An apparatus built on the "open" system for determination of pulmonary gas exchange in the newborn infant after birth is described. At four-minute intervals diluted expired air (5-7 1/min) was collected in bags. The oxygen and carbon dioxide fraction in the bags were analysed with a Nyons Diaferometer (working on the principle of thermoconductivity). In calibration experiments using a gas-mixing technique a high degree of linearity was found, both in the determination of the fraction of oxygen and carbon dioxide (r equal to 0.9996). Reproducibility from duplicate readings was also good (for oxygen determination 0.9% and for carbon dioxide determination 0.8%). Duplicate determinations performed on infants with the same degree of motor activity resulted in an estimated error of the method of 5.8% for VO2 and 7.8% for VCO2 respectively. A metabolic chamber was used to control environmental temperature. The air temperature and wall temperature in the chamber were regulated by water from a thermostatically controlled waterbath and were kept equal within 0.5 degrees C. As the method for determination of the fraction of oxygen and carbon dioxide is not specific, other gaseous materials exhaled by the infants influence the measurements and nitrous oxide was found to interfere with the determinations, and made VO2 and VCO2 determinations in these patients impossible. Experience from more than 50 investigations on newborn infants has shown that the method is well suited to this particular type of study.

Carbon Dioxide↗

PubMed1975

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.

Acid-Base Equilibrium↗

PubMed1973