Many experts believe that human milk is the preferred diet for all infants. Breast milk benefits premature infants in many ways. Milk secreted the first 4 to 6 weeks after premature delivery differs in composition from milk secreted after term. Though the fat contents are similar in both, the fat in preterm milk is of a smaller globule size, enhancing its absorption. Absorption of fat from human milk is 95% compared with 85% in preterm formula. Many of the long-chain fatty acids necessary for brain growth also are higher in human preterm milk (Harnosh, 1994). Before 32 weeks’ gestation, active transport of immunoglobulin G across the placenta does not begin in earnest and the immune system is immature. Thus, infants born before this time are immunologically disadvantaged (Goldman et al., 1994). The immunoglobulins present in human milk, however, offer protection to these vulnerable preterm babies. Studies have demonstrated fewer infections in breast-fed preterm infants (El-Mohandes et al., 1997; Goldman et al., 1994; Hylander, Strobino, & Dhanireddy, 1998). Moreover, all breastfed infants appear to have higher developmental and IQ scores (Tudehope & Steer, 1996; Horwood & Fergusson, 1998; Lucas, 1993) than do formula-fed babies.

Preterm infants whose mothers do not plan to breast-feed require a formula designed to provide increased calories, protein, and minerals. These infants generally are switched to a term formula at 36 weeks’ corrected age. Wheeler and Hall (1996) concluded that infants who weighed less than 1800 g at birth and were kept on a preterm formula for 8 weeks after discharge were longer and had larger head circumferences 12 weeks after discharge than did preterm infants who received term formula. The short-term advantages are clear, but long-term benefits are less certain. Extremely premature (less than 28 weeks) babies often experience delays in reestablishing adequate growth after birth. Therefore, recommendations are to discharge these infants home for several months on an intermediate formula, such as Neocare, which has 22 kcal/oz. The long-term benefits of this approach have not been documented clearly.

Occasionally, an infant with high metabolic expenditures (eg, chronic lung disease, malabsorption, neurologic impairment, congenital heart disease) requires a higher kcal/oz formula after discharge as well. These babies are at slightly higher risk for hyperosmolar dehydration and may need monitoring of their electrolyte levels if they experience vomiting or diarrhea (Trachtenbarg & Golemon, 1998).

Incidence of BPD and CLD is inversely proportional to birth weight and gestational age. It is directly proportional to the presence and severity of respiratory distress syndrome (RDS), the absence of antenatal corticosteroid exposure, aggressive mechanical ventilation, high oxygen requirements, pneumothoraces, fluid overload, hemodynamically apparent patent ductus arteriosus (PDA), sepsis, Caucasian race, male sex, and low Apgar score. In addition, heredity seems to play a role, because incidence is associated with a strong family history of asthma and an HLA-A2 haplotype (Farrell & Fiascone, 1997; Abman & Groothius, 1994; Nickerson & Taussig, 1980).

Several advances in neonatal care responsible for the decreasing incidence of CLD may be responsible for the continued high incidence of BPD. These advances include the following:

The cause of BPD is multifactorial. Both ventilator-associated barotrauma and exposure to high oxygen concentrations are essential to survival in the treatment of RDS, to which premature babies are frequently exposed. Ventilator-associated barotrauma and exposure to high oxygen concentrations, however, are capable of initiating an inflammatory reaction in the lungs (Farrell & Fiascone, 1997). Each of these factors causes an influx of neutrophils into the lungs, damaging them by generating oxygen-free radicals that release inflammatory mediators. These mediators, in turn, attract more neutrophils, creating an ongoing cycle of damage (Frank, 1992; Groneck et al., 1994). Premature babies have underdeveloped pulmonary antioxidant systems, making them particularly susceptible to oxygen toxicity.

Infection and colonization of the airway with Ureaplasma urealyticum has been identified as a risk factor for BPD. Pneumonia of any viral or bacterial etiology also may contribute to the development and severity of BPD, because pneumonia leads to activation of the inflammatory cascade, prolonging the need for mechanical ventilation.

Different neonatal units use different modalities, including the following:

Primary care providers deal with a spectrum of patients with BPD after they graduate from the NICU. Their conditions range from apparently asymptomatic with normal growth, to mild CLD requiring diuretics and enhanced nutritional needs, to more severe CLD requiring supplemental oxygen and various medications.

Assuming the provider participated in the baby’s care prior to discharge, the initial outpatient visit should occur no longer than 2 weeks and ideally a few days after discharge. Follow-up visits may be necessary every few days to every few weeks until the infant has adjusted fully to home care and is doing well clinically. The provider periodically should attempt to reduce or eliminate therapies when the patient is asymptomatic and growing well.

As these patients grow, new lung tissue forms over a period of about 8 years, and pulmonary function improves. They may have abnormal pulmonary function for the rest of their lives, even if only noted in formal pulmonary function tests (Northway et al., 1990; Galdes-Sebaldt et al., 1989). They have experienced the double-edged sword of mechanical ventilation and supplemental oxygen during a critical period of lung development, ultimately leaving them with decreased numbers of larger-than-normal alveoli, gas exchange surface area, and pulmonary reserves.

Babies with BPD seem to require small amounts of oxygen for prolonged periods. Providers must avoid marginal oxygenation or hypoxia. The increased pulmonary vascular resistance that accompanies BPD improves with high-normal pO₂ levels and is worsened by low-normal levels or hypoxia. General recommendations are to maintain oxygen saturations above 92% (Rush & Hazinski, 1992; Koops, Abman, Accurso, 1984). Low-flow oxygen therapy by nasal cannula is preferred, because high flow use is associated with drying of the nasal mucosa. Adequate growth is a marker of adequate oxygenation (Moyer-Mileur et al., 1996).

The weaning process should begin when the baby has experienced no respiratory symptoms for weeks and has shown an increase in growth of 20 to 40 g/d. Providers should record oxygen saturations in all states. If a baby does well in some states but not others, support must increase during those times of stress. Feeding and deep sleep are examples of times when oxygen requirements increase; perhaps they should serve as the last frontier in the weaning process. Good growth is a very good indicator of the child’s tolerance to the weaning process.

Airway hyper-reactivity frequently occurs in these patients, manifesting itself as increased work of breathing, inspiratory crackles, expiratory wheezing, and increased inability to handle concurrent viral illnesses. Bronchodilators are used widely for these problems and seem effective in decreasing the work of breathing, energy expenditure, and consequently caloric requirements. Of inhaled beta-mimetics, albuterol is most commonly used in NICUs.
Dosage starts at 1 mg in 2 to 3 mL of normal saline regardless of weight (0.2 mL of the 0.5% solution) and is adjusted either up or down, depending on its effects or the appearance of adverse reactions (eg, sustained tachycardia). Anticholinergic preparations like ipratropium bromide, especially in concert with beta-mimetics, also have been used successfully.

One difficulty concerns the method of administration (eg, nebulizer, metered-dose inhaler) and the variable delivery to the distal airways. In addition, controversy exists over chronic versus as-needed use, based on asthma literature suggesting that chronic therapy ultimately increases mortality and worsens control (Barrington & Finer Neil, 1998). Methylxanthines (aminophylline and caffeine) also can be used as bronchodilators but are more commonly used in the acute management of apnea. Few babies are discharged home on methylxanthines for CLD. These medications have a narrow safety margin (more true for aminophylline than caffeine). Many outside factors affect serum levels, side effects are common, and frequent levels are necessary. Their role as a major treatment modality even in asthma has fallen dramatically.