Studies of respiratory insufficiency in newborn infants. III. Respiratory rates and birth weights of premature infants as guides to their survival and need for oxygen therapy.

A birth weight of 1,750 grams served in the present study to separate premature infants with a good chance of survival from those confronted by grave risks. The fatality rate among infants above this weight was about 2% and for infants below this weight it was about 25%. Severe respiratory disturbances occurred in about 20% of infants with birth weights over 1,750 gm and in about 80% of infants under this weight. Initial apnea and bradypnea occurred among the heavier weight group, but the survival rate among such infants was good. In contrast, among infants in the lower weight group, initial apnea and bradypnea were associated with a high incidence of severe respiratory disturbances and a high fatality rate. Deaths in the first week of life were not observed among 248 premature infants whose respiratory rates did not increase significantly after the first hour, but death did occur in 23 of 102 premature infants who had significant increases in the respiratory rates on the first day or two after birth. Twenty-seven of sixty-one infants with birth weights from 1,001 to 1,750 gm survived without oxygen therapy; 9 of these 27 infants weighed less than 1,501 gm at birth; the smallest had a birth weight of 1,225 gm. The results suggest that oxygen therapy can be withheld with some confidence in the case of infants with birth weights from 1,001 to 1,750 gm, provided the infants (1) are free of cyanosis within a few minutes of birth, (2) initiate sustained, spontaneous respirations within 2 minutes of birth, (3) attain a respiratory rate of 40/min or more during the first hour, and (4) do not have a significant increase in respiratory rates after the first hour. No deaths occurred among 13 infants who fulfilled the above criteria; only one received oxygen therapy and this was begun on the sixth day of life because of pneumonia. The incidence of oxygen therapy, and of deaths, was very high among infants with birth weights from 1,001 to 1,750 gm who did not fulfill the above criteria. Fourteen of nineteen infants with initial apnea, and 10 of 11 infants with initial bradypnea, received oxygen therapy, and about 50% in each group died. None of the six infants who had both initial apnea and bradypnea survived, although all received oxygen therapy. There were 24 infants who did not have initial apnea or bradypnea, but did have a significant increase in the respiratory rates; 16 received oxygen therapy and 3 died. The indications for discontinuing oxygen therapy were difficult to determine for infants with birth weights less than 1,751 gm. These infants, if they belonged to respiratory Group III, often developed sudden, unexpected bradypnea and apnea after apparently recovering from the initial respiratory disturbances of the first 2 days. Late bradypnea and apnea were associated in this study with a fatality rate of about 60% among infants with birth weights under 1,751 gm. The criteria for discontinuing oxygen therapy in small premature infants will continue to be indefinite until some means is found for predicting the occurrence of late, severe bradypnea and apnea with greater accuracy than is at present available.