By Dr. Namrata Todurkar
The lungs of a preterm baby are exposed to different challenges after birth. They have to tolerate and adapt to life outside the womb within a matter of minutes. The lung tissue which was supposed to be like sponge, becomes stiff and hard due to deficiency of a vital substance called surfactant. Majority of these infants recover after the administration of exogenous surfactant and continue to get some breathing support. However, a fraction of preterm infants continue to require higher form of breathing support in spite of surfactant therapy, and they commonly suffer with severe Bronchopulmonary Dysplasia (BPD). BPD is the main, if not the only factor determining the length of hospital stay for preterm infants. This blog will briefly describe BPD which is the most common cause for a baby being discharged on respiratory support.
The lungs essentially stay dormant and do not contribute to oxygen and carbon dioxide (CO2) exchange until the time of birth, because the placenta performs gas exchange for the unborn baby. After delivery (in our case, an unexpected preterm delivery), the lungs have to take up the function of gas exchange immediately to ensure optimum oxygen levels in the blood and at the same time exhale CO2 out of the body. A combination of prematurity, excess oxygen use, excess pressure and volume of air delivered via ventilator lead to an almost unavoidable consequence of BPD. Because, BPD is so common, it seems like everything under the sun (in the NICU) is a risk factor. Poor development of lungs (lung hypoplasia), infection, a significant PDA, failure of extubation and fluid imbalances are the most important ones. Factors like poor nutrition, having a low birth weight for a given gestational age, electrolyte imbalances, kidney injury, surgical interventions, prolonged intubation, and many other factors worsen the lung’s condition and result in severe BPD.
As described earlier, BPD is a form of chronic lung disease that develops in newborns treated with oxygen and mechanical ventilation for a primary lung disorder, most often respiratory distress syndrome. It was first described by Northway et al. in 1967. The term bronchopulmonary dysplasia (BPD) rather than Chronic Lung Disease (CLD) is used as the ‘umbrella’ term for all oxygen-dependent babies, as it better distinguishes the neonatal lung process from the CLDs seen in later life. The incidence of BPD in very-low-birthweight (VLBW) babies varies from 15% to 50%. There is an inverse relationship between the incidence of BPD and gestational age. Preventing a preterm birth may help in preventing severe BPD, but agents prolonging pregnancy (in a mom who is already in preterm labor or has ruptured membranes), may not reduce its occurrence.
“Did you know...? Although BPD commonly occurs in prematurely born babies, babies born at term may also develop BPD particularly if they suffer severe initial lung disease, Ex: requiring extracorporeal membrane oxygenation (ECMO)”.
Thankfully, research in Neonatology has helped in better understanding of the changes occurring in lungs and modified practices have led to lower incidence and severity of BPD. However, it would be interesting to know what the ‘Old BPD’ looked like. Infants with old BPD were born before the introduction of antenatal corticosteroids or neonatal surfactant therapy and at a time when ventilators were first being adapted for use in the newborn population. Old BPD was characterized by severe lung tissue swelling, collapse of airways, massive fibrosis and thickening of the lung with areas of cystic changes and overinflation. All this resulted from injury inflicted upon the lungs by above mentioned risk factors and subsequent healing and recurrence of injury followed by repair over and over again.
‘New’ BPD is not primarily the injury-repair paradigm of old BPD, but a maldevelopment sequence resulting from interruption of normal development of lungs. It can be categorized into mild, moderate and severe. The theory behind the development of severe BPD is focused on the effect of increased production of toxic oxygen free radicals. Premature infants have incomplete development of antioxidant enzyme systems and therefore have low levels of antioxidants, thus resulting in inflammation mediated tissue damage.
It may now be easy to understand why steroids are used in the management of BPD. Steroids act by reducing inflammation in the lungs and therefore researchers have studied different types of them. Dexamethasone is a type of steroid given to ventilated babies with an intention to reduce the severity of BPD, help in extubation and shorten the duration on ventilator. Neonatologists always consider a therapeutic trial of corticosteroids in infants with life-threatening respiratory disease who require substantial ventilatory support and supplemental oxygen. The respiratory status of an infant who is responsive to steroids will usually improve over the first 2–3 days of treatment. If they do respond, a 7–10-day course is recommended.
After discharge from the NICU, babies with BPD are at a high risk of recurrent respiratory infections (viral and bacterial). Oral hypersensitivity can occur as a result of repeated negative stimuli to the mouth and lack of development of appropriate feeding behavior. They frequently develop feeding difficulties and are susceptible to gastro-esophageal reflux leading to aspiration. Hence, the strategy employed to manage them is usually to keep the baby free from infection, while gradually weaning them off the ventilator and into progressively lower concentrations of oxygen. Immunization against influenza should be considered, for babies receiving home oxygen therapy. Immunoprophylaxis with Palivizumab against RSV should be given for those getting discharged on supplementary oxygen. They may also require medicines to reduce fluid overload and to reduce pulmonary hypertension. Babies with BPD require a calorie intake approximately 20–40% greater than age-matched infants.
Bottom line: BPD remains the most common form of chronic lung disease in children. Morbidity and comorbidity are high, with chronic illness and long-term neurodevelopmental effects, accompanied by financial costs to families and society. Infants requiring supplementary oxygen at home have the most severe lung disease, as evidenced by their requirement for hospital readmission in the first 2 years after birth being twice that of non-home oxygen-dependent BPD infants. The hospitalization rate, however, declines after the second year, such that hospitalization was infrequent in prematurely born children at 14 years of age, regardless of BPD status. Early gentle ventilatory and nutritional approaches appear critical to overall prevention of BPD.
Dr. Namrata Todurkar, MBBS, MD (Pediatrics), DNB (Pediatrics). Fellowship in Neonatology from National Neonatology Forum India. Fellow in Neonatal-Perinatal Medicine in University of British Columbia. Areas of interest: Neonatal nutrition, Fluid and Electrolyte Management, Inborn Errors, Neurodevelopmental follow-up of preterm infants. Dr. Todurkar is a volunteer blogger at CPBF.