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