percentile of BP for gender and height. As with mean BP this can also be
assessed for the entire 24-hour period or for the awake and asleep period
separately. In the absence of definitive pediatric data, the cut off
percentage for BP load signifying hypertension is controversial. Sorof,
et al. [9] correlated BP load in excess of 50% to left ventricular
hypertrophy and this is usually accepted as cut off. Nocturnal dipping is
the physiological fall of BP at night and is defined in children as
greater than or equal to 10% fall in mean systolic and diastolic BP level
from day to night [10-12].
White Coat Hypertension
White coat hypertension is defined as BP levels greater
than 95th percentile when measured in clinic but normal (average BP less
than 95th percentile) outside the clinic setting. It was first identified
in pediatric population in 1991 and is reported to have a pre-valence of
1.2 to 62% [13,14]. A strong correlation has been found between white coat
hypertension and clinic BP levels with the likelihood of white coat
hypertension decreasing as clinic BP increases. It has been suggested that
it is more likely in those children with clinic BP 1-10% above the 95th
percentile and ABPM is likely to have greater yield in this group.
Although initially it was thought to have a benign outcome recent research
suggests the possibility of it being a pre-hypertension state [15].
Masked Hypertension
Masked hypertension is to some extent reverse of white
coat hypertension with normal clinic BP but elevated ABP [16]. Masked
hypertension has also been correlated with elevated LVM and has been shown
to progress to sustained clinic hypertension [6]. Masked hyper-tension is
more frequent among children with a positive family history of
hypertension and those with increased body mass index.
Diurnal Variation/Nocturnal Dipping
Assessment of BP variability by ABPM can also be
clinically useful. Absence of nocturnal dipping has been reported to be
useful in differentiating secondary hypertension from primary hypertension
[10] and has also been significantly correlated with various other renal
conditions [11,12].
ABPM has found utility among children with both renal
and non renal conditions. Among renal disorders it has been correlated
with renal scars in children with chronic pyelonephritis, renal volume and
cysts in polycystic kidney disease, and likelihood of renal artery
stenosis in children with neurofibromatosis [11,17]. Long-term follow-up
of children with haemolytic uremic syndrome has shown abnormalities on
ABPM that were not identified by clinic BP [18].
ABPM has been found to be useful even among certain non
renal disorders. It has been correlated with adverse cardiac events in
young patients with hypertrophic cardiomyopathy and has been found to be
an effective predictor of severity in coarctation of aorta.
Limitations
ABPM does have some major limitations. Unlike adults,
the limits of pediatric ABPM are not based on large population studies or
on hard outcome data. Even the normative data published by Wuhl’s, et
al. [8] are statistical manipulation of previous data and in addition
does not have adequate representation from all racial segments [4,8]. The
algorithms used in ambulatory oscillatory monitors are usually based on
adults and very few studies have been performed for validation of these
monitors in children. Technical limitations have limited its clinical use
to children above 5 year of age.
With increasing experience in its use, ABPM has now
become an important tool in the evaluation and management of paediatric
hypertension. Its use has steadily increased as suggested by a survey of
438 North American pediatric nephrologists wherein 63% were reported to be
using it in their daily practice [19]. Despite its limitations, certain
indications of ABPM are already generally accepted. This includes
identification of white coat hypertension, particularly among those with
clinic BP suggestive of stage 1 hypertension, evaluation for the presence
of masked hypertension, evaluation of drug resistant hypertension and for
monitoring of BP in certain group of children such as those with chronic
kidney disease. Future research should be directed toward obtaining
normative data in healthy non white population, correlating ABPM with well
defined outcomes in youth with sustained hypertension, and evaluating the
efficacy of ABPM in intervention trials in paediatric populations. In
addition though there is evidence of ABPM being cost effective even in
children [20], its utility in resource constrained practices and
developing countries needs to be explored.
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