Andersons pediatric cardiology 1614

function, ultrasonic and nuclear scans, activity of renin in the plasma, and urinary excretion of steroids are all normal, and the hypertension is not severe, then a diagnosis of essential hypertension is usually appropriate Severe hypertension, particularly with a raised activity of renin in the plasma, will necessitate a careful search for a renal or renovascular cause This will involve a renal arteriogram, usually with selective sampling from the renal vein to measure levels of renin in the plasma Management There is no question about the desirability of treating children with severe hypertension Some common considerations need discussing here, however, as they are of general importance in the management of hypertension in all children, and also because some are of unique significance to children The decision to attempt to lower the blood pressure in children must depend, to some extent, on the assessment by the physician of the circumstances of each child The psychosocial effects on an adolescent of forcing a confrontation with the implications of long-term management for hypertension may exacerbate the problem, while also causing undesirable alterations in behavior and growth Compliance, particularly with medication, may be unsatisfactory General dietary and health advice should initially be given The avoidance of risk factors, including a smoke-free environment for the child, should be encouraged Obesity should be treated with caloric reduction, reduction of excess sugary drinks, reduction in intake of saturated fats and salt, and regular exercise A reduced intake of salt, with no salt added to cooking or at the table, is important, with long-term deleterious impact of sodium shown.177,274 A high ratio of polyunsaturated to saturated fats should be encouraged, while foods rich in cholesterol should be avoided, refined carbohydrates reduced, and the content of dietary fiber increased Such advice may seem a counsel of perfection, but much can usually be achieved by a minimum of intervention, and without generating excessive anxiety or food fads For details regarding lifestyle recommendations, recent expert committee guidelines should be consulted.36,37 Compounds known to exacerbate hypertension, such as liquorice, sympathomimetics, and corticosteroids, should be avoided Oral contraceptives must be used with careful monitoring Such measures are probably all that is required initially, together with a relaxed but reliable follow-up to check the blood pressure If the pressure remains obviously unacceptably raised, at more than 99th percentile, or continues to be mildly raised over a period of 1 to 2 years, then antihypertensive treatment may be required Caution regarding treatment of uncomplicated mild hypertension is advisable, and a reasonable interpretation of available evidence would allow advice concerning smoking, dietary changes, hypercholesterolemia, obesity, and exercise The creation of undue anxiety should always be avoided Treatment with drugs to reduce blood pressure seems reasonable, particularly if the lifestyle changes have been unsuccessful, and careful follow-up is assured Hypertension induced by oral contraceptives is common, with an incidence of 7.5% Furthermore, oral contraceptives will exacerbate hypertension in a similar proportion of individuals.275 The mechanism is thought to involve stimulation of the release of renin and aldosterone, a direct effect of estrogen on retention of salt and water, and sensitization of smooth muscle to vasoconstriction produced by angiotensin II Cardiac output may also increase Decisions regarding individual patients will need to take account of individual factors, not least the assessment of the risk of pregnancy It would seem advisable, however, to discontinue oral contraception if hypertension occurs, but not to preclude its use in the presence of preexisting mild hypertension A formulation containing low levels of estrogen should be used A further rise in blood pressure would then be an indication for stopping treatment Up to half of the adults receiving antihypertensive therapy become noncompliant This is probably equally common in children, especially adolescents.276 The quality of the relationship between doctor and patient, the degree of knowledge of the patient and of participation, and the ease of consultation are important factors The ease of administration of the medication, including a reduction in the number of drugs and frequency of ingestion, is important Long-acting formulations requiring once-daily dosage are preferred Alterations in lifestyle, including diet, must be introduced slowly The process of breaking habits is often met with resistance and may also lead to noncompliance in other areas Renal Hypertension Pathophysiology Renin is a proteolytic enzyme that is produced by the juxtaglomerular cells and stored in the afferent arteriole After release into the blood, it reacts with angiotensinogen, a substrate in the plasma produced by the liver, to form the decapeptide, angiotensin I This agent is then further acted on by converting enzyme in the lung to produce the octapeptide, angiotensin II, which raises blood pressure by direct vasoconstriction and by its indirect effects on the nervous system It stimulates secretion of aldosterone, promotes retention of sodium by the kidney, and stimulates thirst and the release of catecholamines and vasopressin.277 Baroreceptors located in the afferent arteriole control the release of renin This is also affected by other factors, including delivery of sodium in the distal tubule to the macula densa, sympathetic activity, catecholamines, and hypokalemia Activity of the renin-angiotensin system is intrinsically related to the balance of sodium and the volume of extracellular fluid The importance of renal ischemia in the generation of hypertension has been appreciated since classic canine experiments.278 The detailed mechanisms, nonetheless, remain controversial.277 Unilateral renal arterial constriction in the rat will produce hypertension If the constriction is removed within a few weeks, hypertension subsides If the clip is left for longer, and then removed, hypertension often persists Removal of the nonclipped kidney, but not the previously clipped kidney, will often result in a fall in blood pressure Concentrations of angiotensin II rise in the plasma with the initial unilateral constriction, and this is probably responsible for the initial rise in blood pressure Thereafter, the concentration slowly decreases, even though the hypertension persists It is likely that the renin-angiotensin system is still responsible for the hypertension at this stage This is partly through its vasoconstrictive action, and partly because of retention of salt.277 Later, after months or years, removal of the abnormal kidney in humans fails to reduce blood pressure It is likely that renin is not involved in the maintenance of the hypertension The mechanism by which the retention of salt causes hypertension is not certain It would be expected that a rise in arterial pressure would lead to a pressure natriuresis If hypertension is maintained without depletion of sodium, then the relation between blood pressure and renal excretion of salt must be reset at a higher level.279 This is perhaps a result of the effect of angiotensin II in reducing renal perfusion and increasing retention of sodium by the kidney, both directly and by the release of aldosterone.277 The persistence of hypertension after the removal of the initial cause in experimental animals has its clinical counterpart in pheochromocytoma, Cushing syndrome, Conn syndrome, and aortic coarctation In these instances, the blood pressure does not always return to normal after removal of the cause The persistent hypertension may be related to damage to the renal vasculature