338 Respiratory Hazards in the Premature Infant

At birth the newborn infant is required to make an abrupt adjustment to a new environment. Hitherto its existence has been parasitic and its needs have been supplied by the maternal organism. The most immediate dramatic changes required to support extra uterine life are concerned with respiration and the circulation. The infant must achieve a regular respiratory rhythm and be able to expand its lungs fully. At the same time the blood flow through the pulmonary circulation must be adequate for the gaseous exchange to take place between the pulmonary capillaries and the lumen of the air spaces. The necessary adjustment is not achieved without difficulty in some mature infants and is an infinitely more serious problem for the premature infant. Any definition of prematurity has its drawbacks, but the most generally accepted criterion is a birth weight of under 2,500 g. It is to be remembered that twins will be more advanced in their development than their birth weight would suggest and that certain races, such as the negroes, are more mature at a given weight than the white races. Morrison (1952) states that 50 per cent. of all twins are under 2,500 g. at birth. The premature infant is a much more puny specimen than is the offspring of a full-term pregnancy. It has a greater surface area in relation to its body weight and so tends to lose heat and fluid more easily. It has little subcutaneous fat and so its insulation is poor. Furthermore, the cause of prematurity may have some bearing on its chances of survival. Pre-eclamptic toxaemia, ante-partum haemorrhage and rhesus iso-immunization of the mother may result in premature delivery. The first two disorders often result in the infant being severely affected by anoxia and the third causes the infant to be affected with haemolytic disease. Other maternal diseases, such as cardiac disease, tuberculosis and diabetes mellitus, may prevent the pregnancy from going to term and the infant suffers beyond the customary hazards of a premature delivery. In many cases, perhaps as many as 40 per cent., there is no apparent cause for the interruption of pregnancy, and the infant is delivered in a healthy state, but is immature. It now has to assume an independent existence, and good respiratory function is vital. Unsatisfactory respiratory function is responsible for 15 per cent. of deaths among premature infants, according to Keeri-Szanto et al. (1950). Among the very premature infants, 750-1,000 g. birth weight, Potter (1952) found that respiratory failure was responsible for death in 85 per cent. At Queen Charlotte's Hospital we have found that respiratory dysfunction was at least partly responsible for the death of I44 (72 per cent.) of 193 premature infants of all ranges of birth weight from 700-2,500 g. Satisfactory respiratory function depends on the adequacy of the central nervous system, lungs and respiratory muscles and on the absence of pathological changes which are likely to affect respiration.