Good normative data on blood pressure in healthy newborns are surprisingly hard to find. A recent study (2003–2005) of 406 healthy Australian newborns using an oscillometric method, averaging three readings for each baby, confirmed previous work showing that there is a relationship with postnatal age, particularly between day 1 and 2 of life, but failed to demonstrate a significant relationship with weight ( ). The values are shown in Table A4.1 and Figure A4.1 .
|BP IN mmHg||DAY 1 (RANGE)||DAY 2 (RANGE)||DAY 3 (RANGE)||DAY 4 (RANGE)|
|Systolic||65 (46–94)||68 (46–91)||69.5 (51–93)||70 (60–88)|
|Mean||48 (31–63)||51 (37–68)||44.5 (26–61)||54 (41–65)|
|Diastolic||45 (24–57)||43 (27–58)||52 (36–70)||46 (34–57)|
While an indwelling arterial catheter is undoubtedly the ‘gold standard’ method for measurement of blood pressure, the data produced from studies using this method inevitably reflect the sick nature of the population. Over 12 552 blood pressure measurements were made with oscillometry in 373 stable infants (292 preterm) born in Belgrade over a period of 27 months ( ). These data confirmed other studies, again showing a relationship with postnatal age, gestational age, and weight ( Fig. A4.2 ). The mean blood pressure at each gestation was slightly lower than the gestational age in weeks between 24 and 32 weeks ( , Table 6), but this remains a useful aide-memoire in an emergency, particularly as others have found the 10th centile for the mean BP to be a little higher than this ( Fig. A4.3 ) ( ). In other words, the mean BP of a 28-weeks’ gestation baby is generally above 28 mmHg in the first few days of life. It is important to appreciate that this is not the case after a week or two (see below). The data of are also valuable for preterms, but do not give a value for the mean BP ( Fig. A4.4 ).
Several studies, including that of , have shown that the blood pressure of preterm babies rises quite rapidly over the first few days (and first 2 weeks) of life, with the systolic blood pressure increasing by about 2.5 mmHg/day for the first 5 days and then at about 0.25 mmHg/day. This has led to devise a helpful table of values of normal blood pressure after the first 2 weeks of life ( Table A4.2 ). For older infants, the data of the Second Task Force of the National High Blood Pressure Education Programme, published in 1987, remain the most widely available reference data, but were based on a single Doppler measurement in awake infants, and a revision is awaited. In the meanwhile, helpful data for monitoring infants with chronic lung disease (who can develop hypertension) are provided by ( Fig. A4.5 ).