Neonatal Hypertension Workup

Usually only a limited set of laboratory data are needed in the evaluation of neonatal hypertension. Obtain serum electrolyte, calcium, creatinine, and blood urea nitrogen (BUN) analysis, as well as urinalysis, in looking for renal parenchymal disease. Obtain endocrinologic studies, such as cortisol, aldosterone, or thyroxine, when pertinent history is noted.

Blood pressure measurement

Proper identification of hypertension in the newborn requires accurate blood pressure (BP) measurement. Fortunately, in most acutely ill infants, BP is usually monitored directly via an indwelling arterial catheter, either in the radial or umbilical artery. This method provides the most accurate BP readings and is clearly preferable to other methods.

In infants who do not have indwelling umbilical lines, automated oscillometric devices are an acceptable alternative method of BP measurement. Although BP readings obtained using such devices may differ slightly from intra-arterial readings, they are easy to use and facilitate the monitoring of BP trends over time. BP readings obtained using such devices are also useful for infants who require BP monitoring after discharge from the NICU. Repeat determinations are advised due to the tendency of oscillometric devices to inflate to a preset value on the first reading.

Pay attention to the size of the cuff and also to the extremity used. Most normative BP data, not only in infants but also in older children, have been collected using BP measurements obtained in the right arm. Because BP measurements obtained in the leg may be slightly higher than those obtained in the arm, the use of other extremities for routine BP determination may complicate the evaluation of hypertension. The nursing staff should document the extremity used for BP determinations and try to use the same extremity for all BP measurements, especially in infants who require antihypertensive treatment.^[14]

Measurement of plasma renin activity (PRA) is usually recommended as part of the laboratory assessment in newborns with hypertension, although elevated peripheral renin levels may not signify the presence of underlying pathology, because renin values are typically high in infancy. In addition, plasma renin levels may be falsely elevated by medications that are commonly used in the NICU, such as aminophylline. Keep these factors in mind when interpreting renin values.

Alternatively, suppressed PRA in an infant with hypertension is a significant finding, possibly indicating the presence of a genetic form of hypertension associated with volume overload, such as glucocorticoid-remediable aldosteronism or Liddle Syndrome.

Chest radiography may be helpful in infants with congestive heart failure (CHF) or in those with a murmur upon physical examination.

Perform renal ultrasonography with Doppler of the renal vessels in all hypertensive infants. Accurate renal ultrasonography may help to uncover potentially correctable causes of hypertension (eg, renal venous thrombosis [RVT]), it may detect aortic thrombi and/or renal arterial thrombi, and it may reveal anatomic renal abnormalities or other congenital renal parenchymal disease. Ultrasonography is fast, noninvasive, and relatively inexpensive. The modality has largely replaced intravenous pyelography, which has little, if any, use in the routine assessment of neonatal hypertension.

For infants with extremely severe blood pressure (BP) elevation, angiography may be necessary. Although some investigators have used aortography via the umbilical artery catheter, formal renal arteriography using the traditional femoral vascular approach is much more accurate for diagnosing renal arterial stenosis, primarily because of the high incidence of intrarenal branch vessel abnormalities observed in children with fibromuscular dysplasia. Depending on the expertise available, this may need to be deferred until the infant is larger. Magnetic resonance (MR) and computed tomography (CT) angiography are of little value in infants, as they do not provide sufficient resolution to identify branch vessel stenoses.

Nuclear scanning may demonstrate abnormalities of renal perfusion caused by thromboembolic phenomenon, although obtaining good studies in infants is difficult because of their immature renal function. Obtain other studies, including echocardiography and voiding cystourethrography, as indicated.