Blood pressure levels of preterm infants in the first year of life

The development of cardiovascular and cerebral vascular control in preterm infants

Over the past three decades there has been a steady increase in the incidence of preterm birth. The worldwide rate of preterm birth is estimated to be 9.6% of all births, a total of almost 13 million births annually. Preterm birth is associated with a range of adverse cardiovascular and central nervous system outcomes, which may be attributed to altered development of these systems following preterm birth. Preterm birth has a considerable impact on cardiovascular parameters with preterm infants displaying higher heart rates and reduced blood pressure when compared to term born infants at matched ages. Furthermore, premature infants have altered autonomic control of cardiovascular parameters which manifests as abnormalities in heart rate variability and baroreflex mediated control of heart rate and blood pressure. As a result, systemic cardiovascular parameters can be unstable following preterm birth which may place stress on the neonatal brain. The brain of a preterm infant is particularly vulnerable to these fluctuations due to immature cerebral haemodynamics. Preterm infants, particularly those who are very preterm or unwell, display fluctuating pressure-passivity between systemic blood pressure and cerebral blood flow representing a considerably increased risk of cerebral haemorrhage or hypoxia. This is further compounded by immaturity of cerebral blood flow-metabolism coupling, which means increased metabolic demand cannot adequately be met by increased cerebral blood flow. It has been suggested that adverse long-term outcomes following preterm birth may occur as a result of exposure to physiological stress either in-utero or early in infancy.

PEDIATRIC UROLOGICAL CAUSES OF HYPERTENSION

PURPOSE

We reviewed the association of hypertension with several common pediatric urological conditions.

MATERIALS AND METHODS

We comprehensively reviewed the published literature linking hypertension with urinary tract infection, renal scarring, vesicoureteral reflux, multicystic dysplastic kidney, ureteropelvic junction obstruction and posterior urethral valves.

RESULTS

Hypertension is a recognized sequela of several common pediatric urological conditions. It is thought to be a direct consequence of renal damage or scarring often resulting from vesicoureteral reflux and/or febrile urinary tract infection. Multicystic dysplastic kidney has rarely been shown to cause hypertension when examined in large series rather than as isolated case reports. Ureteropelvic junction obstruction and posterior urethral valves have been linked to hypertension, although to our knowledge no series to date has specifically examined this relationship and smaller retrospective reviews seldom describe associated hypertension.

CONCLUSIONS

Several pediatric urological conditions are known to cause hypertension. However, methodological flaws in the literature, including a lack of standardized blood pressure followup, highly variable patient populations and poor control of concomitant urological abnormalities, greatly limit the ability to establish a causative link between any 1 specific condition and hypertension. Early diagnosis, the prevention of infection, close clinical followup and early intervention remain the primary means of preventing pediatric urological causes of hypertension.

Childhood hypertension. An update on etiology, diagnosis, and treatment

In the general population, an estimated 70% or more of premature morbidity can be attributed to tobacco use, undertreatment of hypertension, and obesity. From a public health perspective, health-related behaviors that reduce the risk for cardiovascular disease should be encouraged for all children and their families. Pediatricians are obligated to accurately and frequently monitor patients' blood pressures. When discovered, elevated blood pressure should be appropriately investigated, with the evaluation being tailored to the age of the child and to the severity of the blood pressure elevation. Investigation should focus on not only a search for a cause but also target organ effects. Timely recognition of abnormal blood pressure and appropriate interventions are necessary to affect the future development of cardiovascular and renal morbidity and mortality.

Systolic blood pressure in babies of less than 32 weeks gestation in the first year of life. Northern Neonatal Nursing Initiative

AIM

To define the normal range of systolic blood pressure in a non-selective population based sample of babies of low gestation throughout early infancy.

METHODS

Daily measurements of systolic blood pressure were made in all the babies of less than 32 weeks gestation born in the North of England in 1990 and 1991 during the first 10 days of life. Additional measurements were obtained from 135 of these babies throughout the first year of life. Systolic pressure was measured by sensing arterial flow with a Doppler ultrasound probe. It was assumed that blood pressure had never been pathologically abnormal in the neonatal period if the child was alive and free from severe disability two years later. Data of adequate quality were available from 398 such children. Additional data wer collected, for comparative purposes, from 123 babies of 32, 36, or 40 weeks of gestation.

RESULTS

Systolic pressure correlated with weight and gestation at birth, and rose progressively during the first 10 days of life. The coefficient of variation did not vary with gestational or postnatal age (mean value 17%), the relation with gestation being closer than with birthweight. Systolic pressure rose 20% during the first 10 days from an initial mean of 42 mm Hg in babies of 24 weeks gestation, and by 42% from an initial mean of 48 mm Hg in babies of 31 weeks gestation. These findings were not altered by the exclusion of data from 14 babies who had inotropic support during this time. Simultaneous measurements in three centres using an oscillometric technique revealed that this technique tended to overestimate systolic pressure when this was below average. Systolic pressure finally stabilised at a mean of 92 (95% CI 72-112) mm Hg at a postconceptional age of 44-48 weeks irrespective of gestation at birth.

CONCLUSION

Systolic blood pressure 4-24 hours after birth was less than gestational age (in weeks) in only 3% of non-disabled long term survivors. Systolic pressure rose with increasing gestation and increasing postnatal age, but stabilised some six weeks after term, regardless of gestation at birth.

Side effects of 2 different dexamethasone courses for preterm infants at risk of chronic lung disease: a randomized trial

OBJECTIVE

We hypothesized that a pulsed course of dexamethasone would result in better linear growth than a 42-day reducing course in preterm infants at risk for chronic lung disease of prematurity.

STUDY DESIGN

Forty infants with a birth weight of < or =1,250 g who required mechanical ventilation at 7 days of age were randomly assigned to a repeatable 3-day pulse course of dexamethasone commencing immediately or a 42-day (long) course commencing at 14 days of age if they still required mechanical ventilation and supplemental oxygen. The primary outcome measure was linear growth at 36 weeks' postmenstrual age measured by knemometry.

RESULTS

There was no difference in lower leg length at 36 weeks' postmenstrual age. Infants receiving the pulse course had lower rises in blood pressure, less myocardial hypertrophy, and less adrenal suppression. However, more infants required supplemental oxygen at 28 days' postnatal age (14/18 vs 8/21, P < .05) and 36 weeks' PMA (8/16 vs 5/20, P = .12).

CONCLUSION

In preterm infants at risk for chronic lung disease, a pulsed course of dexamethasone has fewer side effects than a long course but may be less effective at preventing chronic lung disease.

Rate of change of blood pressure in premature and full term infants from birth to 4 months

Systolic and diastolic blood pressures were evaluated in a cohort of 61 non-hypertensive premature [very low birth weight (VLBW), n = 16; low birth weight (LBW), n = 22] and full-term [normal birth weight (NBW), n = 23] newborn infants admitted to a neonatal intensive care unit (NICU) and followed to their 4-month age-adjusted outpatient examination. All were receiving routine postnatal care by 7 days of age. Blood pressure was measured at 7 days of age, at discharge from the NICU, and at the outpatient examination. Simple linear regression of blood pressure on weight was used to fit a straight line to the three measurements for each infant and the average regression line for each birth weight group was then obtained. There was a significant correlation between systolic blood pressure and both weight and length at each of the measurement points and also between the change in systolic blood pressure and change in weight from the discharge to the 4-month examination. Diastolic blood pressure tended to follow this same pattern. Gestational age was correlated significantly with the 7-day blood pressure, but postnatal age at the outpatient examination was not correlated with either systolic or diastolic blood pressure. The average slopes of systolic and diastolic blood pressure on weight (mmHg/kg body weight) were virtually identical for the LBW and NBW groups; in contrast, the average slope of the VLBW group was greater than the other two groups, and the difference was statistically significant for diastolic blood pressure. These results show significant group differences in mean blood pressure prior to 4 months of age between VLBW, LBW, and NBW groups and, for the VLBW infants, a steeper slope of the estimated regression line of blood pressure on weight between birth and 4 months.