A premature infant has a systolic blood pressure (BP) of >95 mm Hg. Normal BP values depend on the infant’s gestational age, postnatal age, and birthweight. There is no set definition of hypertension in newborns. American Academy of Pediatrics (AAP) clinical practice guidelines for children and adolescents state that normal BP is <90th percentile, but no guidelines have been established for infants. Hypertension has been defined as follows:
Blood pressure >2 standard deviations above the mean.
Blood pressure >95th percentile for postmenstrual age.
The Task Force on Blood Pressure Control in Children defines hypertension as a blood pressure reading ≥95th percentile on 3 separate occasions.
Hypertension occurs in 1% to 2% of all neonates in the neonatal intensive care unit (NICU); it is less common in term infants (0.2%), and more common in premature infants (75% of hypertensive infants in NICU). It typically occurs either early on (within the first couple of weeks of life) or later on (infant who is a couple of months old with a chronic condition). Persistent hypertension should be treated because it can cause hypertensive cardiomyopathy, nephropathy, encephalopathy, and retinopathy. For a rapid reference of BP ranges for premature and term infants, see Table 70–1. For estimated BP levels at the 95th and 99th percentiles in infants after 2 weeks of age, see Table 66–1. For other detailed BP values, see Appendix C.
How was the blood pressure measured? BP can be measured either by invasive or noninvasive methods. Invasive methods include an indwelling intra-arterial catheter. Noninvasive methods include palpation, auscultation, Doppler ultrasound, and use of an oscillometric device. The most common methods used in the NICU are the indwelling intra-arterial catheter and the oscillometric device.
Invasive method. BP reading from an indwelling intra-arterial catheter is the most accurate (gold standard) of all methods and is the preferred method. It is most commonly placed in the umbilical artery (aorta) or the radial artery, but can also be in the posterior tibial artery. This system uses a pressure transducer where the pressure waveform of the arterial pulse is transmitted by a column of fluid to an electrical signal. If measurements are taken by means of an umbilical artery catheter (UAC), be certain that the catheter is free of bubbles or clots and the transducer is calibrated; otherwise, erroneous results will occur. It provides continuous readings.
Blood pressure measurement by palpation. This is not used because it only measures the systolic BP.
Blood pressure measurement by auscultation. The systolic pressure determination is the appearance of Korotkoff sounds, and the diastolic pressure is the disappearance or muffling of the Korotkoff sounds. This is not recommended because the arterial sounds are either unobtainable or are not reliable in newborns.
Doppler ultrasound method is time consuming and labor intensive and underestimates the systolic BP.
Automated oscillometric devices (electronic pressure sensor) are the most common noninvasive method used in the NICU. This device uses a BP cuff ...