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Chapter: Medical Physiology: Fetal and Neonatal Physiology

Special Problemsof Prematurity

All the problems in neonatal life just noted are severely exacerbated in prematurity.

Special Problems of Prematurity

All the problems in neonatal life just noted are severely exacerbated in prematurity. They can be categorized under the following two headings: (1) immaturity of certain organ systems and (2) instability of the different homeostatic control systems. Because of these effects, a premature baby seldom lives if it is born more than 3 months before term.

Immature Development of the Premature Infant

Almost all the organ systems of the body are immature in the premature infant, but some require particular attention if the life of the premature baby is to be saved.

Respiration. The respiratory system is especially likely tobe underdeveloped in the premature infant. The vital capacity and the functional residual capacity of the lungs are especially small in relation to the size of the infant. Also, surfactant secretion is depressed or absent. As a consequence,respiratory distress syndrome is a common cause of death. Also, the low functional resid-ual capacity in the premature infant is often associated with periodic breathing of the Cheyne-Stokes type.

Gastrointestinal Function. Another major problem of thepremature infant is to ingest and absorb adequate food. If the infant is more than 2 months premature, the digestive and absorptive systems are almost always inadequate. The absorption of fat is so poor that the pre-mature infant must have a low-fat diet. Furthermore, the premature infant has unusual difficulty in absorbing calcium and, therefore, can develop severe rickets before the difficulty is recognized. For this reason, special attention must be paid to adequate calcium and vitamin D intake.

Function of Other Organs. Immaturity of other organsystems that frequently causes serious difficulties in the premature infant includes (1) immaturity of the liver, which results in poor intermediary metabolism and often a bleeding tendency as a result of poor formation of coagulation factors; (2) immaturity of the kidneys, which are particularly deficient in their ability to rid the body of acids, thereby predisposing to acidosis as well as to serious fluid balance abnormalities; (3) immaturity of the blood-forming mechanism of the bone marrow, which allows rapid development of anemia; and (4) depressed formation of gamma globulin by the lym-phoid system, which often leads to serious infection.

Instability of the Homeostatic Control Systems in the Premature Infant

Immaturity of the different organ systems in the pre-mature infant creates a high degree of instability in the homeostatic mechanisms of the body. For instance, the acid-base balance can vary tremendously, particularly when the rate of food intake varies from time to time. Likewise, the blood protein concentration is usually low because of immature liver development, often leading to hypoproteinemic edema. And inability of the infant to regulate its calcium ion concentration frequently brings on hypocalcemic tetany. Also, the blood glucose concentration can vary between the extremely wide limits of 20 to more than 100 mg/dl, depending princi-pally on the regularity of feeding. It is no wonder, then, with these extreme variations in the internal environ-ment of the premature infant, that mortality is high.

Instability of Body Temperature. One of the particular prob-lems of the premature infant is inability to maintain normal body temperature. Its temperature tends to approach that of its surroundings. At normal room temperature, the infant’s temperature may stabilize in the low 90°s or even in the 80°s F. Statistical studies show that a body temperature maintained below 96°F (35.5°C) is associated with a particularly high incidence of death, which explains the almost mandatory use of the incubator in treatment of prematurity.

Danger of Blindness Caused by Excess Oxygen Therapy in the Premature Infant

Because premature infants frequently develop respira-tory distress, oxygen therapy has often been used in treating prematurity. However, it has been discovered that use of excess oxygen in treating premature infants, especially in early prematurity, can lead to blindness. The reason is that too much oxygen stops the growth of new blood vessels in the retina. Then when oxygen therapy is stopped, the blood vessels try to make up for lost time and burst forth with a great mass of vessels growing all through the vitreous humor, blocking light from the pupil to the retina. And still later, the vessels are replaced with a mass of fibrous tissue where the eye’s clear vitreous humor should be.

This condition, known as retrolental fibroplasia, causes permanent blindness. For this reason, it is par-ticularly important to avoid treatment of premature infants with high concentrations of respiratory oxygen. Physiologic studies indicate that the premature infant is usually safe with up to 40 per cent oxygen in the air breathed, but some child physiologists believe that com-plete safety can be achieved only at normal oxygen con-centration in the air that is breathed.

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