Little patients, big numbers: Evaluating and managing infant hypertension

Early recognition of hypertension in infants can prevent severe morbidity and mortality. But, as with older children and adults, the diagnosis in infants is sometimes hampered by inaccurate blood pressure (BP) readings. And, once the presence of hypertension is confirmed, the list of differential diagnoses is long. This review provides a framework for diagnosing hypertension in infants, especially newborns, and for evaluating and treating its common causes.

Obtaining an accurate BP reading The most accurate way to measure BP in an infant is directly, through an indwelling umbilical or peripheral arterial catheter. But such catheters are generally used only in the sickest newborns in an intensive care setting. Most commonly, BP is measured indirectly, with the oscillometric technique. These devices measure mean arterial pressure (MAP) based on oscillations of the arterial wall during cuff deflation. Manufacturer-specific algorithms then "back-calculate" the systolic and diastolic pressures. BP readings obtained by this method are 1 to 5 mm Hg lower than direct measurement,¹ a disadvantage outweighed by their ease of use and ability to measure BP repeatedly over time.

Accurate measurement of BP requires the use of an appropriately sized cuff. A cuff that is too small can result in a falsely elevated reading. A variety of cuff sizes should, therefore, be available in the nursery or office. The length of the cuff bladder should be 80% to 100% of limb circumference. The recently published Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents recommends a cuff bladder length-to-width ratio of 2:1 to avoid measurement errors associated with improper cuff dimensions.²

One author has recommended a standardized protocol for evaluating BP: 1.5 hours after the last feeding or intervention, apply the appropriately-sized cuff, wait 15 minutes to make sure the infant is at rest, and then obtain three successive readings at two-minute intervals.³ This regimen may be cumbersome in a busy nursery or office but should probably be followed in the initial evaluation of infants with suspected hypertension to prevent an error in diagnosis. When time constraints preclude waiting to take a BP, a reasonable alternative is to obtain BP while allowing the infant to suck on a pacifier treated with a concentrated sucrose solution. Use of a sucrose-coated pacifier to augment analgesia is common before painful procedures in nurseries, such as circumcision. Numerous studies have shown that administration of sucrose reduces crying and heart rate during noxious stimuli.⁴

Defining hypertension in the smallest patients At birth, BP correlates well with gestational age and birth weight. In both preterm and term newborns, BP normally increases with gestational age, postconceptual age, and birth weight. The clinician must take these factors into account to determine whether an infant's BP is elevated.