Respiratory distress syndrome (RDS) or glassy-lung disease or hyaline membrane disease (HMD)

Respiratory distress syndrome (RDS) of the newborn, also called glassy-lung disease or hyaline membrane disease (HMD), is responsible for approximately 20,000 newborn infant deaths per year. 

Before birth, the respiratory passage are filled with fluid. At birth, this fluid-filled passageway must become an air-filled passageway, and the collapsed alveoli must expand and function is gas exchange. 

The success of this transition depends largely on surfactant, which lowers surface tension in the fluid layer and eases the expansion of the lungs.

Surfactant is present in the fetal lungs as early as 23 weeks, and by 28 to 32 weeks the amount present is sufficient to prevent alveolar collapse during breathing. Surfactant is produced continuously by type II alveolar (septal) cells and can be detected by amniocentesis.

In the newborn whose lungs are deficient in surfactant, the surface tension of the alveolar fluid is 7 to 14 times higher than normal.

Consequently, during expiration after the first inspiration, the alveoli collapse almost to their original uninflated state.

Immense muscular effort is needed to expand the lungs for each breath.

RDS is more common in premature babies delivered by caesarean section than by the normal vaginal route. 

It is suggested that the stress of being born vaginally produces higher cortisol levels. 

Cortisol, in turn, stimulates surfactant production by type II alveolar cells.

Pregnant mothers at risk of delivering a baby prematurely may be given cortisol to enhance development of the fetal type II alveolar cells.

A treatment called positive end expiratory pressure (PEEP) is used to treat RDS of the newborn.

It consists of passing a tube through the air passages to the top of the lungs to provide needed oxygen-rich air at continuous pressures of up to 14mm Hg. Continuous pressure keeps the baby's alveoli open and available for gas exchange.

The addition of human surfactant to the oxygen-rich air counters the effects of RDS of the newborn more effectively and lessens lung damage.