EPIDEMIOLOGY:
It has been estimated that the prevalence of PH in pediatric populations
in North America ranges from 20 to 64 cases per million with the
majority of patients in WSPH class 1, some of whose PH improve with
growth of the lung.1 Epidemiological studies of
pediatric PH are derived from registry cohorts, and as a result, these
data are affected by such factors as study design and the scope of
clinical practice underlying patient selection for these registries.
Geographic coverage, referral patterns, inclusion criteria and disease
definitions may differ between registries, leading to potential
selection bias. Overall, the estimated incidence of sustained PH in all
categories was reported at 4–10 cases per million children per year
with a prevalence of 20–40 cases per million. Importantly, more recent
estimates have shown a striking proportion of infants in Group 3 or
lung-related diseases,5 which often fall under the
care of pediatric pulmonologists.
The prevalence of PH as a diagnosis on admission has significantly
increased in the 21st century as has the cost of
hospitalization.15 Mortality is difficult to assess
but in a recent ICU-based study, at least 144 pediatric PH patients were
dying annually as recently as 2015 and this study excluded patients
dying in neonatal ICU settings or prior to admission to the
ICU.16 We project that 200- 500 pediatric patients
with PH die per year in the USA and PH likely contributes to the cause
of death in most. The understanding of the importance of PH in critical
illness of the most severely ill patients in the ICU setting remains
suboptimal, but issues in the management of severe right ventricular
failure, the role of atrial septostomy or Potts shunt and possible lung
transplantation for advanced disease is discussed below in this
series.17-19CLINICAL
SPECTRUM :
It has been recognized for decades that the primary diseases,
presentation and natural history of PH in children is quite different
from adults, and is uniquely associated with the developmental biology
of the lung and its circulation.3 In the era prior to
the availability of targeted PH pharmacotherapy, the life expectancy of
children newly diagnosed with PH was shorter than
adults.20-22 Infants can often present with critical
illness, unexplained hypoxemia, poor growth and unexplained respiratory
distress. Older infants and children may have failure to thrive,
recurrent seizures or exercise-induced syncopal episodes. As with
adults, diagnosis can be unfortunately is delayed until the disease has
advanced to a level of severity that includes right heart failure. The
pediatric right ventricle appears to handle mechanical loads, summarized
by pulmonary vascular resistance (PVR), before frank cor pulmonale is
present. Similarly, exercise tolerance measured by six minute walk test
is often maintained at a far later stage of the disease than in
adults.22 The histopathology of PAH in children may
differ from that in adults. Pathology tends to show a predominance of
pulmonary arteriolar medial hypertrophy, less fibrosis and fewer
intraluminal plexiform lesions in children, however, children can still
develop aggressive structure remodeling as well.22