Neonatal Hypertension

Excerpt

Despite its presence in clinical practice for the past 4 to 5 decades, neonatal hypertension has only recently gained recognition as a distinct neonatal morbidity. The absence of comprehensive normative data on neonatal blood pressure hindered earlier efforts to evaluate and manage this condition. Limitations in the availability of accurate invasive and noninvasive measurement techniques further complicated assessment. Additionally, significant variability in blood pressure based on gestational age, postnatal age, birth weight, and gender within the neonatal population created challenges in defining normal ranges and establishing a standardized definition of neonatal hypertension.

The clinical trajectory, long-term outcomes, and potential sequelae of neonatal hypertension remain incompletely understood. No clear consensus has emerged regarding the appropriate use or selection of antihypertensive medications in affected infants. Current knowledge continues to evolve, with ongoing efforts to clarify the definition, risk factors, etiopathogenesis, and management strategies for hypertension in newborns.

Diagnosis of neonatal hypertension requires systolic or diastolic blood pressure values at or above the 95th percentile for postconceptual age, recorded on three separate occasions. Blood pressure values exceeding the 99th percentile suggest severe hypertension and warrant the initiation of antihypertensive treatment, along with further investigation to determine the underlying cause (see Image. Neonatal Normative Blood Pressure Data).

Blood Pressure Measurements

Blood pressure can be measured via invasive or noninvasive methods.

Invasive methods

The invasive intra-arterial blood pressure measurement and continuous monitoring, regarded as the gold standard, are performed by utilizing an indwelling catheter in the umbilical, radial, or posterior tibial arteries, which is connected to a pressure transducer and, via that, to a multichannel display patient monitor. This method is generally reserved for sick, unstable, or extremely premature infants.

The following steps and precautions should be taken while measuring the blood pressure intra-arterially via the transducer:

1. The transducer must remain positioned at the level of the heart to reflect actual pressure values.

2. Air bubbles in the tubing must be avoided, as their presence can elevate diastolic pressure and lower systolic pressure, distorting the readings.

3. A clear dicrotic notch should appear on the arterial waveform to confirm correct waveform representation.

4. Tubing should consist of low-compliance material and maintain the shortest acceptable length, since longer tubing can falsely reduce measured values.

5. The pressure transducer must be referenced to zero at atmospheric pressure to calibrate correctly.

6. A continuous heparin infusion should be used to irrigate the transducer and maintain line patency, thereby reducing the risk of clot formation.

7. The umbilical catheter must be appropriately sized, as narrow catheters may underestimate systolic pressure.

8. Removal of the umbilical artery catheter is recommended after 5 to 7 days of use. Prolonged catheterization increases the risk of thrombus formation, which may contribute to inaccurate readings and potential complications.

Noninvasive methods

Automated oscillometry is the most common and widely used noninvasive method for measuring blood pressure in the neonatal intensive care unit. This device detects the maximum blood pressure oscillations from arterial blood flow as mean blood pressure, which is then converted into projected systolic and diastolic blood pressures using standard proprietary algorithms. Oscillometric blood pressure measurements generally correlate well with invasive intra-arterial readings. However, automated oscillometry may overestimate intra-arterial systolic blood pressure values by 3 to 8 mm Hg, thereby overdiagnosing hypertension, and becomes inaccurate when mean arterial pressure drops below 30 mm Hg, thus missing hypotension. The device may also underestimate systolic blood pressure in small-for-gestational-age infants. Variations in blood pressure accuracy across studies might stem from the fact that each manufacturer of oscillometric devices employs a unique algorithm to calculate blood pressure, and several studies have highlighted discrepancies among different devices.

For accuracy, the optimum cuff width is suggested to be in a ratio of 0.44 to 0.55, with the arm circumference covering approximately 80% of the patient's arm length. The size should be standardized for uniformity in the results. The blood pressure becomes erroneously high if the cuff size is too small. At the time of measurement, the infant should lie supine, quietly awake, calm, preferably sleeping, and about 1 to 1.5 hours postprandial. At least three readings, 2 minutes apart, should be taken in the right arm as the preferred site. Using a sphygmomanometer is not recommended because the Korotkoff sounds are not loud enough to be reliably audible in this age group of infants. Ultrasound Doppler is rarely used as a regular blood pressure monitoring device, as it can underestimate systolic blood pressure values.