Physiological characteristics. The follwoing must be considered: physiologic resilience, tempetature, respiratory and circulatory systems, gastrointestinal system, nervous system, sleep and immunity.
(i) Physiologic resilience. Nature provides the foetus and the newborn with a certain physiologic resilience, which means that their systems are not readily affected by abnormal conditions, although there are limits to their tolerating capacity. For instance, the normal neonate is relatively indifferent to a range of body temperature from as low as 36.1°C to as high as 37.7°C; in premature infants, the body temperature may even drop to 34.4°C. The newborn does not seem uncomfortable or show the concomitant signs of low or high temperature that would appear in the adult. The infant is also indifferent to abnormal levels of substances in the blood. Although the blood glucose level may be low, the usual hypoglycemic reaction of the adult is not seen. Furthermore, the infant can survive without breathing for a relatively longer time than the adult.
(ii) Temperature. As mentionned above, the temperature of the newborn varies in an unpredictable way. At birth it is slightly higher than its mother's, since the uterus lies deeply insulated within her body. It drops immediately after birth in adjustment to the temperature of the delivery room and then rises to normal within about eight hours. The newborn's hands and feet are colder than the rest of its body since its circulation is poor.
(iii) Respiratory system. The mechanism of respiration is established before birth but it undergoes changes at birth. The hypoxia resulting from the cutting of the umbilical cord helps in initiating breathing through the stimulation of the respiratory centre. The first breath, usually taken within 30 seconds after birth, helps to expand the collapsed lungs, though full expansion does not occur for several days. Respiration is irregular in depth, rate and rhythm and varies from 35 to 50 per minute. Normally respirations are gentle and quiet, rapid and shallow. If the infant does not cry, it should be stimulated to do so at approximately hourly intervals in order to force expansion of lungs by concomitant, deep respirations.
(iv) Circulatory system. At birth, the circulatory pattern must change from foetal dependency on the placenta to include the expanding lungs. The circulation of the pulmonary system is perfected and shortly after birth, oxygenated blood flows through the infant's body in the same manner as that of the adult.
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