Large Insensible Water Loss (IWL) in Low Birth Weight Infants Treated with a Plastic Heat Shield

Abstract

Published fluid requirements appear to be grossly inadequate for some small premaute infants. To explain the large water needs of these infants, detailed water balance studies were performed during the first six weeks of life on 22 infants whose birth weights ranged between 700 and 1,800 g, mean 1,232 g, and whose weights were appropriate for their gestational age. IWL determinations were made from measurements of loss in body weight over 3-h periods, with the infants nude in standard single walled isolettes, humidity 45 to 90% and the environmental air temperature in the neutral thermal range. In 9 infants with birth weights under 1,200 g, who were below 10 days of age, IWL was 2 to 4 times greater (equivalent to 80 to 120 g/kg/day) than previously reported for larger infants. To elucidate these large lossesm paired measurements were made within 24 h on 11 infants before and after the insertion of a plastic hear shield converting the isolette ito a double walled chamber. Mean IWL within the double waled chamber was 1.5 g/kg/h S.D. 55 compared to a mean of 2.18 g/kg/h S.D. 1.0 under standard conditions (p < 0.001). There is thus a 30% decrease within the double walled chamber. Thses results, in contrast to previous reports, indicate the ability of the small premature infant to markedly increase IWL in a relatively cool environment. These large losses can be reduced by diminishing radiant heat losses. Heat shields are useful not only for controlling the thermal needs of small immature infants but also in significantly reducing fluid requirements.