23 RESPIRATORY WATER LOSS IN RELATION TO ACTIVITY IN FULLTERM NEWBORN INFANTS

Abstract

In the newborn infant water loss from the skin has earlier been said to contribute 75% to the total insensible water loss. With a method for direct measurement of respiratory water loss (RWL) we have found that this loss contributes more than 50 % to the total insensible water loss at rest in fullterm infants on their first day after birth. The influence of activity on the respiratory water loss has now been studied in ten healthy fullterm infants on their first day after birth.RWL is measured with 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. During the measurements the infant is placed in an incubator with carefully controlled air temperature, humidity and air flow velocity. The infants are then studied at different activities, from deep sleep to furious crying.RWL was 4.2 mg/kg min with the infant at rest in an ambient humidity of 50 % and an ambient temperature of 32.5 °C. Oxygen consumption was 5.4 ml/kg min. Both RWL and oxygen consumption increased with increasing motor activity. When the infant was crying RWL increased to 10.8 mg/kg min while oxygen consumption increased to 8.2 ml/kg min.