THE INFLUENCE OF DIFFERENT ENVIRONMENTAL TEMPERATURES ON PULMONARY GAS EXCHANGE and BLOOD GAS CHANGES AFTER BIRTH

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Abstract
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.