointing to a specific diagnosis. Moreover, due to the strong association of hypertension with increased BMI, the BMI should be calculated. Blood pressure readings in the other upper and lower extremities should also be obtained in suspected case of coarctation of the aorta. Retinal examination should also be included.

2b). Laboratory tests

Screening tests should be performed on all children with a confirmed diagnosis of hypertension. The Fourth Report suggested that a complete blood count, renal panel and urinalysis should be performed as part of the initial evaluation. Decisions about additional testing should be guided by the history, presence of risk factors, physical findings and the results of the screening tests. Young children and those with stage 2 hypertension usually require more extensive work-up to detect secondary causes of hypertension. The family doctor may elect to refer the patient to a specialist for further management. On the other hand, children with obesity and a family history of diabetes require further evaluations for the metabolic abnormalities such as dyslipidemia.

3. Identify any end organ damage

Hypertensive children and adolescents should also be screened for existing end organ damage at diagnosis and regularly during follow-up visits. Due to the lack of studies to correlate childhood hypertension to cardiovascular risks, the long-term health consequences of hypertension detected during childhood and adolescence, as compare to adult onset, are yet to be elucidated. Nevertheless, it has been shown that coronary artery plaques correlate with systolic blood pressure in young adults dying from other causes.²⁰ Studies from different countries have also demonstrated that elevated blood pressure readings during childhood are predictive of adult hypertension (BP tracking) and left ventricular hypertrophy has been suggested to be used as a clinical marker.^21-25 Cardiac abnormalities detected by echocardiography are found in a substantial proportion of adolescents with hypertension, even at initial diagnosis.^26,27 The prevalence of left ventricular hypertrophy, in a recent retrospective study from Houston, was reported to be 15% and 30% in adolescents with stage 1 and stage 2 hypertension, respectively.²⁸ Documenting left ventricular hypertrophy is an important component of the initial evaluation. If echocardiography is not readily accessible, the patient should be referred to facility where it is available. Although it is open to dispute, due to the earlier onset of hypertension and the extended lifetime exposure, it is logical to argue that children with hypertension have a particularly high risk for cardiovascular complications.

4. Stratify the treatment plan according to the current recommendations

The management of childhood hypertension should be individualized. Life style modifications and pharmacologic treatments should be tailored to the individual's age, the stage of hypertension, and response to treatment. Despite life style modifications are notoriously difficult to achieve in the outpatient settings, if family doctors can collaborate with the schools and Department of Health by providing health educations to the public, it may help to vanquish these obstacles. Table 4 depicts some recommendations from the author that may help to overcome some of the obstacles in management of children with hypertension in Hong Kong.

Table 4: Barriers perceived by respondents towards evidence-based practice

All respondents N=857 (%)   Mean barrier score for Subgroups #       Least to quite important   Neutral   Very to most important   HKD N=276   CFP N=422   TCP N=159 Q1 Time Constraint   151 (20)   282 (38)   309 (42)   3.2   3.3   3.4 Q2 Difficulty in accessing evidence at the point of care   170 (23)   271 (37)   297 (40)   3.2   3.2   3.2 Q3 Poverty of local evidence   143 (19)   275 (37)   323 (44)   3.2   3.4   3.3 Q4 Lack of knowledge and skills   324 (44)   270 (36)   145 (20)   2.6*   2.6^   3.0*^ Q5 Limited relevance of research to daily practice   276 (37)   285 (39)   175 (24)   2.7   2.8   2.8                             # Mean barrier score by Likert scale : 5=most important, 1=least important HKD=Respondents from all registered doctors in Hong Kong CFP=Respondents from Hong Kong College of Family Physicians TCP=Training Course Participants * ^ Differences in perceived barriers significant at p<0.05 (student's t-test)

4a). Life style modification

Life style modifications should be part of the blood pressure control regimen. Regular exercises, weight control, low fat and low salt diet, stress control, stop smoking and drinking alcohol should be attempted. Although ingesting salt rarely induces hypertension in normotensive subjects, salt sensitive hypertension is much more common in hypertensive patients. A "no salt added diet" with plenty of fresh fruits, vegetables and low fat dairy and protein similar to the DASH (Dietary Approaches to Stop Hypertension) diet may be successful in lowering blood pressure in children.²⁹ Although it is difficult for the busy primary care practitioners in Hong Kong to monitor the adherence of hypertensive children, life style modifications are currently recommended as the initial treatment for children with prehypertension or stage 1 hypertension. Children who are symptomatic, in presence of end organ damage, with stage 2 hypertension or fail to response to life style modifications should step up to pharmacological therapy.

4b). Pharmacotherapy

On top of life style modifications, children with secondary hypertension or stage 1 hypertension with end organ damage should be managed with pharmacologic agents.³ Goal of treatment is to reduce the blood pressure to lower than the 95^th percentile in the absence of end organ damage or any coexisting risk factors. When end organ damage or coexisting illness is present, the goal should be to lower to less than the 90^th percentile. The antihypertensive agent should be initiated at a low dose and then titrated up. A second drug should only be introduced if the blood pressure fails to respond after reaching the maximum dose. Unless in the presence of specific indications or contraindications, the choice of initial drug is mostly made at the discretion of the doctor and keeping the regimen simple is vital to improving adherence. More and more drugs are now available for children, but detailed review on individual medication is beyond the scope of this discussion. The readers are referred to the Fourth Report for further details.³ Nonetheless, no medication is without side effects and Table 5 depicts the indications and side effects of some commonly used anti-hypertensives among children. A recent survey among trainees of the Hong Kong College of Family Physicians suggested that the most commonly prescribed first line antihypertensive agent, though not specific for adults or children, was diuretic, followed by beta blockers.³⁰ Both diuretics and beta blockers have long-term safety and efficacious profiles in paediatric patients. However, the author's personal preferences are either angiotensin converting enzyme (ACE) inhibitors or calcium channel blockers, though it is by no means to indicate that these medications are better or safer than others.

Table 5: Common classes of antihypertensive that have been used to treat childhood hypertension

Class   Indications/Advantages   Contraindications/side effects   Example and dose recommendations               ACE inhibitors   Diabetes Reduce micro-albuminuria and proteinuria LVH regression Most of them can be given as single daily dose   Fetopathic Cause hyperkalemia Cause acute renal insufficency especially during dehydration Cough   Lisinopril 0.07 mg/kg/day by mouth; single daily dose gradually increase to 0.6 mg/kg/day not to exceed 40 mg/day               Angiotensin Receptor Blockers   Same as ACE inhibitors   Same as ACE inhibitors   Losartan 0.7 mg/kg/day by mouth; single or 2 divided doses not to exceed 50 mg/day may gradually increase to 1.4 mg/kg/day not to exceed 100 mg/day               Calcium Channel Blockers   Migraines Can be used in asthmatics Long acting calcium channel Amlodipine can be crushed for easy administration   May cause facial flushing tachycardia and oedema blockers can be given daily and does not have "rebound" when miss single dose   Amlodipine 0.06 mg/kg/day; single daily dose not to exceed 10 mg/day               Beta Blockers   Migraines Steroid induced hypertension   Avoid use in asthmatics, diabetic patients and patients with heart failure Cause decrease in athletic performances   Propranolol 1 mg/kg/day; in 2 or 3 divided doses may gradually increase to 4 mg/kg/day Titrate the dose to avoid bradycardia               Diuretics   Indicated in volume over-loaded patients   Dehydration Hypokalemia Metabolic alkalosis Hyperlipidemia   Hydrochlorthiazide 1 mg/kg/day; 2 divided doses may gradually increase to 3 mg/kg/day not to exceed 50 mg/day

5. Referral to specialist

Table 6 listed the common problems encountered by private medical practitioners in Hong Kong when treating children with hypertension. Nonetheless, it is not mandatory that all children with hypertension should be referred to a specialist. If the family doctor is familiar with the actions and side effects of antihypertensive, and feels comfortable of following up children with hypertension, the practitioner can choose to manage the patient at his/her clinic. On the other hand, it is still prudent to refer children with stage 2 hypertension, especially in presence of co-morbid risk factors and end organ damage, to other colleagues or specialists with more experience in dealing with this condition.

Table 6: Common obstacles encountered by private practitioners in Hong Kong in managing children with hypertension

* Do not have a permanent primary care physician * Routine health maintenance check up has not been part of the culture in Hong Kong * Most patients pay consultation fee out of pocket, thus reduces the incentives for regular follow-up * Any simple laboratory investigation may impose financial burden to the family * The busy schedule at the clinic precludes in depth health education to patients and their families * Life style modification is notoriously difficult among the children

Conclusion

Hypertension is becoming a common enough paediatric problem. The evaluation guidelines of hypertension in children have been updated recently and the norms for adults should not be extrapolated to children. Health-care providers to patients of all ages need to be aware of this and tailor their screening strategies, so that therapies can be instituted early. In most instances, a detailed and thorough history and physical examination, supplemented with simple laboratory investigations, are all that need to differentiate between children with primary and secondary hypertension.

Key messages

1. The prevalence of hypertension in children and adolescents is rising.
2. Tracking of blood pressure suggests that elevated blood pressure during childhood predicts hypertension in adulthood.
3. The preferred method of blood pressure measurement is auscultation and abnormal measurements obtained by oscillometric devices should be repeated by auscultation if feasible.
4. Correct measurement requires a cuff that is appropriate to the size of the child's upper arm.
5. Elevated blood pressure must be confirmed on repeated visits before labelling a child as having hypertension.
6. Home blood pressure monitoring is a reasonable alternative if frequent follow up is not feasible or if "white coat hypertension" is being suspected.
7. Management of hypertension in children should be individualized.

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Reference