RESPIRATORY WATER LOSS IN FULLTERM INFANTS ON THEIR FIRST DAY AFTER BIRTH

Abstract

The water loss from the skin, has been considered to constitute around 75 % of the insensible water loss (IWL), the remaining 25 % being respiratory water loss (RWL). In previous studies we have found that the water loss from the skin varies with environmental factors such as ambient humidity and air flow velocity, and with factors related to the infant, such as gestational age and postnatal age. In very preterm infants nursed in a dry environment the water losses from the skin were found to be very high on the first days of life. We have developed a method for measurement of RWL to be used in newborn infants. RWL is measured in an open flow-through-system, where air drawn over the face of the infant, picks up the expired gas. The flow of mixed gas is measured with a Fleisch flow-head connected to a differential pressure transducer, and the concentrations of water vapour, oxygen and carbon dioxide in the mixed gas and in the ambient air are measured with a Perkin Elmer mass-spectrometer. RWL, oxygen consumption and carbon dioxide production are calculated from the obtained flows and concentrations. Measurements were made on the first day of life in normal, fullterm infants. During the measurements the infants were placed in incubators with carefully controlled air temperature, humidity and air flow velocity. RWL was around 5 mg/kg min or 25 g/day per infant with the infant at rest in an ambient humidity of 50 % and an ambient temperature of 32.5 °C. Oxygen consumption was around 7 ml/kg min and RQ was around 0.8. Both RWL and oxygen consumption increased with increasing motor activity. When the infant was crying RLW often increased by 100 % as compared to at rest. A linear relationship was found between RLW and ambient humidity with higher values at a low humidity than at a high one.