Andersons pediatric cardiology 1613

renal arterial stenosis,245 renal venous thrombosis, structural renal disorders, raised intracranial pressure from space-occupying lesions, pheochromocytoma, congenital adrenal hyperplasia, and autosomal recessive polycystic kidney disease In one study,246 all infants reviewed with this last diagnosis had established hypertension by 3 months of age Infants requiring extracorporeal membrane oxygenation are also at risk of hypertension.247 Neonates with hypertension are often severely ill, with tachypnea, cyanosis, and congestive cardiac failure Neurologic symptoms are common, with lethargy, apnea, fits, and focal neurologic defects These symptoms may be related to intracranial bleeding or to hypertensive encephalopathy One-quarter of affected infants, however, may be asymptomatic.240 Renal enlargement is uncommon except with renal venous thrombosis Hematuria and proteinuria occur in about half the infants but can be present without hypertension Raised levels of urea or creatinine are common A consumptive coagulopathy with a microangiopathic hemolytic anemia may be present, with thrombocytopenia, fragmented red cells, and prolonged prothrombin and partial thromboplastin times Activity of renin is usually raised in the plasma Control of the hypertension is vital Orally, prazosin (beginning at 10 to 15 µg/kg 2 to 4 times a day and up to 500 µg/kg per day), hydralazine (beginning at 250 to 500 µg/kg 2 to 3 times a day), and propranolol (0.25 to 1 mg/kg 2 to 3 times a day [maximum 2 mg/kg 3 times a day]) are usually successful, though a diuretic may also be required More potent vasodilator agents, such as minoxidil or captopril, an inhibitor of angiotensin-converting enzyme, may be required Acute control of severe hypertension can usually be obtained with an intravenous infusion of labetalol, given at 1 to 3 mg/kg per hour, or nitroprusside at 2.5 to 5 µg/kg per minute The prognosis for hypertensive neonates and infants is largely determined by the underlying cause Most studies describe an overall good outcome for neonates Hypertension is transient in many infants In one small series,241 it was possible to discontinue medication in more than three quarters of hypertensive infants, and at follow-up all but one had normalized their pressures, remaining free from medication Other investigators248 followed up a similar series of hypertensive babies discharged from a neonatal intensive care unit Of the three quarters requiring drug treatment, all had discontinued medication by the age of 24 months Similar favorable outcomes were reported for neonates with aortic thrombosis and neonatal renovascular hypertension249 and for those who developed renal venous thrombosis.250 Of the latter group, two infants who developed hypertension responded to removal of the abnormal kidney Primary, or Essential, Hypertension The primary form accounts for about 90% of hypertension in adults It may be defined as a rise in blood pressure of unknown cause that increases risk for cerebral, cardiac, and renal events In developed countries, the risk of becoming hypertensive during a lifetime, defined for adults as pressures greater than 140/90 mm Hg, exceeds 90%.251 Primary hypertension is commonly associated with other cardiovascular risk factors such as aging, being overweight, insulin resistance, diabetes, and hyperlipidemia There is a strong genetic component in primary hypertension.144,145 Early studies in animals have shown an association with excessive ingestion of salt.252 People with primary hypertension also excrete a salt load more rapidly than normal subjects, and this abnormality is present in normotensive young relatives.253 These observations suggest that a renal abnormality may precede the development of primary hypertension in susceptible people The genetic nature and self-perpetuation of primary hypertension are perhaps the two most recognized characteristics of the condition.254 There are well-described monogenic forms of hypertension, but essential hypertension is likely to involve the complex interplay of many genes.143–145,254 The impact of essential hypertension in adults has led to increasing interest in the early characteristics seen during childhood that are associated with the subsequent development of hypertension There is a large body of literature highlighting the association of events during early life129,133,168 and diet during fetal development, infancy, and childhood that probably influence the eventual levels of blood pressure.136,167,255 Findings relating low weight at birth to an increased risk of death from cardiovascular events in later adult life256,257 have led to further studies exploring this relationship.258–260 Some256 have suggested that the link is a deficiency of nephrons at birth in babies born with low weight Such a deficiency of nephrons may then progress, through hyperfiltration injury in the remaining nephrons, to further glomerulosclerosis and hypertension.261 Babies born at term with low weight have been shown to have significantly higher blood pressures by the age of 6 years than those born with normal weight.262 At birth, however, the initial pressures have been found to be significantly lower, and heart rates significantly higher, in those born weighing less than 2500 g.263 The smaller babies then showed a significantly faster rise in pressure during the first postnatal month, and through the remainder of the first year maintained their pressures at the same levels as the bigger babies, thereby sustaining a higher pressure per kilogram of body weight Premature birth has also been associated with a significantly increased risk of hypertension.264 A role has been suggested for elevated levels of uric acid, contributing to endothelial dysfunction and leading to microvascular and inflammatory injury to the kidney,265 this notion being supported by the finding that levels of uric acid correlated with systolic blood pressures.266 The impact of birth weight and weight gain during early infancy has been studied intensely and shown to be related to the future development of metabolic syndrome.267–269 Investigation and Diagnosis Adults with essential hypertension have been classified according to the activity of renin in the plasma,270 although the significance of this is not established.271 Low levels of renin are common in blacks with hypertension, and there is some evidence that cardiovascular complications, such as cerebrovascular accidents or myocardial infarcts, are rarer if the activity is low The activity of renin, however, is usually normal in children with essential hypertension, although low levels have been reported in children with primary hypertension.79,272,273 In states of high salt intake, however, low-normal renin levels are to be expected The diagnosis of essential hypertension depends on the exclusion of all known causes of secondary hypertension (see Box 60.1) Cardiovascular causes are usually excluded during the clinical history and examination Similarly, the problems produced by the central nervous system, and hypertension related to drugs or metabolic causes, do not pose diagnostic difficulties Renal disease may be apparent from the clinical evaluation, from the examination of urine, or from the measurement of electrolytes in the plasma A hypokalemic alkalosis, which suggests either primary or secondary excess of mineralocorticoids, should be excluded in all cases Activity of renin in the plasma should be carefully determined, and would be expected to be normal in essential hypertension Ultrasonic and nuclear scans of the kidneys are usually appropriate to exclude major structural abnormalities and to identify parenchymal scarring If the clinical history and examination, full blood count, plasma electrolytes, examination of urine, urinary excretion of catecholamine metabolites, thyroid