ABSTRACT
It has long been known that humans lose water and weight insensibly. As early as 1614, Sanctorius (1) observed an insensible reduction in body weight over a period of several hours, during which the subject was placed on a sensitive balance. With the introduction of increasingly sophisticated balances, insensible weight loss (IL) has been one of the principles for determination of insensible water loss (IWL). In 1917 So¨derstro¨m and Du Bois (2), using a calorimeter, found that healthy men lost about 25% of their produced heat through evaporation of water from the skin and respiratory passages. Later, Levine and coworkers found that compared with adults, infants lost slightly more of their produced heat by evaporation under basal conditions (3,4). These authors conducted most of their studies by accurately weighing the lightly clothed infant, but they also measured IWL by means of a ventilated respiration chamber. These studies indicated that the insensible weight and water loss was considerably greater when the infant was outside than when it was inside the respiration chamber. The only plausible explanations for this difference were a slight difference in ambient humidity and a difference in the activity of the infants, who tended to be awake for longer periods when not restricted in the respiration chamber. In later studies with use of a ventilated chamber, Hey and Katz (5) determined both the total IWL and the respiratory water loss (RWL) in infants born at term or near term, and the results indicated greater losses at a low ambient humidity than at a higher one. These authors also calculated the water loss from the skin by subtracting RWL from IWL.
