The influence of different environmental temperatures on pulmonary gas exchange and blood gas changes after birth.

The oxygen uptake (VO2) and respiratory exchange ratio (R) was determined during the first 20 min and at one and at 2 hours after birth in 16 healthy full-term newborn infants studied in different environmental temperatures. Arterial blood gases and acid-base balance were determined on repeated blood samples from the abdominal aorta. The infants were grouped in a "warm" group (n equal to 10) where efforts were made to avoid cooling after birth, and a "cold" group (n equal to 6) where a decrease in rectal temperature to a mean value of 35.4 degrees C at 2 hours occurred. Irrespective of environmental temperature, VO2 was approximately 10 ml/kg min during the first 8 min after birth, thereafter decreasing to about 6-7 ml/kg min. During the first 8 min the main increase in PaO2 occurred and about 2 ml/kg min of the VO2 was accounted for by changes in oxygen stores after birth. At 16-20 min and at 60 min after birth a negative relationship was found between VO2 and PaO2. During the period 8-120 min after birth a close relationship was found between VO2 and the degree of muscular activity. Within 4-16 min after birth, R values above 1.0 were regularly found simultaneously with the main decrease in PaO2. In infants kept "cold" a tendency to hyperventilate was found, probably elicited by cold stimuli. The rapid drop in deep body temperature regularly seen after birth could thus not be explained by a limited ability to increase pulmonary gas exchange. A high degree of evaporative heat loss, a relatively low "basal" metabolic rate and a limited response in "non-shivering thermogenesis" seem to be the main reasons for the heat loss after birth.